Spintronics - Science topic

Hello, Dear Professor!

I have experience in the fields of condensed matter physics (together in quantum base and material theory), material chemistry and also XPS. During the synthesis of the novel layers and coatings, I use different official XPS databases with widespread journal links. So we could try to interpret some spectral lines and other concomitant parameters. If this offer is interesting, you also can obtain my some works in this area in my ResearchGate profile. Moreover, there is my ORCID page: https://orcid.org/0000-0001-5957-4525

Thank you for attention!

Best wishes,

PhD, Associate Professor

A. Berezner

E-mail: a.berezner1009@gmail.com

Spin Transfer Torque Nano Oscillators (STNOs) and Spin Hall Nano Oscillators (SHNOs) are magnetic nano oscillators driven by spin currents. Still, they differ in how they generate and utilize this spin current.

In summary, the main difference between STNOs and SHNOs lies in the spin current generation and injection method. STNOs inject the spin current directly into the magnetic layer, while SHNOs use the Spin Hall effect to generate a transverse spin current. This can result in differences in efficiency, tunability, and integration possibilities.

Dear Supriya Raut ,

ESR spectroscopy is a powerful technique used to study the properties of unpaired electrons, and it has applications in quantum mechanics, including the investigation of quantum behavior and magnetic properties of materials, as well as in spintronics for characterizing spin-dependent transport properties of materials.

In spintronics, ESR plays a crucial role in characterizing spin-dependent transport properties of materials, such as spin-polarized currents and spin injection. Spintronics is a field that aims to exploit the quantum mechanical properties of electron spin for the development of new electronic devices. ESR spectroscopy is used to investigate spin transport properties in various types of materials, such as ferromagnetic metals, semiconductors, and organic materials. By understanding the spin transport properties of these materials, researchers can develop new materials and devices that exploit spin for information processing and storage.

Hope this helps you.

Regards,

KP

Dear Prof. Robin Singla

In addition to the right answer by Prof. Xavier Oudet , I can advice to check the monograph by Frederick Reif "Fundamentals of Statistical and Thermal Physics", McGraw Hill, 1965

First chapters are based on the analysis of a total magnetic moment M with lots of examples worked out for different cases from the perspective of Statistical Mechanics methods of distribution (binomial and gaussian).

Kind Regards.

The read head of your computer's HDD since over 20 years...

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.

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.

The question is very interesting, thank you, Dear Bhargab Kakati

Probably the citing references to the following research article could have a partial answer, unfortunately, I do not have access to it.

Best Regards.

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).

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.

📷

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.

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.

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

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.

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

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

Dear Shalu Pathak,

Please look at the introduction of the following paper for the difference between TRS and inversion symmetry first :

In valleytronics, there are several open discussion on TRS, you can check-in:

If one of the two symmetries, in this case, the TRS is preserved, and the inversion not, the states are not protected, as in the case of valleytronics, please check:

Check-in addition to the following external lecture, the part on Kramers degeneracy, one should remember that spin-orbit coupling might or not play a role here:

Dear Raghvendra Posti ,

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:

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

Yes definitely, see e.g.,

Dear Prof. Thiruvengadam Vijayabaskaran, in addition to the answer provided by Prof. Mohammad Saeed Bahramy, I can add that for conduction electrons in normal metals, the v_rsm velocity is ~ 10⁵ m/s (Au, Ag) (Drude model value) which is a non-relativistic value.

The drift velocity is even smaller ~ 10^-5 m/s for Cu and happens with an applied external E field. So in terms of physical kinetic properties, conduction electrons velocity in normal metals is a non-relativistic quantity.

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.

read this paper

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.

Dear Prof. Dr Aga Shahee

Your question is interesting & quite relevant, henceforth I will try to answer partially your question in a couple of posts in your thread:

A sound velocity anomaly can be directly calculated by means of Ehrenfest relations for 2^nd order phase transitions-PT. For instance a jump in sound velocity can be calculated at the superconducting transition temperature T_c. This is an anomaly that have been observed in some materials. See [1] for example to have a better idea, but I can refer to some specific literature if you wish.

[1] https://www.worldscientific.com/doi/pdf/10.1142/9789813274181_0001

This is part of the question, but what I cannot do now is to relate the jump to an structural phase transition which I guess is a 1^st order PT [2] quoting & is associated with a dynamical instability by the soft mode. According to some authors [3] a physical explanation will be "...the soft mode happens when cooling a material from a temperature above T_c, a normal mode of vibration of the crystal decreases to 0 freq when the crystal becomes unstable & distorts to a new structure..."

[2] https://arxiv.org/ftp/arxiv/papers/1102/1102.1085.pdf

[3] https://arxiv.org/ftp/cond-mat/papers/0605/0605489.pdf

Finally, respect to lattice degrees of freedom showing divergence, I guess this is what happens to 1D systems (according to Peierls & Landau [4]), isn´t it?

[4] https://en.wikipedia.org/wiki/Peierls_transition

You can follow

I think, the materials have wide band gap is important when these materials are strained

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.

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.

Hello, there use this

iop(3/33=4) pop=full, it will show you the overlap matrix

Regards

Ajay Khanna

Please check out our website:

Please check out our website:

You should read the following article to get some initial knowledge about spin current.

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.

see for example:

Structural, electronic and magnetic properties of Fe, Co, Mn-doped GaN and ZnO diluted magnetic semiconductors

A. Alsaad

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)

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? 

Thanks Dr. Arnab Roy

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".

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).

[4] S. Schwalbe et al., https://www.researchgate.net/publication/305615774_Ab_initio_electronic_structure_and_optical_conductivity_of_bismuth_tellurohalides

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)

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.

Thanks :D

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.

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.

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

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.

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.

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.

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.

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.

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.

You might find this link useful:

 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.

it depends in your growth system. 

If you clarify it more we can help

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.

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

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.

@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.

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: 

The following address may be helpful.

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?

Names can be misleading relates primarily to the measurement surface area

GMR for small fields

SMR for high fields

see,for

Pseudospin symmetry should imply exact (and perhaps higher than doublet) degeneracy.

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.

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

{ a_ms * |S=5/2, m_S=-5/2...5/2> + b_ms' * |S'=3/2, m_S'=-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.

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.  

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

The TMR effect is approximated by Julliere’s formula,

TMR = [(R_AP – R_P)/R_P]∗ 100% = 2P₁P^₂/(1 − P₁P₂)

where R_AP and R_P 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_↑ (E_F)− N_↓(E_F)]/[N_↑ (E_F) + N_↓(E_F)]

with N_↑ and N_↓ indicating the density of majority and minority electrons at the Fermi level.

The existence of d0 magnetism has not not been proved beyond doubt. So its application in spintronics is just a fantasy!

Thank You @Shaban Ahmed Ali Abdel-Raheem

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.......

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

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.