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Nonreciprocity engineering in magnetostatic spin waves
Abstract
Magnetostatic surface spin waves (MSSW) excited from a coplanar waveguide
antenna travel in different directions with different amplitudes. This effect,
called nonreciprocity of MSSW, has been investigated by micromagnetic
simulations. The ratio of amplitude of two counter propagating spin waves, the
nonreciprocity parameter {\kappa}, is obtained for different ferromagnetic
materials, such as NiFe (Py), CoFeAl, yttrium iron garnet (YIG), and GaMnAs. A
device schematic has been proposed in which {\kappa} can be tuned to a large
value by varying simple geometrical parameters of the device.
... The amplitude of the MSSW signal depends on the relative directions of the magnetization (M) of the material and the spin wave wave-vector (k). A clear non-reciprocal behaviour of spin waves is known to exist for opposite signs of wave-vectors (±k) or bias field (±H b ), as shown in figure 2(c) [15,19,30,31], and the non-reciprocity factor (κ), defined as κ = A (H b+ ) /A (H b− ), is a function of the bias field as shown in figure 2(d) similar to electrical measurements of surface spin waves [13]. The higher temporal resolution of TRSKM as compared with BLS measurements makes it a suitable measurement technique to confirm previous findings on the non-reciprocal behaviour of spin wave dynamics in the time domain. ...
... The non-reciprocity in figures 2(c) and (d) is evaluated at a distance of 10 µm from the stripline. The non-reciprocal behaviour arises as a result of the asymmetric distribution of the out-of-plane component of the excitation field (h z ) on either side of the stripline [15,31]. The in-plane component of the excitation field (h y ) retains the same phase across the stripline, while h z undergoes a phase change of π. ...
... As a result, the spin waves excited due to in-phase h y and h z fields (on one side of the stripline) are stronger than those excited by out-of-phase h y and h z fields (on the opposite side of the stripline), resulting in the non-reciprocity of spin waves. The magnitude of κ is of the same order as previously reported [30,31], and can be tuned by adjusting the width and thickness of the stripline which controls the excitation field (h y,z ). This phenomenon has promising potential in the field of logic devices to represent binary states of '1' and '0', as has been recently proposed [13]. ...
We have studied the propagation characteristics of spin wave modes in a
permalloy stripe by time-resolved magneto-optical Kerr effect techniques. We
observe a beating interference pattern in the time domain under the influence
of an electrical square pulse excitation at the center of the stripe. We also
probe the non-reciprocal behavior of propagating spin waves with a dependence
on the external magnetic field. Spatial dependence studies show that localized
edge mode spin waves have a lower frequency than spin waves in the center of
the stripe, due to the varying magnetization vector across the width of the
stripe.
... The specific property of the nonreciprocity might be a benefit for the enhancement of logic circuits based on magnetic waveguide. Therefore, the characterization and tuning of the nonreciprocity in magnonics has been intensively investigated (20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31), including the relation between the nonreciprocity and spin pumping (32) or Dzyaloshinskii-Moriya interaction (33,34). The nonreciprocity, due to its intrinsic characteristic in the magnetostatic surface wave (MSSW) mode (35), together with Joule-heat-free transport in GHz-frequencies (30) and compatibility with the spin Hall current system (36,37) makes spin wave one of the promising candidates for future data carriers. ...
... In order to confirm the spin pumping effect, we have performed the ferromagnetic resonance (FMR) measurements with the same devices of the spin pumping measurements. Taking the spin pumping effect into account, the presence of Ta layer enhances the damping parameter of Py above the intrinsic value (45,46), It must be noted that our observations are different from the earlier reports on spin wave nonreciprocity studied only in the MSSW mode (22,23,26,28). In order to compare our results with the MSSW mode, we have also measured the nonreciprocity value with sweeping in-plane magnetic field, Hy. ...
Spin waves are propagating disturbances in the magnetization of magnetic materials. One of their interesting properties is the nonreciprocity, exhibiting that their amplitude depends on the magnetization direction. Nonreciprocity in spin waves is of great interest in both fundamental science and applications, as it offers an extra knob to control the flow of waves for the technological fields of logics and switch applications. We show a high nonreciprocity in spin waves from Ta/Py bilayer systems with out-of-plane magnetic fields. The nonreciprocity depends on the thickness of Ta underlayer which is found to induce an interfacial anisotropy. The origin of observed high nonreciprocity is twofold; different polarities of the in-plane magnetization due to different angles of canted out-of-plane anisotropy and the spin pumping effect at the Ta/Py interface. Our findings provide an opportunity to engineer highly efficient nonreciprocal spin wave based applications such as nonreciprocal microwave devices, magnonic logic gates, and information transports.
... Aside from tailored spin wave dispersions, a practical approach for implementing nonreciprocal magnon propagation is given by specific geometries of antenna that can selectively excite a desired chirality of spin waves so that the antenna preferentially excites a spin wave propagating in one way compared to the opposite direction. 106,133,134 For example, an Oersted field generated from a current through a thin wire placed on top of a film has a definite chirality, i.e., the Oersted field rotates clockwise or counterclockwise as one moves perpendicular to the wire in the film, and this chirality will be reversed if one moves the wire from above the film to below the film. Therefore, the Oersted field excites only one set of spin waves with the same chirality, or the same propagation direction, much more efficiently compared to the other. ...
... Therefore, the Oersted field excites only one set of spin waves with the same chirality, or the same propagation direction, much more efficiently compared to the other. 133 The same mechanism also applies to the coplanar waveguide (CPW) geometry. 135 Figure 5 time-varying Oersted field has the same chirality as that of the timevarying component of the magnetization of a spin wave propagating at the Àx direction as one can see in Fig. 5(b), i.e., both vectors rotate counterclockwise as one sweeps the coordinate to the þx direction. ...
Magnons, the quanta of collective spin excitations in magnetically ordered materials, have distinct properties that make them uniquely appealing for quantum information applications. They can have ultra-small wavelengths down to the nanometer scale even at microwave frequencies. They can provide coupling to a diverse set of other quantum excitations, and their inherently gyrotropic dynamics forms the basis for pronounced nonreciprocities. In this article, we discuss what the current research challenges are for integrating magnetic materials into quantum information systems and provide a perspective on how to address them.
... [7][8][9] Because of their special dispersion relations, 10 magnons support short-wavelength excitations down to nanometer scale at microwave bandwidth [11][12][13][14][15][16] along with superior frequency tunability with an external magnetic field. In addition, magnons exhibit nonreciprocity based on many unique properties of magnetic excitations, including intrinsic chirality selection in propagating magnetostatic surface spin waves (MSSW), [17][18][19][20][21][22][23][24] wavevector-dependent spin wave dispersion shifting, [25][26][27][28][29][30][31][32][33][34][35][36][37] and non-Hermitian circuit engineering. [38][39][40] This allows for compact integration of miniaturized, broad-band, and highly tunable isolators in microwave circuits. ...
... 45,46 However, as the film thickness is decreased down to nanometer levels, the surface waves will permeate to the entire thickness and be both excited by antennas at the top surface, leading to suppressed isolation that is typically less than 10 dB. 20 Alternatively, spin wave nonreciprocity can be achieved by chirality selection from well-designed microwave antennas, 22,47,48 where þk and -k MSSWs exhibit clockwise and counterclockwise mode profiles depending on the orientation of the magnetization vector, respectively. This technique is not restricted by the film thickness and, thus, can be applied for highly efficient spin wave isolation with the proper geometric design. ...
Nonreciprocal magnon propagation has recently become a highly potential approach of developing chip-embedded microwave isolators for advanced information processing. However, it is challenging to achieve large nonreciprocity in miniaturized magnetic thin-film devices because of the difficulty of distinguishing propagating surface spin waves along the opposite directions when the film thickness is small. In this work, we experimentally realize unidirectional microwave transduction with sub-micrometer-wavelength propagating magnons in a yttrium iron garnet (YIG) thin-film delay line. We achieve a non-decaying isolation of 30 dB with a broad field-tunable bandpass frequency range up to 14 GHz. The large isolation is due to the selection of chiral magnetostatic surface spin waves with the Oersted field generated from the coplanar waveguide antenna. Increasing the geometry ratio between the antenna width and YIG thickness drastically reduces the nonreciprocity and introduces additional magnon transmission bands. Our results pave the way for on-chip microwave isolation and tunable delay line with short-wavelength magnonic excitations.
... Aside from tailored spin wave dispersion, a practical approach for implementing nonreciprocal magnon propagation is given by specific geometries of antenna that can selectively excite a desired chirality of spin waves so that the antenna preferentially excites a spin wave propagating in one way compared to opposite direction 105,132,133 . For example, an Oersted field generated from a current through a thin wire placed on top of a film has a definite chirality, i.e., the Oersted field rotates clockwise or counter-clockwise as one moves perpendicular to the wire in the film and this chirality will be reversed if one moves the wire from above the film to below the film. ...
... For example, an Oersted field generated from a current through a thin wire placed on top of a film has a definite chirality, i.e., the Oersted field rotates clockwise or counter-clockwise as one moves perpendicular to the wire in the film and this chirality will be reversed if one moves the wire from above the film to below the film. Therefore, the Oersted field excites only one set of spin waves with the same chirality, or the same propagating direction, much more efficiently compared to the other 132 . The same mechanism also applies to the coplanar waveguide (CPW) geometry 134 . ...
Magnons, the quanta of collective spin excitations in magnetically ordered materials, have distinct properties that make them uniquely appealing for quantum information applications. They can have ultra-small wavelengths down to the nanometer scale even at microwave frequencies. They can provide coupling to a diverse set of other quantum excitations, and their inherently gyrotropic dynamics forms the basis for pronounced non-reciprocities. In this article we discuss what the current research challenges are for integrating magnetic materials into quantum information systems and provide a perspective on how to address them.
... Thus, spin wave nonreciprocity can provide additional degrees of freedom for the control of signal propagation 13-17 . Spin wave nonreciprocity has large potential for applications in switches and logic devices due to selectively unidirectional spin wave propagation 12,18 , while in devices that require bidirectional signal propagation, the spin wave intensity should be the same in both directions 19 . ...
... The intensity difference is likely due to asymmetric field application, induced by the antenna, which is also www.nature.com/scientificreports/ observed in other studies 15,16,19 . Thus, the characteristics in sample B cannot be utilized for the control of asymmetric spin wave excitation and propagation, as reported in previous research 16 . ...
Asymmetric spin wave excitation and propagation are key properties to develop spin-based electronics, such as magnetic memory, spin information and logic devices. To date, such nonreciprocal effects cannot be manipulated in a system because of the geometrical magnetic configuration, while large values of asymmetry ratio are achieved. In this study, we suggest a new magnetic system with two blocks, in which the asymmetric intensity ratio can be changed between 0.276 and 1.43 by adjusting the excitation frequency between 7.8 GHz and 9.4 GHz. Because the two blocks have different widths, they have their own spin wave excitation frequency ranges. Indeed, the spin wave intensities in the two blocks, detected by the Brillouin light scattering spectrum, were observed to be frequency-dependent, yielding tuneable asymmetry ratio. Thus, this study provides a new path to enhance the application of spin waves in spin-based electronics.
... We applied the total non-reflection effect on only a few of antidots in a plane YIG film to create a strong SW beam. To switch the direction of the beam we used the effect of non-reciprocal excitation of the surface spin waves by the microstrip antenna 18,41 . Moreover, we demonstrate by the micromagnetic simulations (MS) and iso-frequency curve method that the formation of a strong SW beam results from the refraction of SWs near the antidots in an area in which the internal magnetic field is reduced by the demagnetizing field. ...
... This component oscillates in antiphase on the two sides of the antenna, and is responsible for the changing of the SW propagation direction on reversal of the magnetic field 43 . The difference of SW intensities between SWs emitted on opposite sides of the microstripe obtained in MS is similar to the measured values, and reach 10, according with the literature data 41,44 . The result of simulations, a high-intensity narrow SWs beam propagating along the line of antidots, with an amplitude much larger than that of the incident plane SW is visible in Fig. 6(a). ...
The application of spin waves in communication with information encoded in amplitude and phase could replace or enhance existing microelectronic and microwave devices with significantly decreased energy consumption. Spin waves (SW) are usually transported in a magnetic material shaped to act as a waveguide. However, the implementation of SW transport and switching in plane homogeneous magnetic films and running as a narrow beam with a small divergence angle still present a challenge. We propose a realization of a strong SW switchers based on a patterned yttrium iron garnet (YIG) film that could serve as a magnonic fundamental building block. Our concept relies on the creation of a narrow beam of relatively short-wavelength SW by effect of a total non-reflection, found to be tied to refraction on the decreasing internal magnetic field, near a line of antidots at YIG. Nonreciprocal SW excitation by a microstrip antenna is used for controlling the direction of the signal flow. We demonstrate unique features of the propagation of microwave-excited SW beams, provide insight into their physics and discuss their potential applications in high-frequency devices.
... Due to the existence of the Au ground layer, the MSSW at the top surface is different from the one propagating along the bottom surface, leading to the nonreciprocal effect. The measure of this nonreciprocity is characterized by the ratio of the amplitude and the phase difference between the two counterpropagating MSSWs [30], [38] NR − Amplitude = 20 log 10 ...
... It is worth mentioning that without placing a neighbor metallic layer, the origin of the nonreciprocity of the MSSW stems from either the constructive or destructive interference between the in-and out-plane components of the RF signals. In this case, the magnitude of the counterpropagating MSSWs is different, while the phase is preserved [38]. This is different from our results: by placing a metallic layer underneath the NiFe film, both the magnitude and the phase are changed. ...
Nonreciprocal spin wave propagation, induced by placing a neighboring metallic nonmagnetic layer, has been studied in metallic ferromagnetic thin films. The structure consists of a set of coupled microstrip transmission lines acting as antennas placed over a thin Ni₈₀Fe₂₀ layer. Nonreciprocal propagation of magnetostatic surface waves (MSSWs) has been observed. The nonreciprocal effect is evaluated by the amplitude ratio and the phase difference of the MSSWs traveling in opposite directions. By investigating the correlation between the device structure and the nonreciprocal effects, a maximum of -26.0 dB of the amplitude ratio and -180.0° phase difference were obtained. These results can be applied to optimize the nonreciprocal device.
... The specific property of the nonreciprocity might be a benefit for the enhancement of logic circuits based on magnetic waveguide. Therefore, the characterization and tuning of the nonreciprocity in magnonics has been intensively investigated (20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31), including the relation between the nonreciprocity and spin pumping (32) or Dzyaloshinskii-Moriya interaction (33,34). The nonreciprocity, due to its intrinsic characteristic in the magnetostatic surface wave (MSSW) mode (35), together with Joule-heat-free transport in GHz-frequencies (30) and compatibility with the spin Hall current system (36,37) makes spin wave one of the promising candidates for future data carriers. ...
... In order to confirm the spin pumping effect, we have performed the ferromagnetic resonance (FMR) measurements with the same devices of the spin pumping measurements. Taking the spin pumping effect into account, the presence of Ta layer enhances the damping parameter of Py above the intrinsic value (45,46), It must be noted that our observations are different from the earlier reports on spin wave nonreciprocity studied only in the MSSW mode (22,23,26,28). In order to compare our results with the MSSW mode, we have also measured the nonreciprocity value with sweeping in-plane magnetic field, Hy. ...
Spin waves are propagating disturbances in the magnetization of magnetic materials. One of their interesting properties is nonreciprocity, exhibiting that their amplitude depends on the magnetization direction. Nonreciprocity in spin waves is of great interest in both fundamental science and applications because it offers an extra knob to control the flow of waves for the technological fields of logics and switch applications. We show a high nonreciprocity in spin waves from Ta/Py bilayer systems with out-of-plane magnetic fields. The nonreciprocity depends on the thickness of Ta underlayer, which is found to induce an interfacial anisotropy. The origin of observed high nonreciprocity is twofold: different polarities of the in-plane magnetization due to different angles of canted out-of-plane anisotropy and the spin pumping effect at the Ta/Py interface. Our findings provide an opportunity to engineer highly efficient, nonreciprocal spin wave–based applications, such as nonreciprocal microwave devices, magnonic logic gates, and information transports.
... The dispersion relation and excitation of spin waves mainly depend on the direction of spin wave propagation with respect to the magnetization direction. Most of the magnetic materials used in spin wave studies have an in-planeoriented magnetic easy axis, for instance, magnetostatic spin waves (MSSW) in Permalloy (NiFe), CoFeAl ferromagnetic thin films [15], dipole-exchange spin waves in Fe-N thin films [16], and spin wave resonance investigation in half metallic ferromagnets [17]. The studies on characterization of spin wave propagation in nanometer-thick YIG thin films which have in-plane anisotropy (IPA) were carried out in [18,19]. ...
Magnetic insulating materials with perpendicular magnetic anisotropy bring an innovation to the existing spin-related technologies and magnonic applications. Yttrium iron garnet (YIG) stands out among other ferrimagnetic insulators due to its remarkable and unique properties. In this work, we represent perpendicular magnetic anisotropy (PMA) in relatively thick YIG films between 40 nm and 120 nm grown on Si (100) substrates. The strain at the interface of the Si substrate / YIG film promoted by the lattice mismatch resulted in a magnetic easy axis along the film normal. Excitation of standing spin wave modes within the films through ferromagnetic resonance was studied. Based on the ferromagnetic spectra, multiple spin wave modes were obtained in all films up to 120 nm. Spin wave modes along the lateral of the film originate from inhomogeneous confined magnetic regions on the film surface. Exchange stiffness constant of YIG films was estimated between 1.02×10⁻⁹ and 5.12 ×10⁻⁹ Oe.cm². We anticipate that these findings will bring up investment in advanced magnonics, insulator spintronics, and quantum information processing applications.
... On the other hand, the localized source of MW magnetic fields in a wide FM sam- ple and overall geometry of the PE experiment suggests non- locality of magnetization precession and the possibility for excitation of magnetostatic surface wave (MSSW). [57][58][59][60][61] In thin film geometry, the MSSW propagates with the wave vector ~ k aligned in-plane and perpendicular to the applied magnetic field, i.e., along the longest dimension of the FM sample in PE geometry. To capture the MSSW activity, we perform dynamic micromagnetic simulations employing a 2D 1 Â 1000 Â 12 mesh with 7 Â 0.05 Â 0.055 lm cells, fol- lowing Ref. 59. ...
In this work, we propose and explore a sensitive technique for investigation of ferromagnetic resonance and corresponding magnetic properties of individual micro-scaled and/or weak ferromagnetic samples. The technique is based on coupling the investigated sample to a high-Q transmission line superconducting resonator, where the response of the sample is studied at eigen frequencies of the resonator. The high quality factor of the resonator enables sensitive detection of weak absorption losses at multiple frequencies of the ferromagnetic resonance. Studying the microwave response of individual micro-scaled permalloy rectangles, we have confirmed the superiority of fluxometric demagnetizing factor over the commonly accepted magnetometric one and have depicted the demagnetization of the sample, as well as magnetostatic standing wave resonance.
... Another key requirement for logic implementation is non-reciprocity, ie., controlling the direction of signal flow such that the output gets affected by the input and not the reverse. Recently, the non-reciprocal behavior of magnetostatic surface spin waves has been investigated for logic applications 24,25 . The origin of the non-reciprocity was the interference of the spin waves produced by two different components (in-plane and out-of-plane) of the magnetic field due to a current flowing through the waveguide. ...
The possibility of using spin waves for information transmission and processing has been an area of active research due to the unique ability to manipulate the amplitude and phase of the spin waves for building complex logic circuits with less physical resources and low power consumption. Previous proposals on spin wave logic circuits have suggested the idea of utilizing the magneto-electric effect for spin wave amplification and amplitude- or phase-dependent switching of magneto-electric cells. Here, we propose a comprehensive scheme for building a clocked non-volatile spin wave device by introducing a charge-to-spin converter that translates information from electrical domain to spin domain, magneto-electric spin wave repeaters that operate in three different regimes - spin wave transmitter, non-volatile memory and spin wave detector, and a novel clocking scheme that ensures sequential transmission of information and non-reciprocity. The proposed device satisfies the five essential requirements for logic application: nonlinearity, amplification, concatenability, feedback prevention, and complete set of Boolean operations.
Here, we present a study investigating the effects of spin-wave coupling in a structure composed of parallel-oriented magnonic stripes fabricated from thin films of yttrium-iron garnet. The structure consists of two parallel stripes separated by a sufficiently small gap to enable dipolar coupling, while a third stripe is positioned atop the lateral system, forming an asymmetric three-dimensional (3D) coupler geometry. Through the utilization of Brillouin light-scattering spectroscopy, we experimentally demonstrate the transport of spin waves along the asymmetric 3D coupler. Additionally, by employing experimental techniques, we explore the nonreciprocal propagation of spin waves in the considered structure by reversing the polarity of the external magnetic field. To gain further insights, we employ micromagnetic modeling and the finite-element method to obtain the eigenmode spectra of the asymmetric 3D coupler. Our results show that reversing the polarity of the external magnetic field induces coupling between the magnetic stripes. We elucidate the characteristics of lateral and vertical spin-wave transport, as well as nonreciprocal spin-wave propagation within the investigated structure. Notably, in the asymmetric 3D coupler, the coupling length diminishes, offering the potential to enhance the density of functional elements in the design of three-dimensional magnonic networks.
In this work, magnetization dynamics is studied in superconductor-ferromagnet-superconductor three-layered films in a wide frequency, field, and temperature ranges using the broad-band ferromagnetic resonance measurement technique. It is shown that in the presence of both superconducting layers and of superconducting proximity at both superconductor-ferromagnet interfaces a massive shift of the ferromagnetic resonance to higher frequencies emerges. The phenomenon is robust and essentially long-range: it has been observed for a set of samples with the thickness of ferromagnetic layer in the range from tens up to hundreds of nanometers. The resonance frequency shift is characterized by proximity-induced magnetic anisotropies: by the positive in-plane uniaxial anisotropy and by the drop of magnetization. The shift and the corresponding uniaxial anisotropy grow with the thickness of the ferromagnetic layer. For instance, the anisotropy reaches 0.27 T in experiment for a sample with a 350-nm-thick ferromagnetic layer, and about 0.4 T in predictions, which makes it a ferromagnetic film structure with the highest anisotropy and the highest natural resonance frequency ever reported. Various scenarios for the superconductivity-induced magnetic anisotropy are discussed. As a result, the origin of the phenomenon remains unclear. Application of the proximity-induced anisotropies in superconducting magnonics is proposed as a way for manipulations with a spin-wave spectrum.
This work is focused on the numerical investigation of spin waves that propagate in nonlinear ferromagnet/superconductor bilayered films and periodic structures. The nonlinearity in these hybrid structures emerges due to the non-monotonous dependence of magnetization of a superconducting subsystem on the magnetic field, which is characterized by the superconducting critical field. It is shown that at relatively high amplitudes of spin waves in comparison to the superconducting critical field, the spin-wave spectrum changes drastically: the spin-wave spectral line can either bifurcate or stretch continuously depending on the type of considered superconductor. In addition, in the case of propagation of spin waves with relatively high amplitude in periodic magnonic metamaterials, additional zero-group-velocity modes appear that are known as flatbands. Overall, these findings suggest a versatile way for tunability of the spin-wave spectrum in nonlinear ferromagnet/superconductor structures by changing the excitation signal in respect to the superconducting critical field.
In this work, a class of metamaterials is proposed on the basis of ferromagnet/superconductor hybridization for applications in magnonics. These metamaterials comprise of a ferromagnetic magnon medium that is coupled inductively to a superconducting periodic microstructure. Spectroscopy of magnetization dynamics in such hybrid evidences formation of areas in the medium with alternating dispersions for spin wave propagation, which is the basic requirement for the development of metamaterials known as magnonic crystals. The spectrum allows for derivation of the impact of the superconducting structure on the dispersion: it takes place due to a diamagnetic response of superconductors on the external and stray magnetic fields. In addition, the spectrum displays a dependence on the superconducting critical state of the structure: the Meissner and the mixed states of a type II superconductor are distinguished. This dependence hints toward nonlinear response of hybrid metamaterials on the magnetic field. Investigation of the spin wave dispersion in hybrid metamaterials shows formation of allowed and forbidden bands for spin wave propagation. The band structures are governed by the geometry of spin wave propagation: in the backward volume geometry the band structure is conventional, while in the surface geometry the band structure is nonreciprocal and is formed by indirect band gaps. Placing a superconductor next to a ferromagnet makes it possible to modify the dispersion of spin waves. A ferromagnetic medium with a superconducting grid forms a magnonic crystal with allowed and forbidden frequency bands for spin wave propagation. The band structure of the crystal is shown to depend on the spin‐wave geometry as well as on the characteristics of superconducting microstructure.
Ferromagnetic resonance (FMR) in yttrium iron garnet (YIG)/Pt with a suitable YIG thickness in the submillimeter range show pure spin current contributions from the uniform FMR (UFMR) mode and various spin-wave resonance (SWR) modes, each with a different absorption intensity, inverse spin Hall voltage, and temperature dependence. The higher order mode of SWR with nonzero moment transferring along the thickness direction induces a maximum dc voltage among all modes. The spin current driven by UFMR and SWR has a linear T and power-law T dependence, respectively. In addition, the mixing conductance is derived for both modes, indicative of power-law T dependences. There is an absence of evidence for coherent spin pumping in YIG/Pt.
The dependence of nonreciprocity of excitation of magnetostatic surface waves on antenna width was investigated experimentally and theoretically. The nonreciprocity was successfully modified by changing the excitation antenna width. The nonreciprocity ratio, which was defined as the spin wave intensity under negative bias field divided by that under positive bias field, was found to decrease with increasing antenna width. Micromagnetic simulations revealed that this decrease in the nonreciprocity ratio originates from the rapid decrease in the in-plane excitation field compared to the perpendicular excitation field with reducing the antenna width.
In this work we consider dispersion laws of spin waves that propagate in a ferromagnet/superconductor bilayer, specifically, in a ferromagnetic film coupled inductively to a superconductor. The coupling is viewed as an interaction of a spin wave in ferromagnetic film with its mirrored image generated by the superconductor. We show that in general the coupling enhances substantially the phase velocity of magnons in in-plane spin wave geometries. In addition, a heavy nonreciprocity of the dispersion law is observed in the magnetostatic surface spin wave geometry where the phase velocity depends on the direction of the wave propagation.
In this work, a new hybridization of superconducting and ferromagnetic orders is demonstrated, promising for magnonics. By measuring the ferromagnetic and spin wave resonance absorption spectra of a magnetostatically coupled permalloy/niobium bilayer at different temperatures, magnetostatic spin wave resonances with unconventional dispersion are observed. The mechanism behind the modified dispersion, confirmed with micromagnetic simulations, implies screening of the alternating magnetostatic stray fields of precessing magnetic moments in the ferromagnetic layer by the superconducting surface in the Meissner state.
Ferromagnetic Heusler alloys with low magnetic damping are highly promising materials for magnonic devices, which rely on the excitation and detection of spin waves. Using all-electrical spin-wave spectroscopy we report spin-wave propagation in sputtered Co2(Mn0.6Fe0.4)Si Heusler alloy thin films with a thickness of 50 nm. We integrated a nanostructured microwave antenna to locally excite and detect propagating spin waves in a Damon-Eshbach configuration. We estimate the group velocity to be up to 12.0 km/s and we observe spin-wave propagation with a frequency band as broad as 15 GHz. From the experimental frequency dependence of group velocity we calculate the spin-wave dispersion. Our results show that all-electrical measurements are a powerful method for determining the fundamental spin-wave characteristics of Heusler alloys, over a broad and tunable range of frequencies, and with group velocities an order of magnitude higher than in conventional materials.
Excitation of non-reciprocal magnetostatic surface wave (MSSW) has been studied in an ultra-thin yttrium iron garnet (YIG) film. The YIG films were grown on a gadolinium gallium garnet (GGG) (111) substrate using pulsed laser deposition (PLD). The films exhibit an exceptional crystalline quality and an extremely low magnetic damping at radio frequency (RF) and microwave (MW). Non-reciprocal MSSWs in a 20.0 nm thick YIG film has been observed using a coupled coplanar waveguide (CCPW) structure with a shared common ground. Increase of the YIG film thickness to 190.0 nm, the nonreciprocity has been significantly enhanced, resulting in a maximum 10.0 dB amplitude gain and 55.5° phase shift in 30 mT magnetic field between the MSSWs traveling in opposite directions. In absence of magnetic field, the device shows a reduced amplitude gain of 2.0 dB and a phase shift of 15.8°. These results can find broad applications in building self-biased spin-wave based components in integrated signal processing and communication system.
We investigated the effect of the distance between a magnetic layer and an excitation antenna on the nonreciprocity of magnetostatic surface waves (MSSWs), using devices with various thicknesses of the SiO2 layer (t SiO2) to isolate an antenna from a permalloy layer. The nonreciprocity of MSSWs increases with increasing t SiO2. This increase in MSSW nonreciprocity is caused by an increase in the ratio of the MSSW excitation efficiency of the out-of-plane component of a microwave field to that of the in-plane component of a microwave field. Thus, we found that the nonreciprocity of MSSWs can be controlled by a very simple method.
The amplitude of the spin wave (magnetostatic surface spin wave) depends on the propagation direction. Nonreciprocity hardly depends on the permalloy (Py) thickness between 100 and 300 nm, and it is determined by the spin wave resonant frequency. The nonreciprocal parameter decreases with increasing frequency, resulting in the large amplitude asymmetry at high frequencies, which is well supported by a result of theoretical analysis. The nonreciprocity of a 25-nm-thick-film, however, is lower than those of thicker films. This is qualitatively explained by a schematic model based on the origin of nonreciprocity.
The effect of tantalum
(Ta) underlayer is investigated in Ni81Fe19
thin films for magnetization dynamics. The damping parameters extracted from spin wave measurements increase systematically with increasing Ta thickness, whereas the damping parameters from ferromagnetic resonance measurements are found to be weakly dependent on the Ta thickness. The difference is attributed to propagating properties of spin wave and short spin diffusion length in Ta. The group velocity of spin waves is found to be constant for different Ta thicknesses, and nonreciprocity of spin waves is not affected by the Ta thickness. The experimental observations are supported by micromagnetic simulations.
Spin-wave modes in Ni80Fe20 thin-film antidot lattices are investigated using micromagnetic simulations and a semianalytical theoretical approach. The simulations reveal a rich eigenmode spectrum consisting of edge and center modes. We find both spatially localized and spin waves extending over many unit cells. To classify the different types of modes and to analyze the microscopic properties, we adapt a semianalytical approach. We show how to reduce the two-dimensional problem of the antidot lattice to a one-dimensional problem if certain high-symmetry axes are considered. For lattices of unit-cell lengths ranging from 200 to 1100 nm, we find that the characteristic mode eigenfrequencies can be correlated with both local inhomogeneities of the demagnetization field and specific wave vectors caused by geometry-imposed mode quantization conditions. We compare our results with recently published experimental data and discuss the crossover from dipolar to exchange-dominated spin waves. Moreover, we simulate propagation of spin waves and find a preferred axis of propagation perpendicular to the external magnetic field.
We demonstrate the functionality of spin-wave logic exclusive-not-OR and not-AND gates based on a Mach-Zehnder-type interferometer which has arms implemented as sections of ferrite film spin-wave waveguides. Logical input signals are applied to the gates by varying either the phase or the amplitude of the spin waves in the interferometer arms. This phase or amplitude variation is produced by Oersted fields of dc current pulses through conductors placed on the surface of the magnetic films. (c) 2008 American Institute of Physics.
Early experiments in magnonics were made using ferrite samples, largely due to the intrinsically low magnetic (spin-wave) damping in these materials. Historically, magnonic phenomena were studied on micrometre to millimetre length scales. Today, the principal challenge in applied magnonics is to create sub-micrometre devices using modern polycrystalline magnetic alloys. However, until certain technical obstacles are overcome in these materials, ferrites—in particular yttrium iron garnet (YIG)—remain a valuable source of insight. At a time when interest in magnonic systems is particularly strong, it is both useful and timely to review the main scientific results of YIG magnonics of the last two decades, and to discuss the transferability of the concepts and ideas learned in ferrite materials to modern nano-scale systems.
The modulation of propagating spin-wave amplitude in Ni81Fe19 (Py) films,
resulting from constructive and destructive interference of spin wave, has been
demonstrated. Spin waves were excited and detected inductively using pulse
inductive time domain measurements. Two electrical impulses were used for
launching two interfering Gaussian spin wave packets in Py films. The applied
bias magnetic field or the separation between two pulses was used for tuning
the amplitude of the resulting spin wave packets. This may thus be useful for
spin wave based low-power information transfer and processing.
The authors have investigated the contribution of the surface spin waves to
spin pumping. A Pt/NiFe bilayer has been used for measuring spin waves and spin
pumping signals simultaneously. The theoretical framework of spin pumping
resulting from ferromagnetic resonance has been extended to incorporate spin
pumping due to spin waves. Equations for the effective area of spin pumping due
to spin waves have been derived. The amplitude of the spin pumping signal
resulting from travelling waves is shown to decrease more rapidly with
precession frequency than that resulting from standing waves and show good
agreement with the experimental data.
The authors have investigated the effect of the electrical pulse width of
input excitations on the generated spin waves in a NiFe strip using pulse
inductive time domain measurements. The authors have shown that the spin waves
resulting from the rising- and the falling-edges of input excitation pulses
interfere either constructively or destructively, and have provided conditions
for obtaining spin wave packets with maximum intensity at different bias
conditions.
We report ferromagnetic resonance experiments on Ga 1-x Mn x As thin films. For the dc magnetic field perpendicular to the sample plane, we observe up to eight distinct resonances, which we attribute to spin wave modes. To account for the spacing of the resonances, we infer a linear gradient in the magnetic properties, which is ascribed to a linear variation of the uniaxial magnetic anisotropy with film thickness. Values of D=(1±0.4)×10-9 Oe cm 2 for the spin stiffness and J MnMn ≈1 meV for the exchange integral between Mn spins are obtained. © 2003 American Institute of Physics.
We have studied experimentally the propagation of spin waves in microscopic transversally magnetized permalloy stripe waveguides with variable width. Spatially resolved measurement based on the microfocus Brillouin light-scattering spectroscopy allowed a direct observation of transformations of propagating transverse spin-wave modes in the region of the width transition. Our experiments show that due to the variation in the internal demagnetizing fields caused by the width variation, an effective control of the spin-wave propagation can be achieved. In particular, a splitting of a spin-wave beam into two independent beams or preferred excitation of certain transverse spin-wave modes can be realized.
We have studied experimentally the excitation of propagating spin-wave modes of a microscopic Permalloy-film waveguide by a stripe antenna. We show that due to the strong quantization of the spin-wave spectrum, the excitation of particular modes has essentially different frequency dependencies leading to a nonmonotonous variation of the modulation depth of the resulting spin-wave beam as a function of the excitation frequency. In addition, we address the effect of nonreciprocity of spin-wave excitation and found that for the case of Permalloy microwaveguides this effect is much weaker pronounced than for waveguides made from dielectric magnetic films with low saturation magnetization. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3231875]
We report on the linear response density functional study of the magnetization dynamics in Co(100) film driven by a nonuniform magnetic field. At resonant frequencies in the terahertz range, the magnetic field excites standing spin waves of the system and the induced magnetization penetrates the whole volume of the film. The pattern of magnetization precession is strongly influenced by the spin-flip excitations of single electrons which lead to the Landau damping of the spin-wave modes. Our results pave the way for the precise control of terahertz magnetization dynamics in itinerant magnets.
We propose a new protocol for implementing the two-qubit photonic phase gate. In our approach, the π phase is acquired by mapping two single photons into atomic excitations with fermionic character and exchanging their positions. The fermionic excitations are realized as spin waves in a spin chain, while photon storage techniques provide the interface between the photons and the spin waves. Possible imperfections and experimental systems suitable for implementing the gate are discussed.
Spin chains have long been considered as candidates for quantum channels to facilitate quantum communication. We consider the transfer of a single excitation along a spin-1/2 chain governed by Heisenberg-type interactions. We build on the work of Balachandran and Gong [1], and show that by applying optimal control to an external parabolic magnetic field, one can drastically increase the propagation rate by two orders of magnitude. In particular, we show that the theoretical maximum propagation rate can be reached, where the propagation of the excitation takes the form of a dispersed wave. We conclude that optimal control is not only a useful tool for experimental application, but also for theoretical enquiry into the physical limits and dynamics of many-body quantum systems. Comment: 10 pages, 15 figures
In electronics, information has been traditionally stored, processed and communicated using an electron's charge. This paradigm is increasingly turning out to be energy-inefficient, because movement of charge within an information processing device invariably causes current flow and an associated dissipation. Replacing 'charge' with the 'spin' of an electron to encode information may eliminate much of this dissipation and lead to more energy-efficient 'green electronics'. This realization has spurred significant research in spintronic devices and circuits where spin either directly acts as the physical variable for hosting information or augments the role of charge. In this review article, we discuss and elucidate some of these ideas, and highlight their strengths and weaknesses. Many of them can potentially reduce energy dissipation significantly, but unfortunately are error-prone and unreliable. Moreover, there are serious obstacles to their technological implementation that may be difficult to overcome in the near term.
This review addresses three constructs: (1) single devices or binary switches that can be constituents of Boolean logic gates for digital information processing, (2) complete gates that are capable of performing specific Boolean logic operations, and (3) combinational circuits or architectures (equivalent to many gates working in unison) that are capable of performing universal computation.
The spin torque effect that occurs in nanometre-scale magnetic multilayer devices can be used to generate steady-state microwave signals in response to a d.c. electrical current. This establishes a new functionality for magneto-electronic structures that are more commonly used as magnetic field sensors and magnetic memory elements. The microwave power emitted from a single spin torque nano-oscillator (STNO) is at present typically less than 1 nW. To achieve a more useful power level (on the order of microwatts), a device could consist of an array of phase coherent STNOs, in a manner analogous to arrays of Josephson junctions and larger semiconductor oscillators. Here we show that two STNOs in close proximity mutually phase-lock-that is, they synchronize, which is a general tendency of interacting nonlinear oscillator systems. The phase-locked state is distinct, characterized by a sudden narrowing of signal linewidth and an increase in power due to the coherence of the individual oscillators. Arrays of phase-locked STNOs could be used as nanometre-scale reference oscillators. Furthermore, phase control of array elements (phased array) could lead to nanometre-scale directional transmitters and receivers for wireless communications.
Experiments and simulations are reported, which demonstrate the influence of partial decoherence of spin-wave modes on the dynamics in small magnetic structures. Microfocus Brillouin light scattering spectroscopy was performed on 15 nm thick Ni81Fe19 rings with diameters from 1 to 3 microm. For the so-called "onion" magnetization state several effects were identified. First, in the pole regions of the rings spin-wave wells are created due to the inhomogeneous internal field leading to spin-wave confinement. Second, in the regions in between, modes are observed which show a well pronounced quantization in radial direction but a transition from partial to full coherency in azimuthal direction as a function of decreasing ring size. In particular for larger rings a continuous frequency variation with position is observed which is well reproduced by spin-wave calculations and micromagnetic simulations.
Using space-, time- and phase-resolved Brillouin light scattering spectroscopy we investigate the difference in phase of the two counterpropagating spin waves excited by the same microwave microstrip transducer. These studies are performed both for backward volume magnetostatic waves and magnetostatic surface waves in an in-plane magnetized yttrium iron garnet film. The experiments show that for the backward volume magnetostatic spin waves (which are reciprocal and excited symmetrically in amplitude) there is a phase difference of associated with the excitation process and thus the phase symmetry is distorted. On the contrary, for the magnetostatic surface spin waves (which are non-reciprocal and unsymmetrical in amplitude) the phase symmetry is preserved (there is no phase difference between the two waves associated with the excitation). Theoretical analysis confirms this effect.
It is demonstrated by SQUID measurements that (Ga,Mn)As films can exhibit perpendicular easy axis at low temperatures, even under compressive strain, provided that the hole concentration is sufficiently low. In such films, the easy axis assumes a standard in-plane orientation when the temperature is raised towards the Curie temperature or the hole concentration is increased by low temperature annealing. These findings are shown to corroborate quantitatively the predictions of the mean-field Zener model for ferromagnetic semiconductors. The in-plane anisotropy is also examined, and possible mechanisms accounting for its character and magnitude are discussed. Comment: 7 pages, 5 Postscript figures, uses revtex4
We study the effects of growth temperature, Ga:As ratio and post-growth annealing procedure on the Curie temperature, Tc, of (Ga,Mn)As layers grown by molecular beam epitaxy. We achieve the highest Tc values for growth temperatures very close to the 2D-3D phase boundary. The increase in Tc, due to the removal of interstitial Mn by post growth annealing, is counteracted by a second process which reduces Tc and which is more effective at higher annealing temperatures. Our results show that it is necessary to optimize the growth parameters and post growth annealing procedure to obtain the highest Tc.
It is fortunate that the garnet films that support magnetostatic wave propagation are also transparent to infrared light in the range of wavelengths between 1 and 5 μm. This includes wavelengths of 1.3 μm and 1.5 μm, which are of particular interest for optical fiber communications systems. Since a single film can be used simultaneously as a waveguide for optical and magnetostatic modes, interactions between these modes can be exploited for devices such as microwave spectrum analyzers, optical frequency shifters, tunable optical filters, and optical beam deflectors.
The characteristic modes of a thin slab magnetized in its plane are obtained in the magnetostatic limit,and the mode spectrum and configuration are discussed. The wavelength dependence of magnetostatic modedensity is determined and utilized to establish a connection to the modes obtained in the spin-wave approximation.In this geometry the modes lying above the spin-wave band are surface waves, decaying toward theinterior of the slab, while volume modes occur in the same frequency range as the long-wavelength limit ofthe spin-wave band of an infinite medium. The mode density exhibits poles at the upper and lower frequencylimits of the surface mode spectrum. The surface modes become statistically less important at shorter wavelengthsbecause the ratio of surface mode density to volume mode density varies approximately as 1/∣k∣.
This book is designed to give the student a fundamental, in-depth understanding of all the essential features of the magnetic recording process for both high density disk and tape recording. The book provides a thorough grounding in four basic areas of magnetic recording: structure and fields of heads and media, the replay process, the recording process, and medium noise analysis. Besides the fundamental issues, key systems questions of nonlinearities, overwrite, side track phenomena, error rate estimates as well as comparisons of MR and inductive heads will be discussed. The student will be able to use the information presented to design and analyze key experiments for head and medium evaluation as well as for overall system performance decisions. A parallel treatment of time and frequency response will enable the student to evaluate signal processing schemes. The book is intended either for senior-year undergraduates or first-year graduates. It assumes that the reader has had basic introductory electrical engineering or physics courses such as electricity and magnetism and applied mathematics.
This paper describes a systematic study of ferromagnetic resonance (FMR) carried out on a series of specimens of the ferromagnetic semiconductor Ga1-xMnxAs in thin film form. The GaMnAs layers were grown by low-temperature molecular beam epitaxy either on GaAs or on GaInAs buffers, the two buffers being used to obtain different strain conditions within the ferromagnetic layer. Our aim has been to map out the dependence of the FMR position on temperature and on the angle between the applied magnetic field and crystallographic axes of the sample. The analysis of the FMR data allowed us to obtain the values of the cubic and the uniaxial magnetic anisotropy fields---i.e., those which are associated with the natural (undistorted) zinc blende structure and those arising from of strain.
The authors have investigated the possibility of utilizing spin waves for
inter- and intra-chip communications, and as logic elements using both
simulations and experimental techniques. Through simulations it has been shown
that the decay lengths of magnetostatic spin waves are affected most by the
damping parameter, and least by the exchange stiffness constant. The damping
and dispersion properties of spin waves limit the attenuation length to several
tens of microns. Thus, we have ruled out the possibility of inter-chip
communications via spin waves. Experimental techniques for the extraction of
the dispersion relationship have also been demonstrated, along with
experimental demonstrations of spin wave interference for amplitude modulation.
The effectiveness of spin wave modulation through interference, along with the
capability of determining the spin wave dispersion relationships electrically
during manufacturing and testing phase of chip production may pave the way for
using spin waves in analog computing wherein the circuitry required for
performing similar functionality becomes prohibitive.
This review is devoted to both the experimental and theoretical aspects of lateral confinement effects observed for spin waves, with the wavevector in the 10 2-10 6 cm -1 range, where the magnetic dipole interaction plays the most important role. The Brillouin light scattering (BLS) technique is a powerful tool for the investigation of these effects. In addition to a high sensitivity, which is characteristic for a standard BLS system, we have extended the method to achieve high lateral spatial (30-50 mum), as well. As temporal (1-2 ns) resolution. This is central for the studies summarized in the review. Two representative experimental situations are reviewed: (1) Spin wave confinement in micron size laterally patterned structures (regular arrays of magnetic dots and wires). We focus on the quantization of spin wave wavevectors due to the lateral boundaries of a dot or a wire, and the influence of the static and dynamic coupling between islands. (2) Spatial, temporal and spatio-temporal confinement of linear and nonlinear spin waves in magnetic ferrite films. The formation, propagation, and collision of envelope solitons and their two-dimensional analogs (spin wave bullets) are analyzed. Both analytical and numerical models for spin waves in quasi-one-dimensional waveguides and in wide films are discussed
Gilbert damping for the epitaxial Co 2 FeAl Heusler alloy films was investigated. Gilbert damping constant for the films was evaluated by analyzing the data of ferromagnetic resonance measured at the frequency of 2–20 GHz. Gilbert damping constant for the film without annealing was rather large, while it decreased remarkably with postannealing. Gilbert damping constant for the film annealed at 600 ° C was ≃0.001 . These behavior of Gilbert damping constant can be well explained by the fact that the density of states calculated from first principles decreases with increasing the degree of B2 order.
GaAs-based diluted magnetic semiconductor, (Ga, Mn)As, with Mn composition x up to 0.07 was prepared by molecular-beam epitaxy on GaAs substrate at temperatures ranging from 160 to 320°C. Clear reflection high-energy electron diffraction oscillations were observed at the initial growth stage, indicating that the growth mode is two-dimensional. The lattice constant of (Ga, Mn)As films determined by X-ray diffraction showed a linear increase with the increase of Mn composition. Well-aligned in-plane ferromagnetic order was observed by magnetization measurements. Magnetotransport measurements also revealed the presence of ferromagnetic order in the (Ga, Mn)As layer. The easy axis of magnetization can be reversed by changing the strain direction in (Ga, Mn)As. superlattice structures with high crystal perfection and good interface quality were also prepared.
Novel material properties can be realized by designing waves' dispersion
relations in artificial crystals. The crystal's structural length scales may
range from nano- (light) up to centimeters (sound waves). Because of their
emergent properties these materials are called metamaterials. Different to
photonics, where the dielectric constant dominantly determines the index of
refraction, in a ferromagnet the spin-wave index of refraction can be
dramatically changed already by the magnetization direction. This allows a
different flexibility in realizing dynamic wave guides or spin-wave switches.
The present review will give an introduction into the novel functionalities of
spin-wave devices, concepts for spin-wave based computing and magnonic
crystals. The parameters of the magnetic metamaterials are adjusted to the
spin-wave k-vector such that the magnonic band structure is designed. However,
already the elementary building block of an antidot lattice, the singular hole,
owns a strongly varying internal potential determined by its magnetic dipole
field and a localization of spin-wave modes. Photo-magnonics reveal a way to
investigate the control over the interplay between localization and
delocalization of the spin-wave modes using femtosecond lasers, which is a
major focus of this review. We will discuss the crucial parameters to realize
free Bloch states and how, by contrast, a controlled localization might allow
to gradually turn on and manipulate spin-wave interactions in spin-wave based
devices in the future.
We report a time-resolved propagating spin wave spectroscopy for Fe19Ni81 film. We show that the amplitude of the spin-wave packet depends on the direction of magnetization and that its phase can be controlled by the polarity of pulsed magnetic field for the excitation. The nonreciprocal emission of spin-wave packet can be utilized for the binary spin-wave input into the spin-wave logic circuit.
The energy bandgap of an insulator is large enough to prevent electron excitation and electrical conduction. But in addition to charge, an electron also has spin, and the collective motion of spin can propagate-and so transfer a signal-in some insulators. This motion is called a spin wave and is usually excited using magnetic fields. Here we show that a spin wave in an insulator can be generated and detected using spin-Hall effects, which enable the direct conversion of an electric signal into a spin wave, and its subsequent transmission through (and recovery from) an insulator over macroscopic distances. First, we show evidence for the transfer of spin angular momentum between an insulator magnet Y(3)Fe(5)O(12) and a platinum film. This transfer allows direct conversion of an electric current in the platinum film to a spin wave in the Y(3)Fe(5)O(12) via spin-Hall effects. Second, making use of the transfer in a Pt/Y(3)Fe(5)O(12)/Pt system, we demonstrate that an electric current in one metal film induces voltage in the other, far distant, metal film. Specifically, the applied electric current is converted into spin angular momentum owing to the spin-Hall effect in the first platinum film; the angular momentum is then carried by a spin wave in the insulating Y(3)Fe(5)O(12) layer; at the distant platinum film, the spin angular momentum of the spin wave is converted back to an electric voltage. This effect can be switched on and off using a magnetic field. Weak spin damping in Y(3)Fe(5)O(12) is responsible for its transparency for the transmission of spin angular momentum. This hybrid electrical transmission method potentially offers a means of innovative signal delivery in electrical circuits and devices.
Ferromagnetism in manganese compound semiconductors not only opens prospects for tailoring magnetic and spin-related phenomena
in semiconductors with a precision specific to III-V compounds but also addresses a question about the origin of the magnetic
interactions that lead to a Curie temperature (T
C) as high as 110 K for a manganese concentration of just 5%. Zener's model of ferromagnetism, originally proposed for transition
metals in 1950, can explain T
C of Ga1−
xMnxAs and that of its II-VI counterpart Zn1−
xMnxTe and is used to predict materials with T
Cexceeding room temperature, an important step toward semiconductor electronics that use both charge and spin.
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