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Spintronics - Science topic

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For a lateral spin valve, why different non-local voltages can be measured when the two ferromagnets are parallel or antiparallel (as shown in the electrochemical potential diagram versus position)?
Figure credit: A. Hirohata, K. Yamada, Y. Nakatani, I.-L. Prejbeanu, B. Dieny, P. Pirro, and B. Hillebrands, “Review on spintronics: Principles and device applications,” Journal of Magnetism and Magnetic Materials, vol. 509, p. 166711, 2020.
Note: I have edited the figure a little for my own use.
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The answer can be derived from electrochemical potential (ECP) calculations and continuity of ECP, charge currents, and spin currents at interfaces.
Reference: S. Takahashi and S. Maekawa, “Spin injection and detection in magnetic nanostructures,” Phys. Rev. B, vol. 67, p. 052409, Feb 2003.
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Hello everyone, I am currently working on a Heusler alloy system which has a non-collinear magnetic order as reported by a earlier study. I intend to further explore this non-collinear magnetic state. It would be really helpful if someone can suggest me some properties that can be investigated theoretically in order to see if it has a potential use in spintronics devices or if it has some kind of other applications. I am using VASP. Thank you.
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you should also go for spin hall conductivity and anomalous hall conductivity calculations using Wannier90 package. other important property is exchange parameters, the strength, range and type of exchange parameters plays an important role in determining Curie temperature and macroscopic magnetism of the materials.
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Dear all
what is the new and HOT promising diluted magnetic semiconductor materials, that can have ferromagnetic and semiconductor properties close to room temperature? Wich not very difficult to realize (based on typical crystal growth techniques, availability of source)
My question is directed for research purposes, not necessarily for commercial applications.
Please share your knowledge. Additionally, If you know a good paper for this question, please tell me.
Thank you in advance.
Best regards.
Ismail
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Ferromagnetic chalcopyrites II-IV-V2 have Tc ~ 310-350 K and a diamond-like crystal structure compatible with Si and III-V semiconductors. Transition metal doping is possible in these materials over the entire range of concentrations from 0 to 100%. Here are two relevant references:
(1) Room temperature ferromagnetism in novel diluted magnetic semiconductor Cd1-xMnxGeP2, Jpn. J. Appl. Phys. 39(10A), L949-51 (2000);
(2) Magnetic and optical phenomena in nonlinear optical crystals ZnGeP2 and CdGeP2, J. Optical Society Am. B 22 (9), 1884-1898 (2005).
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Hi everyone, i'm a beginner with VASP and i have some trouble with my spin polarized relaxation,
in fact i try to relax a 2 x 2 x 2 BiCoO3 tetragonal supercell with different magnetic configuration.
It works well for some but it switchs to orthorhombic latice for others, and i don't know why since the symmetrie shoudn't be broken with Z oriented (by default) spins.
Did someone know how i can force the tetragonal cell while leaving a/c free ?
My INCAR for C-Type AFM :
SYSTEM = BiCoO3
NCORE= 4
PREC = accurate
ENCUT = 550
GGA = PE
LDAU = .TRUE.
LDAUTYPE = 2
LDAUL = -1 2 2 2 2 2 2 2 2 -1
LDAUU = 0 4 4 4 4 4 4 4 4 0
LDAUJ = 0 0 0 0 0 0 0 0 0 0
ISTART = 0
ICHARG = 2
INIWAV = 1
NELMDL = -9
LREAL = AUTO
ISYM = 2
AMIX = 0.4
ISMEAR = -5
LMAXMIX = 4
Ionic minimisation
NSW = 100
ISIF = 4
IBRION = 2
EDIFFG = -3E-2
POTIM = 0.5
ISPIN = 2
MAGMOM = 8*0 -5 -5 5 5 -5 -5 5 5 24*0
Electronic minimisation
ALGO = Fast
EDIFF = 1E-4
NELM = 60
LWAVE = .FALSE.
LCHARG = .TRUE.
Lattice parameter obtained :
7.4820927815601488 7.4261381663482009 9.4695336886550603
Thanks.
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Thank you for your response, i've already started a calculation with a smaller SYMPREC, i hope it will solve my problem.
I was aware of Jahn-Teller distortion but i saw some articles for BiCoO3 by ab initio calculation and everyone converge with a tetragonal solution for this configuration that why i know it's probably wrong.
My POSCAR is an experimental solution with high-spin cobalt.
I will draw my PDOS to look for orbital overlap.
📷
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how to make thin film in simple way of magnetite material??
is there any practical for spintronics applications simulation?/
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The cheapest tools to make thin films without using expensive instruments are hand-held airbrush or hand held drawdown bars. You could get a good quality of films by adjusting your solution concentrations, solvents, and environmental factors such as temperature and humidity.
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This is important today, as it is well-known that a shadow has fallen over the race to detect a new type of quantum particle, the Majorana fermion, that could power quantum computers.
The Nature retraction is a setback for Microsoft’s approach to quantum computing, as researchers continue to search for the exotic quantum states.
While the evidence of elusive Majorana particle dies --- computing hope lives on, and is now made possible by using tri-state+ [1] in software with standard binary hardware, while enabling the use of spintronic methods and other novel approaches using integers [2].
In that, it is useful to desconsider irrationals and infinitesimals, treating them as illusions, and clear the field.
The fact that many irrationals are in physics formulas, although non physical, is another motivation, to simplify. We then obtain new insights, such as a discrete spacetime, and a connection between quantum and GR -- that was already expected.
Mathematics cannot be independent, as all science is interrelated. What is your qualified opinion?
References
[1] Ed Gerck. Tri-State+ Communication Symmetry Using the Algebraic Approach. Computational Nanotechnology. 2021. Vol. 8. No. 3. Pp. 29–35. DOI: 10.33693/2313-223X-2021-8-3-29-35
[2] Ed Gerck. On the Physical Representation of Quantum Systems. Computational Nanotechnology. 2021. Vol. 8. No. 3. Pp. 13–18. DOI: 10.33693/2313-223X-2021-8-3-13-18. Change all occurrences of "Eq.(3)" to "Eq.(4)"
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At the Moscow State University, Setun (Russian: Сетунь) was a three-level logic computer developed in 1958, as well-known. It was arguably the most modern ternary computer, using the symmetric ternary number system and three-valued ternary logic instead of the two-valued binary logic prevalent in other computers.
In 1965, a regular binary computer was used to replace it. But in 1970, a new ternary computer architecture, the Setun-70, was developed; it was implemented as a simulation program running on a binary computer.
This demonstrated that while ternary logic may have computational advantages, binary computers seem to be sufficient and allow GF(3^m) in software --> GF(2^n) in hardware. That is our approach to quantum computing.
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Magnetic Semiconductors, particularly in Spintronics, the spin of the electrons are considered that provides structures that allow for a dramatic reduction in energy consumption. Also, it is known that silicon causes electrons to lose their spin state. Hence, how can this control of the spin for long distances be conceivable?
Kindly share your views.
Thank you!
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The statement that ``silicon causes electrons to lose their spin state'' is (a) incorrect and (b) not relevant, since silicon by itself isn't magnetic. Also, ``long distances'' doesn't mean anything either, without a reference length scale.
It suffices to search for ``magnetic seminconductors spintronis'' to find, for instance this article: https://arxiv.org/abs/1111.1032.pdf
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What material do you suggest to start experimenting on Spintronics and get familiar with this field?
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Dear Abdolazim,
If you are starting to build knowledge in this field, you will probably want to focus at first on spin pumping, direct and inverse spin Hall effects and spin wave propagation. (Other effects will naturally call your attention.) You will need a magnetic material to assemble any spintronic device. For that, YIG is the prototypical magnetic material, because its damping coefficient is lower than any other magnetic material, which ensures higher energy efficiency, smaller precession angle when excited into resonance (which is important if you want to be able to use the linear approximation of the LLG equation for modelling), longer magnon lifetime and longer spin wave propagation. When it comes to spin transmission through interfaces with nonmagnetic metals, the fact that it is an insulator is also an advantage. But it is comparatively much more complicated to fabricate good quality YIG thin films than permalloy (Py), for example, which is also frequently used as spin injector (in spin pumping experiments) and as spin wave propagator.
As for nonmagnetic materials used in spintronic devices, platinum (Pt) is the most used when strong spin-orbit coupling is needed (for spin-to-charge current interconversion) and copper (Cu) is the most used when weak spin-orbit coupling is needed for "spacer" layers.
Although the field of spintronics was propelled by the discovery of GMR, my comments are focused on a more recent trend in spintronics called spin-orbitronics. I hope they can help.
Best regards
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Spin orbit torque (SOT) switching of ferromagnetic layer with perpendicular (Out-of-plane) magnetization requires an additional in-plane magnetic field along the direction of applied charge current.
Could any one please give a lucid explanation for the need of such in-plane magnetic field and also please explain symmetry of which is broken by this applied field?
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Magnetization switching by current-induced spin-orbit torques (SOTs) is of great interest due to its potential applications for ultralow-power memory and logic devices. In order to be of technological interest, SOT effects need to switch ferromagnets with a perpendicular (out-of-plane) magnetization. Currently, however, this typically requires the presence of an in-plane external magnetic field, which is a major obstacle for practical applications. Here we report for the first time on SOT-induced switching of out-of-plane magnetized Ta/Co20Fe60B20/TaOx structures without the need for any external magnetic fields, driven by in-plane currents. This is achieved by introducing a lateral structural asymmetry into our devices during fabrication. The results show that a new field-like SOT is induced by in-plane currents in such asymmetric structures. The direction of the current-induced effective field corresponding to this new field-like SOT is out-of-plane, which facilitates switching of perpendicular magnets. This work thus provides a pathway towards bias-field-free SOT devices.
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I measured the AHE voltage of my hall bar device using a lock-in amplifier; I am a bit confused with the analysis of this data; I have checked in several papers that the y-axis (hall resistance axis ) is usually symmetric about the origin, what is the reason for this;
1.is the centroid of the hysteresis curve is subtracted from all the data, and then it is plotted against the magnetic field?
or
2. since the AHE resistance signal is directly proportional to Mz (z-component of magnetization), so do I have to change the sign of data when I change the voltage values to the resistance values from the point when switching is happening?
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Hi, AHE measurements always come with a geometrical offset due to small nonuniformities in the film or in the patterned geometry, you can state that you arbitrarily remove it or you can actually compensate for it in the measurements by performing two measurements switching current and voltage probes and averaging the two results, see for instance methods in
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Unless there is some systematic error on the instrumentation used, I have observed an inverted peak when measuring the FMR absorption derivative for a YIG/NM/m-FM thin-film sample. The YIG layer was deposited via magnetron sputtering on GGG(111) substrate and is not monocrystalline but exhibits only a few crystalline phases. The observed anomalous peak is normal at lower frequencies, goes through a change at 2.5 GHz and becomes inverted at the higher range. Another peak observed for the same sample (probably corresponding to a different crystalline phase) is not inverted but at least four times more intense, both at lower and at higher frequencies. Both peaks occur on the same FMR dispersion curve.
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I used broadband multi-frequency stripline technique when I obtained inverted peaks. I interpreted them according to homogeneity of the sample and the standing wave due to reflection within the sample and sample thickness.
I hope these information is useful and let us know if there is an other explanation.
Regards
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Valleytronics can be realized by accessing different spins coupled with different valleys. In monolayer TMDs, time-reversal symmetry should be present while spatial symmetry should be broken to realize spin-valley polarization. People use a magnetic field to detect this spin-valley polarization. then why TRS is not broken on applying magnetic field?
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The simple answer to your question is time-reversal symmetry does break, once the system is exposed to an external magnetic field. However, this symmetry breaking can barely affect the valley spin polarization imposed by the breaking of inversion symmetry, and thus, is ignorable. To put this into context, in a heavy metal system such as WSe2, the internal spin-orbit field causing the valley spin polarization can go beyond several hundred Tesla, which is much greater than the external magnetic field which our current technologies can afford.
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In Co/Pt bilayer deposition, why it is that first, we have to deposit an underlayer (usually Tantalum) on Silicon substrate and then Pt, why, in general, Cobalt is not deposited on Silicon while preparing a Co/Pt bilayer?
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The perpendicular magnetic anisotropy (PMA) in the Co/Pt system that appears when the Co thickness is below a critical value (of the order of 1 nm) is due to the interfacial anisotropy at the interface between the Co layer and the Pt bilayer. So, if you start depositing Co instead of Pt, you lose the effect of a possible first interface, and normally what you want is to enhance the PMA…
Even worse: if the Si substrate has native oxide, and you start depositing Co, some Oxygen can form CoO, which may exhibit antiferromagnetic behavior… a complete mess.
Finally, the Ta is used to improve the thermal stability among other beneficial effects. You should have a look at this paper:
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Generally, linear polarized light helps in understanding the carrier dynamics, wheres circularly polarized light will revel the spin relaxation dynamics which is very much necessary for any kind of spintronics applications. I have found that people use achromatic quarter waveplates to do so. It will be really helpfull if anyone provides further necessary details like specification, position of this particular waveplates in TA set up etc.
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Dear Goutam Ghosh,
here some hints for the use of waveplates in pump-probe experiments:
- Selection: Ultrashort laser pulses may have a broad spectrum. As the wave plate should work for all spectral components of the radiation used, achromatic wave plates are feasable and should be optimized for your center wavelength. If you use high intensities (e.g. in the pump beam) you may additionally use a zero-order air-spaced design of the waveplate. All big optics suppliers have tutorial web-pages that allow you to select the right wave plate and you can call them for individual support.
- Position: That depends on your specific pump-probe setup. If adjusted properly in the beam pah, the quarter-wave plate simply converts linearly polarized light to circularly polarized light (or vice versa). For the general adjustment, you can check this tutorial youtube video: https://www.youtube.com/watch?v=EBVNbRN805o
Keep in mind that all optical components that are following the creation of the circularly polarized state may affect (change) this polarization state again. So think twice where to put it and, as a test, carefully check the polarization state at your sample site (measurement position). Also you must consider that your wave plate adds some additioal optical path difference between your pump beam and the probe beams. In other words: the "zero-delay" may change. Moreover, due to the dispersive properties of the wave plate, it may slightly change the pulse duration of your pump or probe beam(s) that could affect your temporal resoution.
Regards, JB
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Recently, the current induced magnetization switching by spin-orbit torque (SOT) using the basic spin Hall effect is identified as a vital ingredient for non-volatile spintronic memory and logic devices.
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Such developments have a great potential for realizing ultra-fast and low-power electronics for the next generation of memory, logic, communication, and quantum technologies
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Spin-based devices such as magnonic chips, spin-torque oscillators mostly find their application in signal processing, computing, etc. Is there any research work focusing on developing magnonic and spintronic devices for medical science?
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Velocity of the electron in the metal is ~ 10^6 m/S which is 1/300 the speed of light. So, If the electron's velocity is not relativistic, then how a moving electron in a material can experience an electric field as magnetic field in its rest frame and hence exhibits Spin-Orbit coupling. How can I understand this.
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What you're talking about is the group velocity of electrons in a metal as a whole when exposed to an external electric filed. Electrons individually perform an orbital motion around the background nuclei which can reach to a relativistic limit especially when the nuclei are heavy with large number of protons. The result of this orbital motion is an internal magnetic field felt by electrons in their rest framework through a Zeeman-like coupling to their spins that is commonly known as the spin-orbit coupling.
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After growing the films of topological insulators, what are the measurements which can confirms the TI?
Most of papers show ARPES is one of the technique which can confirm the growth.
Can one confirm it by transport measurements? or any other measurements?
Thanks in Advance !
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You can first confirm the structural properties, for example using RHEED, LEED and STM. You can also perform XPS measurements and check core levels. Transport measurements would allow you to access the topological surface states if the Fermi level is inside the bulk band gap. If the sample is not bulk insulating, there will be additional contribution from bulk states. ARPES will allow you to check the electronic structure and confirm the existence of topological surface states with a linear energy-momentum dispersion. The connectivity of surface states to the bulk bands should also be visible below the Fermi level. To access the band structure above Fermi level as well as the connectivity of the surface states to the conduction band, one could use time-resolved ARPES . In addition, the dispersion of the bulk bands can be followed using ARPES by varying the photon energy of the incident light. Synchrotron-based ARPES is the best methods of choice. In fact, you should observe an odd number of crossings of the surface states at the Fermi level, which is in correspondence with the odd number of band inversions in the bulk. The helical spin texture of the surface states can be confirmed using spin-resolved ARPES, for example by measuring spin-resolved energy-distribution curves at different k points. The spin texture should reverse above and below the Dirac point. If the Fermi surface is perfectly circular, electron spins should be in-plane and locked to their linear momentum. If the Fermi surface exhibits strong warping, you should aslo be able to detect a non-zero spin polarization in the direction perpendicular to the surface.
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If I do MFM paramagnetic thin film patterned on SiO2, will it give a phase difference like ferromagnetic films?
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Hi,
Basically, I aim to develop a one semester (6 -months) coursework on Magnetic Tunnel Junctions (MTJ).
I am able to find a lot of books on Spintronics with a few chapters on MTJ.
1) Can anybody suggest me a book that specially focuses on every aspect of magnetic tunnel junctions ( Basic introduction and priniciple, working of Magnetic tunnel junctions, theory of spin transfer torque in MTJ, experimental fabrication of MTJ - Materials as well as synthesis perspective, Heusler alloys in MTJ, Theoretical models for characterization of MTJ, Experimental characterization of MTJ).
OR
2) Can anybody suggest a book or two on Spintronics that focuses on MTJs.
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Dear Eesha Andharia.
For what you are looking for I think that you will find this book quite useful:
"Introduction to Magnetic Random-Access Memory", from Bernard Dieny, Ronald Goldfarb and Kyung-Jin Lee.
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How do you measure half metallic nature and the spin polarization of a ferromagnetic material?
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Respected All! May I know the importance of large band gap in half-metallic compound? For example if Co2FeAl gives wider band gap in spin down as compared to Co2MnAl, what can be concluded? or What is the specialty of wider band gap compound over the low band gap one? Can we predict the efficiency of spin-injection or magnetic memory among these two compounds in terms of their spin band gap?
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I think, the materials have wide band gap is important when these materials are strained
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Hello dear researchers, I just started to learn about the valleytronics but its a quite complex to get in this subject. Can anybody give me some useful tricks? also can anybody elaborate in a simple words that what are the differences between the valleytronics and spintronics.
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Kimi Chen Electrons in graphene carry not only electric charge and information about spin, but also information about the so-called pseudospin. Research of the last of these properties will enable the development of a completely new branch of technology - valleytronics (analogous to electronics and spintronics).
Valleytronics and spintronics are essentially similar in that information is coded in a quantum number as opposed to charge for conventionnal electronics. They differ in the quantum number used (i.e. Spin or Valleys).
"Valleytronics" – a new type of electronics in diamond. An alternative and novel concept in electronics is to utilize the wave quantum number of the electron in a crystalline material to encode information. In a new article in Nature Materials,
Isberg et.al. propose using this valley degree of freedom in diamond to enable valleytronic information processing or as a new route to quantum computing.
A potential avenue to quantum computing currently generating quite the buzz in the high-tech industry is “valleytronics,” in which information is coded based on the wavelike motion of electrons moving through certain two-dimensional (2D) semiconductors. Now, a promising new pathway to valleytronic technology has been uncovered by researchers with the Lawrence Berkeley National Laboratory (Berkeley Lab). Like spintronics, valleytronics offer a tremendous advantage in data processing speeds over the electrical charge used in classical electronics. Quantum spin, however, is strongly linked to magnetic fields, which can introduce stability issues. This is not an issue for quantum waves.
References:
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Alloys for example NiFe, CoNi, CoFeB are used in thin films with in-plane and perpendicular anisotropy.
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One reason is to vary the magnetostriction which, in turn, gives better control of the microscopic domain configuration. For example, Ni80Fe20 was used in MR sensors since this composition is close to zero magnetostriction which maximizes the sensitivity and minimizes any inconsistent response due to mechanical stresses.
Fe50Mn50 was often used because this is an antiferromagnetic composition with a relatively low Neel temperature that could also exchange-couple to permalloy.
CoFeB was used as a recording medium because it improved the signal-to-noise ratio because, after annealing, the B would segregate to the grain boundaries of the CoFe. Controlling the size and the magnetic properties of the grains was a back art and a closely guarded industrial secret.
BTW, Fe2O3 is not ferromagnetic. In the hexagonal alpha phase, it is antiferromagnetic, and in the cubic gamma phase it is ferrimagnetic (at least, at room temperature). Most of the ancient recording tapes used gamma Fe2O3.
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Hello everyone, earlier I was using the Gaussian 03 and there I used to include the keyword IOP(5/33=3,3/33=1) to print the Hamiltonian and overlap matrix in output file. But, recently I have switched to Gaussian 09 and using the keywords IOP(5/33=3,3/33=1) in root section, though it prints the overlap matrix but gives null alpha and beta matrix. I also tried 'IOP(5/33=3.3/33=1) pop=full' but for no avail. 
What keyword should I use so that it print the alpha and beta matrix?
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Hello, there use this
iop(3/33=4) pop=full, it will show you the overlap matrix
Regards
Ajay Khanna
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What are the available tools for spintronic device simulation?
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Please check out our website:
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Need free software available for the simulation of spintronic devices like spin transistors and memory devices.
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Please check out our website:
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In recent study of different spintronics system, people are studied that the ferroelectricity in type-II mutiferroics is produced by spin current. I want to know to clear the origin of spin current and how it produced the ferroelectricity in the type-II mutiferroic systems at the magnetic ordering point.
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You should read the following article to get some initial knowledge about spin current.
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At what field are the anomalous Hall conductivity and longitudinal conductivity calculated to determine mechanism (extrinsic or intrinsic or metallic conduction) for magnetism ?
The conductivity can be considered at zero magnetic field where the AHE conductivity is the residual, or at high magnetic field where the AHE conductivity saturates. The first approach makes more sense but there is no clear indication in literature about the field at which the conductivity were calculated. Thank You.
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Very nicely elaborated answer given by Aires....
The AH resistivity (conductivity) always considered in zero field situation that can get by extrapolation of the high field region R-H curve. And off course the averaging remove the effects mentioned by Aires.
Since, the resistivity at high field contain magneto-resistance contribution so do not think to consider the resitivity at any field, therefore, the longitudinal conductivity calculate by the zero field resistivity measurement and use it to evaluate the intrisic and extrinsic contributions. These effect are  explained in the article (http://www.sciencedirect.com/science/article/pii/S0304885317303967?via%3Dihub). Look into this and reference their in.
Hope this help.
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Do you know about some articles calculating the band structures of DMS containing Mn in general and number of holes in Mn 3d band in particular? I need this information to calculate magnetic moment from XMCD measurements. Many thanks in advance.
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see for example:
Structural, electronic and magnetic properties of Fe, Co, Mn-doped GaN and ZnO diluted magnetic semiconductors
Physica B: Condensed Matter, Volume 440, 1 May 2014, Pages 1-9
A. Alsaad
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Dear all,
Confusion is always coming to me when I come across A-type/C-type/G-gype/E-type antiferromagntic arrangement. There is few references on the arrangement of antiferromagntism.   
Can somebody help me to find the earlier reference which classified the antiferromagnetism or help me to  differentiate this??
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If I remember correctly, the first author of a reference given below is the one who introduced A-C-G notation.  His description evolved later, to classify various phases of canted antiferromagnets (~1970-1974).
E. F. Bertaud, R. Pauthenet et M. Mercier, Phys. Lett. 7, 110 (1963)
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Anderson localization insulator can be induced by defect disorder, such as impurity atoms, atom vacancies and so on.
Does anyone know the limited concentration value of defect disorder (such as oxygen vacancies in Pr0.7Ca0.3MnO3) to make Anderson localization, or is there have some papers have studied this question? 
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I don't have a direct answer for you, unfortunately. But my faint memories to lectures on the topic seem to tell me, than Anderson localization was a weak effect, observable at small temperatures in metals. (I may be misled, though) My question would therefor be whether the manganates such as the one you mention are good enough metals such that Anderson localization may take a leading role? 
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How to find the magnetic dead layer film thickness (for magnetic materials such as Co2MnSi, CoFeB,.. alloys) for ultra thin films by experimental method ?
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Thanks Dr. Arnab Roy
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From my EPR spectra, I could see that there is an increase in the derivative of the spectra as a function of doping it with Iron.I have observed from my previous results that there is an obvious formation of iron oxide separately from the main compound nickel oxide. But from this EPR spectra, I am not able to give a direct explanation on the spin-glass, ferromagnetic phase formation. How do I find the direct relation for the uncompensated spin from the spectra?
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The short answer is to measure your EPR spectra as a function of temperature. In the case you have ordered ferromagnetic clusters you don't expect any temperature dependence. In the case of localized random spin distribution, you expect to find a "glass temperature"; I expect your EP resonance to go through a maximum in intensity at the "glass temperature".
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is it possible to have strong spin orbit coupled electronic motion in 3D??
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I agree with the answer of Christian Binek. In fact, the spin-orbit coupling denotes an additional term in the Hamiltonian describing electrons in the periodic potential of the nuclei (see e.g. Ref. [1, Eq. (1.1)]). This term has a relativistic origin and is particularly relevant for materials containing heavy atoms such as bismuth. In topological insulators, the spin-orbit coupling may lead to a spin splitting of the electronic surface (or edge) states. Note that also gold shows a spin splitting of surface states [2], although this is not a topological effect. Furthermore, there are indeed materials which show a spin splitting of the bulk energy bands. The most prominent example in this respect is BiTeI, whose bulk energy bands can be effectively described by the Rashba Hamiltonian. Here, the spin splitting mainly results from the spin-orbit coupling of Bi atoms and the non-centrosymmetric crystal structure of this material (see e.g. [3, 4]).
[1] R. Winkler, Spin-orbit coupling effects in two-dimensional electron and hole systems (Springer, 2003).
[2] S. LaShell, B.A. McDougall, E. Jensen, Phys. Rev. Lett. 77, 3419 (1996).
[3] K. Ishizaka et al., Nat. Mater. 10, 521 (2011).
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PRL 99, 236809 (2007)
In the foregoing article link , I want to know how have they plotted figure 4 (a) in particular?
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I have found the answer, Berry curvature is calculated theoretically using first principle study. But I am not sure yet how one can probe it experimentally.
PRB 86,165108 (2012)
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I just want to know how these two technologies are compatible to each other when we fabricate the STT-MRAM memories. One bit cell of STT MRAM consist of one MTJ + one NMOS transistor. 
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In my case, i have fabricated spin field effect transistors using MOS technology. This is Si/SiO2/magnetic layer and over that contact pads made of Au. The MTJ can also be combined with this subject to suitability of the parameters like material, etc. So, a cell can consist of both MTJ and spin-FETs. I have used oxide layer so that the devices are not shorted. However, if you combine MTJ with that, you need to be sure about the layer thickness of the oxide or of the different layers that you may be depositing for the MTJ device. The MTJ can be fabricated at the same platform on which spin-FET has been prepared or by depositing separate thin layers of laternate insulating/magnetic layers.
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I define the geometry by atlas, uniaxial anisotropy, Magnetostatic energy and exchange interaction by oxs. I define the initial magnetization as
m0 { Oxs_RandomVectorField {
min_norm 1.0
max_norm 1.0
}}
but when I try to visualize the magnetization using Oxs_TimeDriver results 0. Why?
Thanks
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Thanks :D
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I know that when spin is pumped from the FM layer under FMR, the angular momenta is transferred from FM layer to NM layer, which results in increase in damping constant as well as FMR linewidth in bilayer system.
I am curious to know the next steps
1. How the pumped spin results in linewidth broadening? I is it broader for metallic or insulating NM layer?
2. will there be no spin pumping if there is no carriers in the NM layer? on the other hand no linewidth broadnneing?:
3. I am not able to visualize these steps. Can someone please help me?
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Line broadening is a well understood thing in FMR. you do not have to employ complicated names to understand. Line broadening occurs in polycrystalline materials due 1) to inhomgenieities, different magnetic phases or inclusion of non magnetic phase2) conductivity 3) porosity 3) strong anisotropic materiaals. In a single crystal which was my speciality, things are clearer. Just anisotropy and the presence of ions with strong spin-orbit coupling would widen the line width. The simple reason being the precession energy is transferred via spin-orbit coupling to the lattice which absorbs thus dampening the resonance or in otherwords the precession of the spins. These are well explained in any text bookof the 1970s.
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Normally in trilayer structure (Pinned / spacer (nonmagnetic metal) / free layer), status of the free layer was read by the analyser kept in the top of free layer. But in the pentalayer (Pinned layer 1 / spacer (nonmagnetic metal) / free layer / spacer(nonmagnetic metal) / Pinned layer 2), the additional pinned layer is kept above the free layer. Theoretically, we can easily study the magnetization switching by solving the dynamical equation. Experimentally, how can read the magnetization status of the free layer in the pentalayer structure?
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Experimental papers of pentalayer structures are attached herewith for your kind reference. Applied Physics Letters 86, 152509 (2005); doi: 10.1063/1.1899764, Applied Physics Letters 88, 082504 (2006); doi: 10.1063/1.2179124.
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Multilayered Ni / Ag structure was calculated using VASP. I would like to understand how to get from the results of the calculation the specific energy of atomic orbitals. That is, find what orbitals used to construct the total wave function of the quantum numbers and energy.
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the on-site atomic projected DOS can give you this information. 
you can get this for each atom, and also individual orbitals on different atoms by setting LORBIT. LORBIT=10 for instance will let you have projections up to s p d atomic orbitals without the different spatial directions. than all that's left is to plot out the PDOS for the wanted orbital and see where it has a maximum energy
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Researchers are very excited for TIs which show some unique properties such as spin momentum locking and large spin-orbit interaction. they say spins are 100% intrinsically polarized in TI.
I have one confusion. In TI spins transport in two opposite direction with one spin up and other spin down. then how will we get large spin polarization. because we have both spin up and spin down spins.
Please explain it
Thank you
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Time reversal symmetry has it (Kramers Theorem) that single electron (in general: states with an uneven number of fermions) states must be (at least) two-fold degenerate. For a 'normal' electron state this implies spin degeneracy (and hence arbitrary spin dierection as Beibing Huang pointed out. See below, however for a slightly more stringent argument.) 
The normal notion is that the presence of magnetic flux density destroys time reversal symmetry. One can think of time reversal symmetry by considering waht it would mean to let time flow backwards: an object in motion will be at the same place immediately after time reversal but move in opposite direction, so the sign of momentum is reversed. This automatically implies that angular momentum is also subject to time reversal. You shall find this confirmed when considering the trajectory of an electron in a magnetic field.
Quantum mechanically you will know that applying a magnetic field leads to Zeeman splitting and so the 2-fold degeneracy is lifted.
So, in the field free case, the spin degeneracy implies zero magnetization (spin polarization).
In the theoretical description, time reversal symmetry is represented by an antiunitary operator, which involves komplex conjugation. [For an all-time textbook classic on the subject you may want to consider Messiah's text, Volume 2, chapter XV, but similar treatments an be found at other places, e.g. the document linked below.]
Now how about electron/Bloch states in periodic solids? Complex conjugation of a Bloch state describes a state with opposite momentum (just as time reversal did in the classical noteion). So time reversal implies degeneracy of {k,\sigma} with {-k,-\sigma} (where \sigma symbolizes spin). That is still exactly the case in the topological surface state. What is lifted is the degeneracy between {k,\sigma} and {k,-\sigma}. But that, to be precise, was not required by time reversal symmetry! It derives from other symmetries, and breaking those is what may lead to exotic states such as th TI surface states.
About visualizing time reversal symmetry: that is difficult I would say. It is more instructive to consider what can and what cannot induce breaking time reversal symmetry. As said above, presence of magnetic flux density does. Purely electrostatic potentials cannot and therefore never do.
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I need a comprehensive device which can be used to take IV curves, Magnetosreistance, tunneling magnetoresistance and any other relevent technique for MRAM.The device should be cost-effective due to limited budgetary estimates (80,000 USD)
or Measurement of spintronics related characterizations.
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hi. An automatic quasi-static tester (QSW) that measures the resistance vs. magnetic field (VEECO). It is possible to measure the devices using 4 point probe.
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When an electron passes thru a magnet (like in the Stern-Gerlach experiment) the projection of its spin changes. The biggest change is when the projection is perpendicular to the magnetic field. After the  magnet the projection is parallel so it has undergone a 90 degree rotation. (this what I mean by something and hope that anyone would agree).
But now lets look at the energy of the electron. As the energy of the electron does not at all depend on the spin or its projection it follows that its energy hasn't change. It is no wonder as the magnetic field is known not to do work. But then the magnet and its field also doesn't change. That's what I call nothing.
So to summarize:
1. There was a change induced by a system (the magnet) and it hasn't change
2. A system (electron) has undergone a change and it was not connected with energy flow.
How is this possible - it seems to contradict physical laws?
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You say: "the magnetic field is known not to do work", this applies to the (magnetic part of the [generalized, depending on teaching tradition(*)]) Lorentz force, which is the force exerced by (electro-) magnetic fields on charges.
It is not so appropriate to say that there is a rotation of the spin (by 90°, in your example, which, by the way is not the largest possible change).
(a) When a charged object with angular momentum (spin in case of a free electron) is subject to a homogeneous field, then the result is a precession of the spin about the field direction. The scalar product of magnetic moment and magnetic field remains unchanged (and so is therefore the magnetic potential energy. The Larmor precession represents an extra (kinetic) energy, though, if orbital motion was involved).
(b) there is no net force exerced by a homogeneous field onto the spin.
All this, however, is not the situation of the Stern Gerlach experiment and for two reasons: the net charge of the electron leads to cyclotron motion and the beam is therefore bent such as to make the experiment impossible (this is actually, why it was [cleverly] done with neutral silver atoms). Second the deflection is induced by a field gradient. The field gradient is what exerces a force onto the moment and makes a difference between spin up and down.
This deflection, which is necessary to now be able to "measure" the spin component along the field gradient (split beam) of course represents some work being done. In case of an electromagnet kept at constant field (and gradient) this work is effectively done by the power supply.
(*) In some texts the electric component q*\vec{E} is included in what is called "Lorentz force", in others not.
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We have take a trilayer nanopillar consists of two ferromagnetic layer separated by a nonmagnetic metal layer. Suppose if we consider ferromagnetic layers are align parallel(and aligned along easy axis, say X-axis) and ferromagnetic layers lies in XY-plane, then RKKY coupling arises due to the conduction electron reflection at the interface of the ferromagnetic layer. We can be express it interms of the coupling field. My doubt is, In which direction the coupling field will act (in which direction we express the magnetization in the field equation)?
P.S: I herewith attached the article having the expression for RKKY field.
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Ooops.  I was certainly too quick in my last post.  The RKKY interaction is described in terms of wavevector at Fermi level, not of the individual electron.  It is hard to say what will happen to Fermi level when electrons gain some momentum.  It may move both ways, up or down, no possibility excluded a priori.  Nevertheless, in any case, the modulation of RKKY interaction by electric field should be observed.  I think the effect of applied field should produce effects similar to those due to temperature increase.
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I would like to know if you have two layers of ferromagnetic iron nanoparticles inside of conductive polymer matrix layer. Can Scanning Tunneling microscopy spectroscopy be used to observe GMR effect as a significant change in the electrical resistance depending on whether the magnetization of adjacent ferromagnetic layers are in a parallel or an antiparallel alignment. So just with applying magnetic field in STM equipment we can detect these changes? Is this feasible? 
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Over the last two decades a lot of experience has been collected on how to obtain STM tips capable of magnetic imaging. There is not one such recipe but many different ones, depending on the instrumental conditions you have available, and on the problem to be studied. In my paper Atomic-Scale Magnetism Studied by Spin-Polarized Scanning Tunneling Microscopy, published as a chapter in Fundamentals of Picoscience, ed. K. Sattler, CRC Press, I devoted a section on reviewing the various procedures of preparing magnetic STM tips (Note: some libraries provide access to the ebook version). By the way: you will have a hard time finding someone selling you such a tip. There is no market for it. Go ahead, find your own solution.
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How the spintronics is helpful for missile guidance ?
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Hi
Spintronics is a blend of electronics with spin and also based on the spin of electrons rather than its charge.The application based, it's used in the magnetic version of RAM used in computer nonvolatile and another one of MRAM is faster and less power consumption.
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For example, to get answer, could we use classical formula (44.4) from the book Landau,Lifshitz "Theory of field" (see the attached photo) ?
It's because, we suppose, the distance between the electron of conductivity and the atom is equal approximately the distance between two neighbor atoms which can be in interval from R = 10^{-5} cm to R = 10^{-7} cm, whereas the radius of electron orbit is r = 10{-8} cm. Thus (see photo) R >> r. Just in that approximation the formula (44.4) was obtained.
Am I right?
What is magnetic field?
Thank you in advance.
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 Still not sure to get your question, Vladimir.
Formula 44.4 is the field generated by a magnetic dipole moment \vec(m) located at the origin. If the moment can be regarded as fixed in orientation and magnitude, then so os the dipole moment vector and you can straightworwardly go on computing the field at any location in space based on this formula. [You will have to get unit conversions right. 1 Bohr magneton is 9.274E-24 J/T or 9.274E-24 Am2]
There is still an approximation, though: if the source of the magnetic moment is not a "point dipole" but of finite extension, then the formula describes this dipolar field only for sufficiently large distances, well above the characteristic length scale of the magnetic object. In case of an atom or ion, the characteristic length scale will be of the order of a few Angstroms.
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I have to improve the tunnel spin polarization in our devices, however, I do not have MBE equipment. How can I induce a good tunneling barrier?
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it depends in your growth system. 
If you clarify it more we can help
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Hi everybody.
I'm looking for GPU-accelerated packages in DFT calculations, I wonder if anyone knows an accurate package which also supports GPU acceleration (except quantum-espresso), and how much speedup I can gain with gpu in dft calculations?  Also I want to mention that my calculations are in spintronics. 
Best Regards
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Terachem (http://www.petachem.com/products.html) works apparently very well and you can make the calculations much, much faster (x10 or better) - but it's mostly suited to single molecules (like gamess, gaussian and so on), and not really to solid-state problems.
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Does anyone modeled STT-MRAM accurately and published papers..I see some, but if someone can share that would be great, thanks!
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1.L. Thomas, G. Jan, S. Le, and P.-K. Wang, Appl. Phys. Lett. 106, 162402
(2015)
2.Enhanced spin-torque in double tunnel junctions using a nonmagnetic-metal spacer
Download PDF
C. H. Chen1, Y. H. Cheng1, C. W. Ko1 and W. J. Hsueh1,a)
Enhancement of Spin-transfer torque switching via resonant tunneling
Appl. Phys. Lett. 105, 232410 (2014); 10.1063/1.4904408
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In TMR or Spin-Valve structure most of the cases Synthetic Antiferromagnetic layer (SAF) is been used as a reference or pinned layer. What advantages it provides over conventional layer consisting only AFM/FM exchange bias?  
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You need no additional target material like PtMn with its sophisticated annealing demands and can control pinning strength only by choosing the right thicknesses for interlayer and material thickness -  nevertheless the need of high accuracy in deposition of the nm-thick layers is to be estimated as challenging, too.
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Non-locality is a curious feature, yet essentially a quantum attribute that is linked to the violation of Bell inequality of any form. It arises from the impossibility of simultaneous joint measurements of observables. The Clauser-Horne-Shimony-Holt (CHSH) inequality is the only extremal Bell inequality with two settings and two outcomes per site. This inequality provides a basis to compare predictions of quantum theories with those linked local realism.
During non-Markovian dynamics of open quantum systems, there is break down of the well known Markovian model. This may occur due to strong system-environment coupling or when un-factorized initial conditions exist between the system and environment. Notably, a statistical interpretation of the density matrix is not defined for non-Markovian evolution.
My question is: Is there increased non-locality when a system undergoes non-Markovian dynamics and if so, how can this be quantified. I used the word "increased" because non-locality may be present in the case of Markovian dynamics, and the query focusses on whether certain aspects  of  non-Markovian dynamics accentuates non-locality.
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@Leyvraz  Non-Markovianity has been linked quantitatively to different distance measures (e.g., trace distance, Bures distance, Hilbert-Schmidt distance). However these measures vary  due to inherently differet characteristics,  and as such there is no  unique definition of non-Markovianity in quantum systems. In a sense, if there is a measure that responds to deviations from the continuous, memoryless, completely positive semi-group feature of Markovian evolution, then it is may qualify as a tool to quantify non-Markovianity. The concepts of divisibility and distinguishability  have been very useful  in identifying  measures which violate the complete positivity during the evolution of a  system. So to answer your question: there is no single quantity that I have in mind.....as long as "it" is linked to the breakdown of the complete positivity during  evolution, it will do ok. Even the increase of trace distance during time intervals (for instance) may be  taken as a sufficient but not necessary signature of  non-Markovianity. This shows the complexities of non-Markovian dynamics.
It is challenging as well to quantify Non-locality, and there are attempts to involve  the  Bell inequality and variations thereof  to quantify the boundaries of non-local events. So we have hurdles in defining the problem even before resorting to solving it!
Perhaps it is a good start to seek a link (implicit or otherwise) between non-Markovianity and non-locality. To this end, it would be interesting to seek  the role of mathematical mappings known as the assignment or extension maps within the context of this problem. Assignment maps provide description as to how a subsystem is embedded within a larger system. These maps can take on negative values in some instances, and the  quantum system proceeds to evolve with signatures of non-Markovian dynamics for a given period of time. Will further examination of the Assignment maps help establish a link  between increased non-Markovianity and non-locality? What is the role of the Minkowski space & geometric algebra in this regard? Are they better platforms with which to examine this problem, which appears ill defined at the moment.
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During reading of GMR, I slightly got confused. Some authors reveals that when spin up electron passes through parallel configuration (spin up) it is scattered while spin down electron passes without scattering.
Some shows that spin down electrons get scattered while the electron with parallel spin (spin up) does not get scattered.
What is the real mechanism?
Could anyone explain me?
I am attaching two figure taken from the literature.
Thanks
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The general concept is when the two electrodes have parallel spin orientation (i.e. the external magnetic field is more than the coercive fields of both the electrodes and the spins are aligned in the direction of the applied magnetic field) then any one spin channel will suffer higher scattering and one will not be scattered in any of the two electrodes. This is the low resistance state (in case of normal GMR or TMR). For intermediate applied magnetic field, i.e when the field value is in between the two coercive field values, the two electrodes have spins aligned anti-parallel to each other and then both spin channels will suffer scaterring in either of the electrodes giving higher resistance state. Reverse is the case in case of inverse GMR or TMR. You can have a look at this book chapter for details on the fundamentals: 
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Could someone explain in simple way the difference between spin pumping and spin injection in spintronics?
Thanks !
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I am trying to analyze the domain pattern of the demagnetized state of a ferromagnetic sample to obtain information regarding domain wall width and energy density. For that after demagnetization, I am trying to do a 2D FFT of the image pattern and obtain the amplitude of the FFT pattern. Can anyone suggest some literatures on how to use the FFT to obtain the useful parameters. My problem is that I do not know how to analyze the FFT pattern other than the formula of obtaining the domain wall energy density
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The FFT looks pretty much isotropicyou can then e.g. generate a radial distribution function from it.
Btw: the plot you shared: is it the real part of the FFT or is it the power spectrum?
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I am trying to see if there are other methods than hall probe or NMR probe to measure magnetic fields.
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Names can be misleading relates primarily to the measurement surface area
GMR for small fields
SMR for high fields
see,for
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Parity doublet means two orbital with opposite parities with different orbital angular momenta lies close to each other. Parity doublet is only seen in the case of largedeformed nuclei not in spherical nuclei. In spherical nuclei, these orbital is very  far from each other.
In 1997, Ginocchio showed that the psedospin symmetry in nuclei is exactly conserved when the scalar potential S(r) and the vector potential V(r) have the same size but opposite spin i.e. sigma(r)=S(r)+V(r)=0. This discoveries not only reveals the origin of the pseudospin symmetry but also demostreted an unexpected succes of the RMF theory. The psedospin symmetries is much better for exotic nuclei with a highly diffused potential. In the case of pseudospin doublet , the energy levels spliting with two different orbital angular momenta but same angular momentum(j). In the pseudospin doublet is only persist in the case of deformed nuclei not in spherical nuclei . Can any body clear the difference between these parity doublet and pseudospin doublet. Is there same or different?
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Pseudospin symmetry should imply exact (and perhaps higher than doublet) degeneracy.
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If (muSR) vs time is straight line with small slope what does that mean?
should we look Zero Field only or F ONE?
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It is difficult to provide an definitive answer to the question if the type of system being studied is not known. Assuming this is a magnetic material, if the muSR spectrum is a straight line with small slope, this suggests you have an exponential relaxation P_Z(t) = \exp(-\lambda t) with a small relaxation rate: indeed if \lambda t << 1, \exp(-\lambda t) = 1 - \lambda t. The presence of muon spin relaxation implies there is an exchange of energy between the muon and the system being studied. The Zeeman energy of the muon spin being extremely small  on the scale of k_B T, it means there is essentially no gap in the system.
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The rhombograms for the effective g-factors of Fe(III) allow to calculate these factors knowing the rhombicity E/D parameter and viceversa. But are there analytical formulas (perturbative for example) for these g-factors? In W. Hagen's book "Biomolecular EPR spectroscopy" it appears that there are not analytical formulas, except for low E/D ratios. If someone could point me to any bibliography where these are derived I would appreciate it.
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I may be wrong but this is my take on it:
a "free" S=5/2 system of d-electrons means a d^5 configuration: every d-orbital is occupied once, all have their spins parallel, it's a pure spin system, no orbital contribution to the magnetic moment and hence g=g0.
If your system isn't like this, it means that you have some (small but finite) configurational admixture of other spin states (of which S=3/2 will be of lowest energy). This part of the state now does have finite ligand/crystal field splitting and spin orbit coupling (soc), and this combination is what gives rise to a variation in g-factor. In general, the g-factor becomes anisotropic as a result.
I can only guess that one cand find a relationship between ligand/crystal field and what you denote as rhombicity. For d-electron-systems, the ligand field term is usually way strongest, so that spin orbit coupling can be treated as a perturbation. But a perturbation to what? The easiest cases would be those of spherical or at least cubic symmetry. Deviation from those then have also to be treated as perturbation. You have then two perturbation terms of different character, and the way/amount to which soc intervenes in the results depends on the amount of distortion (rhombicity). I have no difficulty in believing that this can only work in the limit of small distortion.
And perturbation theory anyway implies that the departure from the reference (unperturbed) state is small.
Mathematically you may think of this as follows: think of a basis set of states of the mixed configuration, symbolically represented as below
{ ams * |S=5/2, mS=-5/2...5/2> + bms' * |S'=3/2, mS'=-3/2...3/2> }
Zeeman energy, ligand field and spin orbit coupling are the ingredients to the total Hamiltonian the electrons are subject to. These do not commute, in general and therefore have no common set of eigenstates. To obtain the energies of all states (and the g-factor is in the energy differences of the lowest energy states at small fields) you would have to diagonalize the total Hamiltonian (compute eigenvalues and eigenvectors of the Hamiltonian). You therefore have to find the roots of the characteristic polynomial of the matrix representing the Hamiltonian. As soon as there are more than 4 states, there is no analalytical solution for the roots of that polynomial, you have to solve the thing numerically.
In perturbation theory of first order, you just consider the effect of the different terms on the diagonal elements of that matrix (instead of diagonalizing it). "Energies change but the states don't" in this approximation. For this to be correct, the states chosen as the basis in which the Hamiltonian is represented need to be as close as possible to the 'true' ones. You cannot afford large deviations. Getting back to your question: if the reference state for the g-factor formulae is one with zero rhombicity, perturbation theory for the Zeeman energy (-> g-factor) gets out of control if the rhombicity gets too large.
Sorry for the long post. And no, I have no suitable reference at hand to recommend.
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I am a little confused with these two terminologies. It seems that both of them can show high resistance to perticular spin, so what is the difference between a spen filter and a spin valve?
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The term spin valve refers to a tunnel magneto resistance trillayer system where two ferromagnets are separated by a non-magnetic insulating barrier and the relative orientation of the magnetization determines the tunnel magnetoresistance. In a spin filter, the barrier material itself is a ferromagnetic insulator. The orientation of the magnetization in the tunneling barrier allows for changes in the barrier height between spin up and spin down.  
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As far my understanding tells, a BMP is a particular type of molecule-complex in an occupied donor or an acceptor. Bound electrons (holes) trapped by the defect states can couple with the available d/f shell ions within a hydrogenic Bohr orbit of radius rH (rH ~ 0.76 nm) and form BMP through the sp-d interaction leading to a net ferromagnetic alignment of the magnetic spins. Through the percolation of the BMPs, a long range FM ordering can occur in case of the materials like magnetic semiconducting material and other diluted magnetic materials where the concentrations of d-shell electrons and itinerant carriers are quite less as compared to the FM metals or their alloys.
Can anybody share detailed ideas on this regard, about the preferable conditions of BMP formation and their percolation to produce High temperature FM characteristics (like the required conditions of the donar/acceptor defect states, free carriers, concentration of d/f electrons, BMP concentration, order of magnetic moment etc.). Particularly, incase of 'Magnetic Semiconductor' materials.
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You can get the similar or apropriate answer by searching the keyword in the GOOGLE SCHOLAR page. Usually you will get the first paper similar to your keyword.
From my experience, this way will help you a lot. If you still have a problem, do not hasitate to let me know.
Kind regards, Dr ZOL BAHRI - Universiti Malaysia Perlis, MALAYSIA
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I mean i have come across a few definitions and they all give me different results and I have gotten really confused over it and don't know which one to use.So I am awaiting for someone to come forward and clear the air over it for once and all.
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The TMR effect is approximated by Julliere’s formula,
TMR = [(RAP – RP)/RP]∗ 100% = 2P1P2/(1 − P1P2)
where RAP and RP are the tunnel barrier resistance for antiparallel and parallel aligned magnetic moments of the two electrodes and P1 and P2 indicate the spin polarization of the electrodes. The latter quantity is often specified as
P = [N (EF)− N(EF)]/[N (EF) + N(EF)]
with N and N indicating the density of majority and minority electrons at the Fermi level.
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There are many reports on defect related ferromagnetism in Oxide materials. Also its saturation moment is quite low and it varies a lot depending on the growth process. So is it possible to use it in the spintronic device applications in a controlled way?
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The existence of d0 magnetism has not not been proved beyond doubt. So its application in spintronics is just a fantasy!
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Half-Metallic compounds
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Thank You @Shaban Ahmed Ali Abdel-Raheem
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COMSOL tool is suitable?
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Hi, Venkat Thanks. I have found so many Micromagnetic Simulators, but, was confused which one is the best. Actually, I am looking for simulation of the Organic Spintronic devices. Can you comment on COMSOL or ATOMISTIX (ATK) simulator?
Thanks again.......
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In my experiment on spintronics oscillators I recorded Power Spectral Density (PSD)/Bandwidth as a function of frequency (using Spectrum Analyzer). I have corrected the background subtraction of our data. I considered data for I_dc = 0.0 mA as the background data. Moreover we have not used any preamplifier except the internal-preamplifier of the spectrum analyzer. As far as I know the gain of internal-preamplifier need not be corrected as it is automatically corrected being internal component of the Spectrum analyzer.For a particular dc current (I_dc), I added up all the PSDs at different frequencies and then calculated emitted microwave power of oscillator for constant (I_dc) by following formula:
Emitted Microwave Power  = (Total PSD/Bandwidth) * Frequency range
Am I correct while calculating the emitted power?
Please give your comments.
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Dear DINESH,
It is my pleasure to introduce some help to you. I am sorry for the late return to the question. You can revert to this outstanding book: digital communications by Iva Glover and Peter Grant,. Especially chapter two will be useful to you.
wish you success
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Electrons have both charge and spin. Spin polarization is needed for a spin current.
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The thing is scattering by phonons. With such a scattering of spin is not conserved. And since such scattering by phonons is the main mechanism for resistance, the spin is not conserved.
In principle, if the state at the Fermi level would be spin-polarized, that is, if the electron energy is dependent on the direction of the spin, then one would expect the spin conservation when current flows. However, such materials are extremely rare. I know of only two examples of this Heusler alloys and materials based on chromium dichalcogenides such solid solutions of substitution CrxTi1-xSe2.
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I'm looking for some zero-moment half metals which have potential application in spintronic devices.
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A zero moment half-metal seems a contradiction in terms. If it is a metal, there is finite Density of States at the Fermi energy, and if it is a halfmetal, only one spin band is involved. Since this band is not fully occupied, its total spin is not fully compensated. The band can have a low moment but not a zero moment.
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Your help is highly appreciative as I am looking to work on CPP-GMR devices. 
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Dear Sayani,
Thank you very much for your interest. Yep I am working under the supervision of Prof. K. G. suresh. I have some idea about Heusler alloys based CPP-GMR devices because I worked in Prof. Hono group (NIMS Japan) for 3 months.
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Kindly tell me in detail about the possible outcomes of the "Anomalous Hall Effect" measurement. 
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A simple answer would go like this. The ordinary Hall effect in semiconductors appears in response to an applied magnetic field. The drifting charge carriers experience a Lorentz force in the presence of an applied field and thus accumulate on one side of the sample to create a Hall-voltage. It is now almost intuitive that a sample that is magnetized even in the absence of a magnetic field will create a Hall-voltage as well. This Hall-effect which appears in the absence of an applied magnetic field is the anomalous Hall effect. Obviously one can learn about the magnetism/spin-polarization of the sample through such measurements. It is tempting to say that the anomalous Hall effect originates from the internal field that accompanies the magnetization and thus is basically similar to the ordinary Hall effect. However, this is not true. The actual microscopic mechanism is different, depends on spin orbit coupling and spin dependent scattering.  
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Multiferroics and Spintronics
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“g” values are dependent on L,S, J and Spin Orbit Coupling* [SOC](λ complex ). SOC it is an important factor which can make the value of “g” to VARY FROM THEIR THEORETICAL VALUES.
First about THEORETICAL VALUE OF “g” .
Theoretically:
g =1+ [(J(J+1)+S(S+1) –L(L+1) ]/ [2J(J+1)] -------(I)
We can divide the discussion on the calculation of theoretical “g” values in three parts.
[A] In case of free electron ,L=0.
{ J values lie in between [J=L-S], [L-S+1]---------[L+S]( Modulas)]
So J=S=I/2.
Putting these values of J and S in the above relation;
g =2.0.
[B] In almost all the ORGANIC FREE RADICALS, L=0 .So”g” value should come out to almost equal to 2. But, it is ,generally, taken to be 2.0023; the 0.0023 being the relativistic correction (Discussion of this correction omitted intentionally).
[C]Now ESR of the paramagnetic complexes. Here the unpaired electron is spread over whole of the paramagnetic complexes( transition , lanthanides and actinide ions) with the central ion genally possessing non zero value of L. So “g” can be MORE as well as LESS THAN 2.In order to prove the point, I intentionally take a case where “g” is in fractions as:
Ce^3 ,with outermost configuration 4f^1, has maximum L value is =3 .With one unpaired electron, its max S=1/2. So its J= 3-1/2=5/2.
Put these L, S and J values in (I) to obtain g=6/7.
[D] SOC and “ g “ relation:
We know the the electron has two types of motions- the “spin motion” and the “orbital motion”, Both these motions cobtribute to the magnetism. Of course, the contribution from “spin motion” is much more than the “orbital motion”. The SOC(λ complex) may RESTRICT the “orbital motion” either COMPLETELY or PARTIALLY or even MAY NOT RESTRICT AT ALL. The terms used are COMPLETE QUENCHING, PARTIAL QUENCHING or NO QUENCHING** of the orbital motion respectively. This, in simple sense, means that the value of L may differ thom the theoretically calculated values of L.So the relation(I) does not hold good for the complexes.
Depending upon the ground term [A or E or T ] of the transtion metal ion , the following relations can be given to show as how the “g” and SOC are mutally related :
[1] When transition metal ion has “A” ground term:
g= 2.0(1-4 λ complex/ 10Dq) -----------(II)
[1I] When transition metal ion has “E” ground term:
g= 2.0(1-2 λ complex/ 10Dq) ------------(III)
[III] Different relations are reported for “T” terms if the terms differ in multiplicity.
[E] Lastly:
One very important point which needs to be taken into consideration is that:
λcomplex is positive when the “d” sub shell is less than half full( d^1-d^4) but is negative if the “d” sub shell is more than half full( d^6-d^9). Accordingly, the values of “g” will be less in complexes with metal ions with configuration-d^1-d^4.The reverse will be observed in the metal ion complexes with d^6-d^9 configurations.
*λcomplex have different values for different complexes of even the same metal ion.
** There are certain rules which need separate discussion.
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I am trying to do RF sputtering for MgO at lowest possible pressure. With the same conditions (i.e. same power supply, chamber, base vaccum, cooling water, sputtering gun) I am seeing a consistent increase in the Lowest sputtering Pressrue for my MgO, I even recently ordered the same target from the same company to make sure it is not target degradation but did not help (the same as old target). I do not see this change for any other targets I have. I was wondering if anyone has any thought . 
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MgO is known to release a lot of water vapour, It might be that as you deposit the residul partial pressure from water may cause your deposition pressure to increase, try presputtering for longer (30 mins) prior to growth. Let me know if it works.
 
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I am having problems with my samples showing not expected resistance. I do use photolithography to pattern them and ion etching to etch them (size of samples are about 50-200 microns, there are different sizes on the pattern) .from my resistance measurements, I only see very few (5-10%) of the samples are showing the expected values for resistance and the majority of them show very low resistance (and all almost the same value). I am wondering what is happening because the good samples are scattered almost randomly across the entire film and there is no correlation between their positions.
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Hi Hamid,
Given the nature of the multilayers you are trying to etch I guess you are dealing with thin even ultra-thin layers (so that the 50-200 um are lateral dimensions, right?). I also suppose you are using the resist itself as a mask during the etching process with Ar plasma (right?)
Depending on the thermal stability of the resist you use and on the pre/post-baking you perform on the resist, it may suffer some hardening, becoming sometimes impossible to remove.
Have you considered to add a step to your protocole and use an Al mask instead? An Al mask is quite easy to etch (known etching rate) and to remove afterwards. For instance, in order to etch e-beam defined structures on a layer:
Ta (3) / Cu (2) / IrMn (6) / Co65Fe35 (2.5) / Cu (3) / Co65Fe35 (4) / Ni86Fe14 (15) /Ru (6)
I used an 80 nm Al mask to perform ion etching under Ar plasma, and the remove the left Al with the solution MF319.