Showing papers on "Spin wave published in 1999"
IBM1
TL;DR: In this article, the excitation of spin waves in an unbounded ferromagnetic film by a direct spin-polarized current distributed over a small area is treated macroscopically.
541 citations
TL;DR: In this paper, the authors developed a theory of the extrinsic contributions to the ferromagnetic resonance linewidth and frequency shift of ultrathin films by two magnon scattering by defects at surfaces and interfaces.
Abstract: We develop a theory of the extrinsic contributions to the ferromagnetic resonance linewidth and frequency shift of ultrathin films. The basic mechanism is two magnon scattering by defects at surfaces and interfaces. In the presence of dipolar couplings between spins in the film, one realizes short wavelength spin waves degenerate with the ferromagnetic resonance (FMR) mode, provided the magnetization is parallel to the film surfaces. Defects on the surface or interface thus scatter the FMR mode into such short wavelength spin waves, producing a dephasing contribution to the linewidth, and a frequency shift of the resonance field. The mechanism described here is inoperative when the magnetization is perpendicular to the film.
478 citations
TL;DR: Different ways to define and calculate the degree of spin polarization in a ferromagnet are discussed, particularly with respect to spin-polarized tunneling and Andreev reflection at the boundary between superconductor and ferromagnetic as mentioned in this paper.
Abstract: Different ways to define and calculate the degree of spin polarization in a ferromagnet are discussed, particularly with respect to spin-polarized tunneling and Andreev reflection at the boundary between superconductor and ferromagnet. As an example, the degree of spin polarization for different experiments in Fe and Ni is calculated in the framework of the local spin density approximation and used to illustrate the differences between various definitions of spin polarization.
358 citations
TL;DR: In this paper, the authors proposed a spin-interference device which works even without any ferromagnetic electrodes and any external magnetic field, which can be expected in the AB ring with a uniform spin-orbit interaction, which causes the phase difference between the spin wave functions traveling in the clockwise and anticlockwise direction.
Abstract: We propose a spin-interference device which works even without any ferromagnetic electrodes and any external magnetic field. The interference can be expected in the Aharonov–Bohm (AB) ring with a uniform spin-orbit interaction, which causes the phase difference between the spin wave functions traveling in the clockwise and anticlockwise direction. The gate electrode, which covers the whole area of the AB ring, can control the spin-orbit interaction, and therefore, the interference. A large conductance modulation effect can be expected due to the spin interference.
289 citations
TL;DR: By driving with a microwave pulse the lowest frequency antiferromagnetic resonance of the quasi-1D biaxial antifromagnet into an unstable region, intrinsic localized spin waves have been generated and detected in the spin wave gap as discussed by the authors.
Abstract: By driving with a microwave pulse the lowest frequency antiferromagnetic resonance of the quasi-1D biaxial antiferromagnet $({\mathrm{C}}_{2}{\mathrm{H}}_{5}{\mathrm{NH}}_{3}{)}_{2}{\mathrm{CuCl}}_{4}$ into an unstable region, intrinsic localized spin waves have been generated and detected in the spin wave gap. These findings are consistent with the prediction that nonlinearity plus lattice discreteness can lead to localized excitations with dimensions comparable to the lattice constant.
202 citations
TL;DR: An electrodynamic theory of GMI, based on a simultaneous solution of linearized Maxwell's equations and Landau-Lifshitz equation of motion, is presented in this paper.
202 citations
TL;DR: In this article, a review of the current understanding of the spin relaxation of conduction electrons in nonmagnetic semiconductors and metals is presented in the perspective of current understanding.
Abstract: Prospect of building electronic devices in which electron spins store and transport information has revived interest in the spin relaxation of conduction electrons. Since spin-polarized currents cannot flow indefinitely, basic spin-electronic devices must be smaller than the distance electrons diffuse without losing its spin memory. Some recent experimental and theoretical effort has been devoted to the issue of modulating the spin relaxation. It has been shown, for example, that in certain materials doping, alloying, or changing dimensionality can reduce or enhance the spin relaxation by several orders of magnitude. This brief review presents these efforts in the perspective of the current understanding of the spin relaxation of conduction electrons in nonmagnetic semiconductors and metals.
161 citations
TL;DR: An experimental study of spin-wave quantization in arrays of micron-size magnetic wires by means of Brillouin light-scattering spectroscopy is reported in this paper, where Dipolar-dominated Damon-Eshbach spinwave modes laterally quantized in a single wire with quantized wave vector values determined by the width of the wire are studied.
Abstract: An experimental study of spin-wave quantization in arrays of micron-size magnetic ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ wires by means of Brillouin light-scattering spectroscopy is reported Dipolar-dominated Damon-Eshbach spin-wave modes laterally quantized in a single wire with quantized wave vector values determined by the width of the wire are studied The frequency splitting between quantized modes, which decreases with increasing mode number, depends on the wire sizes and is up to 15 GHz The transferred wave vector interval, where each mode is observed, is calculated using a light-scattering theory for confined geometries The frequencies of the modes are calculated, taking into account finite-size effects The results of the calculations are in a good agreement with the experimental data
157 citations
TL;DR: In this paper, the spin-dependent transport in a ferromagnetic/superconductor/ferromagnet double tunnel junction was theoretically studied and the results provided a new method not only for measuring the spin polarization of ferromagnets but also for controlling superconductivity and tunnel magnetoresistance by applying a bias voltage.
Abstract: We theoretically study the spin-dependent transport in a ferromagnet/superconductor/ferromagnet double tunnel junction. The tunneling current in the antiferromagnetic alignment of the magnetizations gives rise to a spin imbalance in the superconductor. The resulting nonequilibrium spin density strongly suppresses the superconductivity with increase of bias voltage and destroys it at a critical voltage ${V}_{c}$. The results provide a new method not only for measuring the spin polarization of ferromagnets but also for controlling superconductivity and tunnel magnetoresistance by applying a bias voltage.
149 citations
TL;DR: In this paper, the nonlinear spin dynamics of an anisotropic Heisenberg ferromagnetic spin chain with octupole-dipole interaction in the semiclassical limit using the coherent-state method combined with the Holstein-Primakoff bosonic representation of spin operators were investigated.
Abstract: We investigate the nonlinear spin dynamics of an anisotropic Heisenberg ferromagnetic spin chain with octupole-dipole interaction in the semiclassical limit using the coherent-state method combined with the Holstein-Primakoff bosonic representation of spin operators. The dynamics is found to be governed by a generalized nonlinear Schr\"odinger equation in the continuum limit. For specific values of the exchange, octupole-dipole interactions, and also of the anisotropy parameters, through Painlev\'e singularity structure analysis, we have identified an integrable spin chain model with soliton spin excitations. We carry out a multiple scale perturbation analysis to find the discreteness effect on the soliton excitations in the more general nonintegrable case.
111 citations
TL;DR: In this paper, a cluster variational theory, within pair approximation, of the mixed spin 1 2 -spin 1 ferrimagnet with single-ion anisotropy, is presented.
TL;DR: Using the adiabatic approximation, this paper derived the equations of motion for local spin moments which are valid for itinerant as well as tight-binding spins, and obtained the material parameters in the equation of motion using standard density functional methods, which depend only on the energy and Berry phase of the constrained ground state of frozen spin configurations.
Abstract: Using the adiabatic approximation, we derive the equations of motion for local spin moments which are valid for itinerant as well as tight-binding spins. Material parameters in the equations of motion can be obtained using standard density functional methods, because they depend only on the energy and Berry phase of the constrained ground state of frozen spin configurations. For the calculation of spin waves in a collinear magnet, it is sufficient to know the quadratic forms of total energy and spin component along the symmetry axis as functions of the spin deviations from the ground state configuration. {copyright} {ital 1999} {ital The American Physical Society}
TL;DR: In this paper, the authors present theoretical studies based on the use of realistic electronic structures, which conclude that in the spin polarized electron energy loss spectrum of Fe and of ultrathin Fe films a strong signature of spin waves should appear for energy losses in the range of 250 meV and below.
Abstract: We present theoretical studies based on the use of realistic electronic structures, which conclude that in the spin polarized electron energy loss spectrum of Fe and of ultrathin Fe films a strong signature of spin waves should appear for energy losses in the range of 250 meV and below. New experimental data we present show that indeed the spin asymmetry in the loss spectrum increases dramatically in this regime, as expected from its presence.
TL;DR: In this article, the spin pairing energy in high-temperature superconductivity in copper oxides has been investigated and it has been shown that the spin gap energy is wavevector independent.
Abstract: A notable aspect of high-temperature superconductivity in the copper oxides is the unconventional nature of the underlying paired-electron state. A direct manifestation of the unconventional state is a pairing energy—that is, the energy required to remove one electron from the superconductor—that varies (between zero and a maximum value) as a function of momentum, or wavevector1,2: the pairing energy for conventional superconductors is wavevector-independent3,4. The wavefunction describing the superconducting state will include the pairing not only of charges, but also of the spins of the paired charges. Each pair is usually in the form of a spin singlet5, so there will also be a pairing energy associated with transforming the spin singlet into the higher-energy spin triplet form without necessarily unbinding the charges. Here we use inelastic neutron scattering to determine thewavevector-dependence of spin pairing in La2−xSrxCuO4, the simplest high-temperature superconductor. We find that the spin pairing energy (or ‘spin gap’) is wavevector independent, even though superconductivity significantly alters the wavevector dependence of the spin fluctuations at higher energies.
TL;DR: In this article, the transport and magnetic properties of a series of NiBC compounds were studied for a large range of temperatures (T) and magnetic fields (H) and it was shown that below the critical temperature, the temperature dependence of the resistivity is determined by electron scattering due to the spin waves of the ordered magnetic phase and the values of the gap in the magnon spectra were derived.
Abstract: We present a study of the transport and magnetic properties of a series of $R\mathrm{NiBC}$ compounds $(R=\mathrm{Er},$ Ho, Dy, Tb, and Gd). All the materials investigated have long range magnetic order at sufficiently low temperatures. Magnetoresistance measurements are presented for a large range of temperatures (T) and magnetic fields (H). We show that below the critical temperature, the temperature dependence of the resistivity is determined by electron scattering due to the elementary excitations (spin waves) of the ordered magnetic phase and the values of the gap in the magnon spectra were derived. Finally we discuss the $H\ifmmode\times\else\texttimes\fi{}T$ phase diagram of these materials.
TL;DR: In this article, the authors analyzed the self-consistent spin-wave theories of two-dimensional Heisenberg ferro-and antiferromagnets with a weak interlayer coupling and/or magnetic anisotropy, based on the nonlinear Dyson-Maleev, Schwinger, and combined boson-pseudofermion representations.
Abstract: The versions of the self-consistent spin-wave theories (SSWT) of two-dimensional Heisenberg ferro- and antiferromagnets with a weak interlayer coupling and/or magnetic anisotropy, that are based on the nonlinear Dyson-Maleev, Schwinger, and combined boson-pseudofermion representations, are analyzed. Analytical results for the temperature dependences of (sublattice) magnetization and the short-range order parameter, and the critical points are obtained. The influence of external magnetic field is considered. Fluctuation corrections to SSWT are calculated within a random-phase approximation which takes into account correctly leading and next-leading logarithmic singularities. These corrections are demonstrated to improve radically the agreement with experimental data on layered perovskites and other systems. Thus an account of these fluctuations provides a quantitative theory of layered magnets.
TL;DR: For non-collinear magnetic alignment is somewhat unusual for equilibrium, and those systems exhibiting such ground states are frequently 'victims' of competing forces as discussed by the authors, however, magnetic alignment for non-equilibrium, or dynamical systems is universal.
TL;DR: In this paper, the ground state and low-lying excitations of the S = 1/2 alternating Heisenberg antiferromagnetic chain were determined using numerical diagonalization.
Abstract: In this paper we present results for the ground state and low-lying excitations of the S=1/2 alternating Heisenberg antiferromagnetic chain. Our more conventional techniques include perturbation theory about the dimer limit and numerical diagonalization of systems of up to 28 spins. An application of multiple precision numerical diagonalization allows us to determine analytical perturbation series to high order; the results found using this approach include ninth-order perturbation series for the ground state energy and one magnon gap. We also determine the fifth-order dispersion relation and third-order exclusive neutron scattering structure factor for one-magnon modes and numerical and analytical binding energies of S=0 and S=1 two-magnon bound states. {copyright} {ital 1999} {ital The American Physical Society}
TL;DR: In this article, the modulational instability of extended nonlinear spin waves is discussed as a mechanism for dynamical localization of spin waves in homogeneous magnetic lattices, and both static and dynamic properties of intrinsic localized spin wave gap modes and resonant modes are surveyed in detail.
TL;DR: In this article, the generalized Holstein-Primakoff transformation is used to develop a quantum flavor wave theory for spin systems with orbital degeneracy, which gives rise to quantum fluctuations of reduced dimensionality.
Abstract: The generalized Holstein-Primakoff transformation is used to develop a quantum flavor wave theory for spin systems with orbital degeneracy. Elementary excitations of ordered ground states consist of spin, orbital, and spin-orbital waves. Spin and spin-orbital waves couple to each other due to orbital anisotropy and Hund's rule, resulting in modes observable by inelastic neutron scattering. In the $\mathrm{SU}(4)$ limit, flavor waves are dispersionless along one or more directions, and give rise to quantum fluctuations of reduced dimensionality.
TL;DR: In this article, the Brillouin light-scattering spectroscopy was used for spin-wave quantization in square arrays of micron-size circular magnetic Ni80Fe20 dots.
Abstract: We report on the observation of spin-wave quantization in square arrays of micron-size circular magnetic Ni80Fe20 dots by means of Brillouin light-scattering spectroscopy. For a large wave-vector interval several discrete, dispersionless modes with a frequency splitting of up to 2.5 GHz were observed. The modes are identified as magnetostatic surface spin waves laterally quantized due to in-plane confinement in each single dot. The frequencies of the lowest observed modes decrease with increasing distance between the dots, thus indicating an essential dynamic magnetic dipole interaction between the dots at small interdot distances.
TL;DR: In this article, the effects of spontaneous symmetry breaking from a unified point of view are investigated in nonrelativistic systems exhibiting collective magnetic behavior in the framework of effective Lagrangians, and analogies between condensed matter physics and Lorentz-invariant theories are pointed out.
Abstract: Nonrelativistic systems exhibiting collective magnetic behavior are analyzed in the framework of effective Lagrangians. The method, formulating the dynamics in terms of Goldstone bosons, allows us to investigate the consequences of spontaneous symmetry breaking from a unified point of view. Low-energy theorems concerning spin-wave scattering in ferromagnets and antiferromagnets are established, emphasizing the simplicity of actual calculations. The present work includes approximate symmetries and discusses the modification of the low-energy structure imposed by an external magnetic and an anisotropy field, respectively. Throughout the paper, analogies between condensed matter physics and Lorentz-invariant theories are pointed out, demonstrating the universal feature of the effective Lagrangian technique.
TL;DR: In this paper, the Schwinger-boson mean field theory is applied to the quantum ferrimagnetic Heisenberg chain and the thermodynamic observables, such as the free energy, magnetic susceptibility, specific heat, and the spin correlation at T>0 K, are calculated.
Abstract: The Schwinger-boson mean-field theory is applied to the quantum ferrimagnetic Heisenberg chain. There is a ferrimagnetic long-range order in the ground state. We observe two branches of the low-lying excitation and calculate the spin reduction, the gap of the antiferromagnetic branch, and the spin fluctuation at T=0 K. These results agree with the established numerical results quite well. At finite temperatures, the long-range order is destroyed because of the disappearance of the Bose condensation. The thermodynamic observables, such as the free energy, magnetic susceptibility, specific heat, and the spin correlation at T>0 K, are calculated. The T chi(uni) has a minimum at intermediate temperatures and the spin-correlation length behaves as T-1 at low temperatures. These qualitatively agree with the numerical results and the difference is small at low temperatures. [S0163-1829(99)07225-2].
TL;DR: In this paper, the effect of quantum spin fluctuations on the ground-state properties of the Heisenberg antiferromagnet on an anisotropic triangular lattice using linear spin-wave (LSW) theory was investigated.
Abstract: We consider the effect of quantum spin fluctuations on the ground-state properties of the Heisenberg antiferromagnet on an anisotropic triangular lattice using linear spin-wave (LSW) theory. This model should describe the magnetic properties of the insulating phase of the family of superconducting molecular crystals. The ground-state energy, the staggered magnetization, magnon excitation spectra, and spin-wave velocities are computed as functions of the ratio of the antiferromagnetic exchange between the second and first neighbours, . We find that near , i.e., in the region where the classical spin configuration changes from a Neel-ordered phase to a spiral phase, the staggered magnetization vanishes, suggesting the possibility of a quantum disordered state. In this region, the quantum correction to the magnetization is large but finite. This is in contrast to the case for the frustrated Heisenberg model on a square lattice, for which the quantum correction diverges logarithmically at the transition from the Neel to the collinear phase. For large , the model becomes a set of chains with frustrated interchain coupling. For , the quantum correction to the magnetization, within LSW theory, becomes comparable to the classical magnetization, suggesting the possibility of a quantum disordered state. We show that, in this regime, the quantum fluctuations are much larger than for a set of weakly coupled chains with non-frustrated interchain coupling.
TL;DR: In this paper, an experimental and theoretical study of the normal magnetic modes in spiral ferromagnetic structures is presented, which results in a structure similar to that encountered in a Bloch domain wall.
Abstract: An experimental and theoretical study is presented of the normal magnetic modes in spiral ferromagnetic structures. The bilayer system studied consists of Fe layers (25, 50, 100, and 200 A thick) that are exchange coupled to 200 A thick SmCo films that have ≈200 kOe anisotropies. The Fe spiral—induced by an external magnetic field that is applied opposite to the direction of the magnetized film—results in a structure similar to that encountered in a Bloch domain wall. The magnetization and the field dependence of the magnons in various Fe films are explained by the theoretical model.
TL;DR: In this article, the reorientation of the magnetization of a ferromagnetic monolayer is calculated with the help of many-body Green's function theory, which allows, in contrast to other spin wave theories, a satisfactory calculation of magnetic properties over the entire temperature range of interest since interactions between spin waves are taken into account.
Abstract: The reorientation of the magnetization of a ferromagnetic monolayer is calculated with the help of many-body Green's function theory. This allows, in contrast to other spin wave theories, a satisfactory calculation of magnetic properties over the entire temperature range of interest since interactions between spin waves are taken into account. A Heisenberg Hamiltonian plus a second-order uniaxial single-ion anisotropy and an external magnetic field is treated by the Tyablikov (Random Phase Approximation: RPA) decoupling of the exchange interaction term and the Anderson-Callen decoupling of the anisotropy term. The orientation of the magnetization is determined by the spin components $\la S^\alpha\ra$ ($\alpha=x,y,z$), which are calculated with the help of the spectral theorem. The knowledge of the orientation angle $\Theta_0$ allows a non-perturbative determination of the temperature dependence of the effective second-order anisotropy coefficient. Results for the Green's function theory are compared with those obtained with mean-field theory (MFT). We find significant differences between these approaches.
TL;DR: In this article, measurements of the magnetization and electrical resistivity of TmB 12, ErB 12, HoB 12 and DyB 12 polycrystalline samples were taken in the paramagnetic state as well as in the magnetically ordered regime.
TL;DR: In this article, a single crystal of Fe{sub 0.7}Al was investigated over a wide range of energy and reciprocal space with inelastic neutron scattering, and the spin dynamics were strongly q dependent, suggesting remnant short-range spin correlations.
Abstract: Spin excitations in a single crystal of Fe{sub 0.7}Al {sub 0.3} were investigated over a wide range of energy and reciprocal space with inelastic neutron scattering. In the ferromagnetic phase, propagating spin wave modes become paramagnonlike diffusive modes beyond a critical wave vector {bold q}{sub 0} , indicating substantial disorder in the long-range ordered state. In the spin glass phase, the spin dynamics are strongly q dependent, suggesting remnant short-range spin correlations. {copyright} {ital 1999} {ital The American Physical Society}
TL;DR: In this article, a solution for the general problem of the nonstationary interaction of backward volume magnetostatic waves in films of yttrium-iron garnet with local parametric pumping is obtained.
Abstract: A solution is obtained for the general problem of the nonstationary interaction of backward volume magnetostatic waves in films of yttrium-iron garnet with local parametric pumping. In the case of a large pump region, l≫λ, where λ is the wavelength of the backward volume magnetostatic waves, the problem reduces to a system of truncated equations for two packets of counter propagating waves. In the opposite case, l<λ, the exact problem of parametric interactions of the eigenmodes of a ferrite film (both counterpropagating and in the same direction) is solved numerically. Both cases are studied experimentally and good qualitative and quantitative agreement is obtained with the theory. For the first time, the reversal of a wave front and the time reversal of the shape of backward volume magnetostatic wave pulses are observed and a change in the propagation time for the peak of the signal pulse and a reduction in its width owing to pumping are recorded. Two operating regimes are identified for a nonstationary parametric backward volume magnetostatic wave amplifier with local pumping, which differ in the ratio of the duration of the pump pulse to the transit time for the wave through the local pump region, and the effect of the parametric excitation of two-dimensional spin waves on the interaction of backward volume magnetostatic waves with a local nonstationary parametric pump is determined.
TL;DR: In this paper, a formalism for calculating ab initio spin-wave spectra based on the many-body temperature Green's function is proposed, which avoids both the assumption of local spins (Heisenberg model) and the use of a local exchange and correlation interaction (local-density approximation).
Abstract: We propose a formalism for calculating ab initio spin-wave spectra which is based on the many-body temperature Green's function. The main quantity to be calculated is the linear magnetic susceptibility from which all magnetic excitations involving the creation of an additional spin in the system can formally be obtained. The Schwinger functional derivative technique is employed in calculating the self-energy. The approach avoids both the assumption of local spins (Heisenberg model) and the use of a local exchange and correlation interaction (local-density approximation). Starting from the GW approximation we obtain a Bethe-Salpeter equation for the kernel describing the interaction between electrons in both spin channels. However, this kernel exhibits a nonlocal screened interaction.