Showing papers on "Spin wave published in 1984"
TL;DR: The theory of spin exchange between optically pumped alkali-inetal atoms and noble-gas nuclei is presented in this article, where the main spin interactions are assumed to be the spin-rotation interactions yN S between the rotational angular momentum N of the alkali ion and the electron spin S of the noble ion.
Abstract: The theory of spin exchange between optically pumped alkali-Inetal atoms and noble-gas nuclei is presented. Spin exchange with heavy noble gases is dominated by interactions in long-lived van der Waals molecules. The main spin interactions are assumed to be the spin-rotation interactions yN S between the rotational angular momentum N of the alkali-metal — noble-gas pair and the electron spin S of the alkali-metal atom, and the contact hyperfine interaction aK S between the nuclear spin K of the noble-gas atom and the electron spin S. Arbitrary values for EC and for the nuclear spin I of the alkali-metal atom are assumed. Precise formal expressions for spin transfer coefficients are given along with convenient approximations based on a perturbation expansion in powers of (o.'/yX), a quantity which has been shown to be small by experiment.
404 citations
TL;DR: In this paper, a consistent and uniform exposition of all known results related to the Heisenberg model is given and the classification of excitations is presented and their scattering is described both in ferromagnetic and antiferromagnetic cases.
Abstract: The work gives a consistent and uniform exposition of all known results related to Heisenberg model. The classification of excitations is presented and their scattering is described both in ferromagnetic and the antiferromagnetic cases. It is shown that in the antiferromagnetic case there exists only one excitation with spin 1/2 which is a kink in the following sense: in physical states there is only an even number of kinks-spin waves, therefore they always have an integer spin. Thus, it is shown that the conventional picture of excitations Is wrong in the antiferromagnetic case and the spin wave has spin 1/2, matrix is calculated.
300 citations
TL;DR: In this paper, the results for the exchange parameters and the spin-wave stiffness constant of ferromagnetic metals were obtained using a local spin-density functional formalism and the muffin-tin potential model.
Abstract: Rigorous expressions for the exchange parameters and the spin-wave stiffness constant of ferromagnetic metals are obtained using a local spin-density functional formalism and the muffin-tin potential model. The calculated results for ferromagnetic iron are given as an example of the approach.
233 citations
TL;DR: In this article, a review of low to moderate frequency magnetic excitations, termed magnons or spin waves, in magnetically ordered materials is presented, focusing on intuitive behavior rather than analytical theory.
94 citations
TL;DR: In this article, Ferromagnetic resonance in a polished 0.047-cm-radius sphere of gallium-doped yttrium iron garnet is studied at 1.3 GHz in a magnetic field of 460 G.
Abstract: Ferromagnetic resonance in a polished 0.047-cm-radius sphere of gallium-doped yttrium iron garnet is studied at 1.3 GHz in a magnetic field of 460 G. A second-order Suhl instability is observed, owing to the nonlinear coupling of the precessing uniform magnetization with spin waves. This is detected by the onset of auto-oscillations of the magnetization. One of these modes with frequency \ensuremath{\approx}16 kHz corresponds to the lowest spherical dimensional resonance of a packet of spin waves of small wave vector and long lifetime (\ensuremath{\approx} ${10}^{3}$ cycles). From real-time signals, spectral analysis, and return maps this mode is found to display chaotic dynamics as the driving rf field is increased: thresholds for the onset of period-doubling bifurcations, chaos, and periodic windows. Some observed return maps bear resemblance to the two-dimensional area-preserving quadratic map of H\'enon. The system has several attractors and displays "solid-state turbulence," analogous to that in fluids.
94 citations
TL;DR: In this paper, the authors observed narrow resonances in the NMR spectrum of dilute spinpolarized atomic hydrogen gas and measured the parameters of exchange effects in spin-transport processes.
Abstract: We have observed narrow, distinct resonances in the NMR spectrum of dilute spinpolarized atomic hydrogen gas ($n\ensuremath{\sim}{10}^{16}$ atoms/${\mathrm{cm}}^{3}$). The dependence of the observed spectra on temperature, density, polarization, and magnetic field gradient is consistent with theoretical predictions for spin-wave excitations damped by diffusion. We have measured the parameter $\ensuremath{\mu}$, which is a measure of the importance of exchange effects in spin-transport processes, and the diffusion coefficient ${D}_{0}$, both of which are in reasonable agreement with theory.
93 citations
TL;DR: In this paper, it was shown that the effect of the Landau-Lifshitz-Gilbert damping term is a mere rescaling of time by a complex constant.
Abstract: In the Landau-Lifshitz equation which describes the evolution of spin fields in nonequilibrium continuum ferromagnets, by stereographic projection of the unit sphere of spin onto a complex plane, it is shown that the effect of the Landau-Lifshitz-Gilbert damping term is a mere rescaling of time by a complex constant. Consequently, for any given undamped motion of spatially regular and/or irregular spin structures, the nature of the damping can be analyzed exactly in a simplified manner.
88 citations
TL;DR: In this article, the ground state energy and spin wave modes for an anisotropic Heisenberg chain of arbitrary spin were obtained for the Ising-like anisotropy, while for the XY -like case there was no gap.
81 citations
TL;DR: In this paper, the authors applied low-order spin-wave analysis to the antiferromagnetic plane rotator model on the triangular lattice in order to study the low-temperature properties in the presence of magnetic fields.
Abstract: Lowest-order spin-wave analysis is applied to the antiferromagnetic plane rotator model on the triangular lattice in order to study the low-temperature properties in the presence of magnetic fields. Equilibrium spin configuration in the zero-temperature limit is calculated as a function of the magnetic field. It is found that the thermal-fluctuation effect reduces a continuous degeneracy of the ground state to a discrete one at non-zero temperatures.
69 citations
TL;DR: In this article, the authors measured the spin wave spectrum of iron by neutron inelastic scattering using the Low-Resolution Medium-Energy Chopper Spectrometer at the Intense Pulsed Neutron Source (IPNS) of the Argonne National Laboratory.
Abstract: We have measured the spin‐wave spectrum of iron by neutron inelastic scattering using the Low‐Resolution Medium‐Energy Chopper Spectrometer at the Intense Pulsed Neutron Source (IPNS) of the Argonne National Laboratory. Interest focuses on the magnetic excitations at high energy transfers where the spin‐wave dispersion relation has not previously been determined. In measurements performed at 10 K using a 23‐g single crystal of pure iron, we observed magnetic scattering around the (110) reciprocal lattice point with spin‐wave energies from 40 to 160 meV. The spin waves over the entire range of energy are found to be consistent with an isotropic spin‐wave dispersion relation. With the present experimental sensitivity we were unable to observe any band structure effects such as Stoner excitations or optical magnons in this range of wave vector and energy.
66 citations
TL;DR: In this paper, the role of surface anisotropy energies in determining the boundary conditions of standing spin wave modes in thin films is developed in some detail in this model, which is subsquently introduced and shown to be equivalent to the microscopic model.
TL;DR: In this article, the authors performed a study of magnons in Mo/Ni metallic superlattices with the use of Brillouin scattering and found that the magnetic field and modulation wavelength dependence of the magnon frequencies were in reasonable agreement with theoretical predictions.
Abstract: We have performed a study of magnons in Mo/Ni metallic superlattices with the use of Brillouin scattering. The magnetic field and modulation wavelength dependence of the magnon frequencies are found to be in reasonable agreement with theoretical predictions. Certain features in the spectra which are characteristic of a superlattice and cannot be expalined by a trivial superposition of the spectra of the individual constituent layers are presented and discussed.
TL;DR: In this paper, the character of magnetostatic waves is calculated for such systems and is illustrated for three different layers variously spaced (accurate control of the delay characteristics is shown to be possible) as well as for very many similar layers equally spaced.
Abstract: Collective magnetic excitations are supported by multiple ferrite layers. The character of magnetostatic waves is calculated for such systems and is illustrated for three different layers variously spaced (accurate control of the delay characteristics is shown to be possible) as well as for very many similar layers equally spaced. For volume waves on many layers, collective spin-wave-like modes of long wavelength form a continuum that evolves smoothly into narrow bands characteristic of the layers at short wavelength. For surface waves, an excitation similar to the surface wave on a continuous medium appears when the spacing is less than the layer thickness, but a dense continuum of other excitations (not analogous to those of a uniform medium) always persists even for small spacings. This unexpected spectrum is related to a novel system of modes localized on the gaps.
TL;DR: In this article, the spin dynamics of weakly interacting, spin-polarized quantum gases are discussed in terms of a quasiparticle picture of these systems, and the theory is used to discuss magnetic resonance experiments in spin polarized atomic hydrogen.
Abstract: The spin dynamics of weakly interacting, spin-polarized quantum gases are discussed in terms of a quasiparticle picture of these systems. Quantum mechanical exchange between identical particles introduces "molecular" magnetic fields which give rise to the precession of the spin current; this in turn leads to coherent oscillations of the magnetization. The theory is used to discuss magnetic resonance experiments in spin-polarized atomic hydrogen.
TL;DR: In this article, the identical spin rotation effect was observed in 3He↑ in the temperature range 2 < T < 6 K, and preliminary measurements of the coefficient μ which characterizes the quality factor of the spin oscillations were made.
Abstract: Spin polarized gases such as H↑ or 3He↑ can propagate damped spin waves at low temperatures; their origin is the so-called « identical spin rotation effect » in collisions between identical particles. We report here the observation of such effects in 3He↑ in the temperature range 2 < T < 6 K, and preliminary measurements of the coefficient μ which characterizes the quality factor of the spin oscillations. The measurements are in agreement with the numerical calculations of C. Lhuillier.
TL;DR: Inelastic neutron scattering measurements have been performed on a Ni0.784Mn0.216 disordered alloy which is ferromagnetic below 330K as discussed by the authors, and the inelastic scattering reveals a marked anomaly of the spin dynamics at about 100k below which a quasi-elastic line appears and grows in intensity as commonly observed in similar reentrant systems.
Abstract: Inelastic neutron scattering measurements have been performed on a Ni0.784Mn0.216 disordered alloy which is ferromagnetic below 330K. At temperatures lower than 40K the AC susceptibility measurements suggest the onset of a frustrated phase. Spin waves have been unambiguously observed at all temperatures below the Curie temperature 330K, and in particular below 40K. The inelastic scattering reveals a marked anomaly of the spin dynamics at about 100K below which a quasi-elastic line appears and grows in intensity as commonly observed in similar re-entrant systems. This anomaly is characterised by a large enhancement of the spin-wave damping, a marked change of the transverse static susceptibility which is higher in the 'spin-glass phase' than in the ferromagnetic phase and, at lower temperatures (below 70K), an increase of the stiffness constant. These experimental results are in contradiction with models suggesting a simple break-up of the infinite ferromagnetic network established at TC.
TL;DR: In this article, observations by cw NMR of standing spin-wave resonances in normal liquid were found to agree well with Leggett's theory, and the resonances showed an alternating pattern of frequency shifts, which disappears in the superfluid phase.
Abstract: Observations by cw NMR of standing spin-wave resonances in normal liquid $^{3}\mathrm{He}$ are found to agree well with Leggett's theory. In the superfluid $A$ phase the resonances show an alternating pattern of frequency shifts, which disappears in the $B$ phase.
TL;DR: In this paper, a symmetry classification of the continuous vortices with broken axial symmetry is presented, and it is found that the discrete internal symmetry may in addition be broken in two inequivalent ways, producing two different continuous Vortices.
Abstract: New NMR measurements are reported on continuous $^{3}\mathrm{He}$-$A$ vortices in tilted magnetic fields. We introduce a symmetry classification of the continuous vortices with broken axial symmetry. It is found that the discrete internal symmetry may in addition be broken in two inequivalent ways, producing two different continuous vortices. Although NMR may not distinguish between these two vortices, the observed vortex satellite peak is well accounted for by spin waves localized in the soft core of such vortices.
TL;DR: In this article, the authors performed neutron scattering studies on two very different alloys which undergo transitions from ferromagnetic (FM) to spinglass (SG) states as the temperature is reduced.
Abstract: We have performed neutron scattering studies on two very different alloys which undergo transitions from ferromagnetic (FM) to spin‐glass (SG) states as the temperature is reduced. The alloys are EuxSr1−xS, a crystalline insulator, and (FexMn1−x)75P16B6Al3, an amorphous metal, and their FM‐SG multicritical points are at x≂0.50, T=4 K and x≂0.65, T=42 K respectively. In spite of the substantial differences between these materials, the neutron scattering data show that their spin correlations are remarkably similar. In particular, for the samples near the multicritical points, a single Lorentzian describes the magnetic scattering very well. Its width κ corresponds to a ferromagnetic correlation length ξ which, as T is reduced, first increases to a value indistinguishable from infinity, and then decreases to a finite value, as expected for a ferromagnet which evolves into a reentrant spin glass. As the Fe or Eu content is raised, the scattering function at low temperatures deviates increasingly from the Lore...
TL;DR: In this article, the authors discuss antiferromagnetic bulk and surface spin waves in the long wavelength region on a finite thickness slab geometry and find that the application of a magnetic field strongly localizes the surface spin wave to either the top or bottom surface of the film.
Abstract: We discuss antiferromagnetic bulk and surface spin waves, in the long wavelength region, on a finite thickness slab geometry. Implicit dispersion relations for both surface and bulk modes are derived, along with numerical calculations for MnF2 and GdAlO3. We find that the application of a magnetic field strongly localizes the surface spin wave to either the top or bottom surface of the film.
TL;DR: In this article, it was shown in a microscopic calculation that a translational spin wave mode in an incommensurate spin density wave (SDW) is shown to lead to collective conductivity similarly to the charge density wave case.
Abstract: It is shown in a microscopic calculation that a translational spin wave mode in an incommensurate spin density wave (SDW) is shown to lead to collective conductivity similarly to the charge density wave case. Normal impurities cannot pin the SDW in low orders due to the uniform charge density whereas magnetic impurities give rise to pinning. The pinning frequency due to magnetic impurities is calculated. Possible mechanisms of damping and effects of interchain coupling are briefly discussed.
TL;DR: In this article, the contribution of spin-orbite in terms of interaction spin-orbitite a l'amortissement de Landau-Lifshitz-Gilbert en termes de modele de liaisons fortes de Brooks and de l'approximation de Born pour un desordre diagonal de site is discussed.
Abstract: On discute de la contribution de l'interaction spin-orbite a l'amortissement de Landau-Lifshitz-Gilbert en termes de modele de liaisons fortes de Brooks et de l'approximation de Born pour un desordre diagonal de site
TL;DR: In this article, the results of neutron scattering studies of Cd1-xMnxTe are presented, showing that the low-temperature spin correlations have been studied for several single crystal samples in the composition range 0.60-0.65Te.
Abstract: The diluted magnetic (‘‘semimagnetic’’) semiconductor Cd1–xMnxTe reveals intriguing spin glass properties. In this paper, the results of neutron scattering studies of Cd1–xMnxTe are presented. The low‐temperature spin correlations have been studied for several single crystal samples in the composition range 0.60
TL;DR: In this paper, the Damon-Eshbach theory of surface magnons in a thin ferromagnetic slab is extended to include magneto-crystalline anisotropies of cubic and uniaxial symmetry.
TL;DR: In this article, the spin dynamics of the cerium and uranium monopnictides studied by diffuse and inelastic neutron scattering is reviewed, where the spin wave dispersion is split into two modes of transverse polarization due to the exchange anisotropy.
Abstract: The spin dynamics of the cerium and uranium monopnictides studied by diffuse and inelastic neutron scattering is reviewed. The diffuse scattering above the antiferromagnetic ordering temperature largely corresponds to longitudinal spin fluctuations which are highly anisotropic. For CeAs, CeSb, and UAs multicritical behavior has been found, i.e., the symmetry of the critical scattering above TN differs from the actual type of magnetic ordering below TN. In the ordered state the magnetic excitation spectrum of UN and UAs exhibits only a broad response, whereas well defined spin‐wave branches have been observed for USb and the cerium monopnictides. A very detailed study of the magnetic excitations has been performed for CeAs, where the spin‐wave dispersion is split into two modes of transverse polarization due to the exchange anisotropy. One of these modes exhibits nearly zero energy gap and quadratic dispersion which has not previously been observed in antiferromangets. A generalized random‐phase‐approximat...
TL;DR: Inelastic neutron scattering and neutron polarisation analysis have been used to study the low-temperature spin dynamics of the one-dimensional (1d) ferromagnet CsNiF3 as discussed by the authors.
Abstract: Inelastic neutron scattering and neutron polarisation analysis have been used to study the low-temperature spin dynamics of the one-dimensional (1d) ferromagnet CsNiF3. Measurements were made in the temperature range 2
TL;DR: In this article, the magnetic excitations perpendicular to the antiferromagnetic chains in CsVX 3 (X = Cl, Br, I ) have been measured in the ordered state by inelastic neutron scattering.
TL;DR: In this article, X-ray θ-2θ scans showed that the samples had a bcc (110) texture with a strong composition modulation, which is expected for the Bloch spin wave contribution to the magnetization of a 2D ferromagnet.
Abstract: V/Fe composition‐modulated structures have been grown on the (0001) surface of a sapphire substrate in an UHV evaporator. X‐ray θ‐2θ scans showed that the samples had a bcc (110) texture with a strong composition modulation. Samples with three atomic planes of Fe separated by thick layers of V showed a linear temperature dependence of the saturation magnetization over the range 5–400 K. This behavior is expected for the Bloch spin wave contribution to the magnetization of a 2D ferromagnet. Hysteresis measurements also confirmed that the samples were ferromagnetic. Superconductivity has been seen in samples with very thick V layers.
TL;DR: In this article, the magnetic properties of Mo/Ni matched superlattices were studied and light scattering measurements were performed for the first time to study the Brillouin magnon spectrum.
Abstract: We have studied the magnetic properties of Mo/Ni nonlattice matched superlattices. The dc magnetization was measured in the temperature range 5–300 °K and in magnetic fields up to 10 kG. The saturation magnetization and the Curie temperature behavior are consistent with expectations based on thin film effects. However, there are indications of ferromagnetic coupling across the nonmagnetic metal. Light scattering measurements were performed for the first time to study the magnon spectrum in superlattices. The Brillouin magnon spectra obtained from Mo/Ni superlattices show characteristic features associated with the collective behavior of the superlattice and are in good agreement with earlier theoretical predictions.