Showing papers on "Spin wave published in 1977"
TL;DR: In this paper, the hydrodynamic theory of spin waves is extended to a magnetic system such as a spin glass or a crystal with helical spin order, in which there are equilibrium magnetizations on different sites, with spin directions that are not collinear.
Abstract: The hydrodynamic theory of spin waves is extended to a magnetic system such as a spin glass or a crystal with helical spin order, in which there are equilibrium magnetizations on different sites, with spin directions that are not collinear. If the total magnetization is zero and if the interactions are assumed to be isotropic in spin space, one predicts well-defined spin waves at small wave vectors $\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}$, with a linear dispersion relation, and three polarizations for each value of $\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}$. The hydrodynamic assumption of a finite spin-stiffness constant may be questionable, however, for the spin glass. Nonzero magnetization is discussed briefly.
169 citations
TL;DR: In this paper, the electrical resistivity of antiferromagnetic metals is discussed on the basis of the two band model and the general expression in terms of the dynamical susceptibility is obtained.
Abstract: The electrical resistivity of antiferromagnetic metals is discussed on the basis of the two band model. The general expression in terms of the dynamical susceptibility is obtained. The resistivity is studied by using the self-consistent renormalization theory of spin fluctuations. The resistivity at low temperatures is proportional to T 2 and its coefficient diverges as |α-1| -1/2 as one approaches the critical boundary of antiferromagnetism. It is pointed out that in the ordered phase the effect of the gap in the conduction band is important. Especially, this effect plays a crucial role in the temperature dependence of the contribution of the spin waves. It is proportional to T 5 and T 2 at the temperatures lower and higher, respectively, than the gap energy. At high temperatures the resistivity is significantly suppressed from that calculated by using RPA results for the spin fluctuations and can have a tendency towards saturation.
94 citations
TL;DR: In this paper, light-scattering experiments on thermal acoustic spin waves in EuO were conducted and two peaks which can be shifted by an external magnetic field were identified as due to a modified bulk spin wave of the material.
Abstract: We present results of light-scattering experiments on thermal acoustic spin waves in EuO. The Brillouin spectra show two peaks which can be shifted by an external magnetic field. One of these is identified as due to a modified bulk spin wave of the material. The other one, by its anomalous behavior on reversal of the magnetic field or change of the scattering geometry, reveals itself as a spin wave propagating along the surface of the crystal.
89 citations
TL;DR: In this article, a spin-wave resonance at 10 GHz was observed in thin garnet films of approximate composition Y2.85La0.15Fe3.75Ga1.25O12.
Abstract: Spin‐wave resonance at 10 GHz has been observed in thin (? 5 μm) garnet films of approximate composition Y2.85La0.15Fe3.75Ga1.25O12. The films were grown by LPE on [111]‐oriented gadolinium gallium garnet substrates, both from a nonstirred melt (vertical mode of dipping) and a stirred melt (horizontal dipping, applying axial substrate rotation). The spectra exhibit large numbers of strongly excited modes with large deviations from quadratic spacing, which are interpreted in terms of a volume inhomogeneity of the uniaxial anisotropy constant Ku. Two models are used to explain the experimental spectra. In one model the film is considered as being built up of exchange coupled layers having different uniaxial anisotropy constants Ku. In the second model it is assumed that Ku varies linearly with the distance from the substrate, but with different slopes in different regions. No pinning is assumed at the surfaces. A simple graphical method is presented for determining the normal modes of films with these types...
88 citations
TL;DR: In this paper, the spin wave dispersion relations along three principal directions were systematically explored across the whole magnetic Brillouin zone at 4 K, and the results were analyzed using the Heisenberg Hamiltonian with long range magnetic interactions.
Abstract: The spin waves in a Heusler alloy Cu 2 MnAl were investigated at several temperatures by neutron inelastic scattering. The spin wave dispersion relations along three principal directions were systematically explored across the whole magnetic Brillouin zone at 4 K. The results were analysed using the Heisenberg Hamiltonian with long range magnetic interactions. At T =493 K ( T / T c =0.78), the renormalization of the spin wave energy at large momentum transfer regions was found to be very small. This result is interpreted in terms of the temperature dependence of the s - d interaction at large distances.
66 citations
TL;DR: In this article, the magnetic, thermal and magnetoelastic properties of strong and weak ferromagnets are discussed from the point of view of elementary thermodynamics, and a critical index τ relating Tc with the Stoner factor is shown from the evidence to be close to 1 2.
Abstract: The magnetic, thermal and magnetoelastic properties of strong and weak ferromagnets are discussed from the point of view of elementary thermodynamics. This is shown to provide a valuable link between the emperical evidence and quantum mechanics. It is concluded on this basis that strong itinerant ferromagnets, in particular nickel, have properties below the Currie point governed mainly by spin waves. For weak itinerant ferromagnets the evidence for the dominance of single particle excitations is very much stronger. A critical index τ relating Tc with the Stoner factor as ( I - 1)τ is shown from the evidence to be close to 1 2 .
59 citations
TL;DR: In this article, the spatial variation of the order parameter of the B phase of /sup 3/He is studied and the effect of these textures on nuclear magnetic resonance is discussed and it is shown that the textures should allow one to observe standing spin waves as well as the line shape effects discussed in an earlier letter.
Abstract: The nature of the spatial variation of the order parameter of the B phase of /sup 3/He is detailed. It is shown that in this phase there is a single vector component of the order parameter which undergoes spatial variation under normal circumstances and the detailed nature of its variation is calculated for cylindrical and parallel-plate geometries. The effect of these textures on nuclear magnetic resonance is discussed and it is shown that the textures should allow one to observe standing spin waves as well as the line-shape effects discussed in an earlier letter. (AIP)
54 citations
TL;DR: In this article, it was shown that low-temperature spin waves in classical spin systems can be understood in terms of a fixed-length hydrodynamic theory, which is exactly soluble in one and two dimensions for models with an easyplane anisotropy.
Abstract: We suggest that low-temperature spin waves in classical spin systems can be understood in terms of a "fixed-length" hydrodynamic theory. A theory is constructed along these lines which is exactly soluble in one and two dimensions for models with an easy-plane anisotropy. The results should apply at low temperatures to one-dimensional ferromagnets such as CsNi${\mathrm{F}}_{3}$, and agree with a microscopic truncated-spin-wave theory proposed by Villain. In two dimensions, we expect the calculations to be valid in a band of temperatures for $\mathrm{XY}$ magnets with an underlying hexagonal symmetry. The calculations should describe in addition the long-wavelength, low-frequency dynamics of third-sound propagation in films of $^{4}\mathrm{He}$ and $^{3}\mathrm{He}$-$^{4}\mathrm{He}$ mixtures. We also show that the critical exponent $\ensuremath{
u}$ is $\ensuremath{
u}\ensuremath{\approx}\frac{1}{2\sqrt{\ensuremath{\epsilon}}}$ for $\mathrm{XY}$ models in $2+\ensuremath{\epsilon}$ dimensions. Some results for dynamics in three dimensions are presented as well.
53 citations
IBM1
TL;DR: The magnetic specific heat of amorphous GdAl 2 shows a broad maximum near 17.5 K, the temperature of the spin-glass-like cusp in the magnetic susceptibility.
46 citations
TL;DR: In this article, a complete eigenfunction expansion for the Hamiltonian of the spin 1/2 Heisenberg chain in this representation, for all numbers of spin waves, was given.
Abstract: In its ground state representation, the infinite, spin 1/2 Heisenberg chain provides a model for spin wave scattering, which entails many features of the quantum mechanicalN-body problem. Here, we give a complete eigenfunction expansion for the Hamiltonian of the chain in this representation, forall numbers of spin waves. Our results resolve the questions of completeness and orthogonality of the eigenfunctions given by Bethe for finite chains, in the infinite volume limit.
45 citations
TL;DR: In this paper, the temperature and the field dependence of the law of approach to ferromagnetic saturation were investigated in amorphous Fe40Ni40P14B6-alloys.
TL;DR: In this paper, the spin wave dispersion in the planar 1D ferromagnet CsNiF3 has been measured by inelastic neutron scattering in an external field.
Abstract: The spin wave dispersion in the planar 1D ferromagnet CsNiF3 has been measured by inelastic neutron scattering in an external field. The spin wave linewidths are found to decrease with increasing field and become resolution-limited for H>10 kG at 4.2K. At high fields, H>10 kG, both energies and intensities are found to follow linear spin wave theory. The analysis resolves a discrepancy between the anisotropy constants, A, derived earlier from spin-wave and susceptibility measurements, respectively. It turns out that a quantum correction is necessary in order to get consistent parameters. Two parameters namely the nearest-neighbour exchange, J/k=11.5+or-0.05K and A/k=8.9+or-0.2K, are needed to fully describe the system. The temperature dependence of the spin waves in an external field was also studied.
TL;DR: In this paper, the exact solution for the spin-wave spectrum of the S = 1/2 antiferromagnetic Heisenberg chain is extended to the case of finite external field.
Abstract: The des Cloizeaux and Pearson's exact solution for the spin-wave spectrum of the S=1/2 antiferromagnetic Heisenberg chain is extended to the case of finite external field. It reproduces naturally the des Cloizeaux-Pearson spectrum in the zero-field limit as well as the spin-wave spectrum in the ferromagnetic state for fields larger than the critical field. The results are discussed by comparing them with predictions of other approximate theories. on CuC12 • 2NC,D,, which is a typical 1D antiferromagnetic Heisenberg spin system with S = 1/2. They showed by neutron scattering that its spin-wave spectrum agrees quite well with the celebrated exact solution of des Cloizeaux and Pearson ( dC-P) ;l and is in disagreement with the Anderson (molecular-field) theory. It clearly demonstrates the importance of exact theoretical studies of 1D systems. Although this experiment was made in the absence of external magnetic field, the magnetic-field dependence of elementary excitations in antiferromagnetic linear chains would be very interesting. The purpose of this paper is to study exactly the magnetic-field dependence of the dC-P spin-wave spectrum. We hope that this work would stimulate further experimental studies on dynamics of 1D Heisenberg antiferromagnets in the presence of external field. The field dependence of spin waves of lD Heisenberg antifer romagnets has previously been calculated by Pytte,"l who applied the Bulaevskii (Hartree-Fock) approximation') based on the Fermion representation 5l.Bl of the lD Heisenberg model. We later compare it with our result. We also show that the magnetic-field dependence of the dC-P spin wave is qualitatively different from that of the classical (Anderson) spin wave. The details of the formulation and calculations are presented in § 2. Com-
TL;DR: In this article, a complete eigenfunction expansion for the Hamiltonian of the spin 1/2 Heisenberg chain in this representation, for all numbers of spin waves, was given.
TL;DR: In this paper, a new scattering mechanism for the resistivity based on electron low-lying collective mode (spin wave like) collisions was proposed for TTF-TCNQ and all derivative compounds.
Abstract: We propose a new scattering mechanism for the resistivity based on electron low-lying collective mode (spin wave like) collisions. This scattering is particularly efficient in TTF-TCNQ as magnetic ordering is nearly achieved in this material under ambient conditions (U/4 t∥ ~ 1). Also it provides a theoretical quasi-linear temperature dependence at constant b-axis together with the essential connection noticed between conductivity and magnetism in TTF-TCNQ and all derivative compounds.
TL;DR: In this article, the anisotropic exchange interaction between localized spins and conduction electrons is described by an appropriate spin hamiltonian, which is used to calculate the lifetime of magnons for arbitrary values of Λ eq, where q is the magnon wavevector.
TL;DR: In this paper, the magnetic excitations in amorphous ferromagnet Fe/sub 75/P/sub 15/C/sub 10/C were measured using neutron-scattering techniques.
Abstract: Neutron-scattering techniques have been used to measure the magnetic excitations in the amorphous ferromagnet Fe/sub 75/P/sub 15/C/sub 10/. Triple-axis measurements show a distinct spin-wave excitation at small momentum transfers that closely obeys a quadratic dispersion relation E = DQ/sup 2/ for D equal to about 120 meV A/sup 2/. Time-of-flight polarized-beam measurements made in the vicinity of the first peak in S (Q) near 3 A/sup -1/ show excitations that reach a minimum energy at the maximum in S (Q). These excitations are similar to the roton excitations in /sup 4/He except that they are rather broad in energy since they are able to decay into single-particle states. A contour map is presented which shows the scattering measurements in the neighborhood of 3 A/sup -1/ and the results are compared with calculations of magnetic excitations in amorphous systems.
TL;DR: In this paper, a detailed quantitative study of the low-temperature spin-wave dynamics has been made for the classical Heisenberg-coupled chain using computer simulation and results for the relaxation rates are presented and compared with dynamic scaling and other predictions.
Abstract: A detailed quantitative study of the low-temperature spin-wave dynamics has been made for the classical Heisenberg-coupled chain using computer simulation. Results for the relaxation rates are presented and compared with dynamic scaling and other predictions.
TL;DR: In this article, a generalized Hartree-Fock treatment of paramagnon-paramagnon interactions of all orders is proposed, where the susceptibility χ( q, ω) is expressed in the form χ 0 ( q, ω)[1 − 2 3 3 ] − 1, where χ is an average of the susceptibility of the noninteracting system over a maxwellian distribution of fluctuating magnetic fields.
Abstract: We show how fairly well-defined sloppy spin waves can arise in itinerant ferromagnets above the Curie point, by making a generalized Hartree-Fock treatment of paramagnon-paramagnon interactions of all orders. By treating these interactions as approximately local, one may express the susceptibility χ( q , ω) in the form χ 0 ( q , ω)[1 − 2 3 U χ 0 ( q , ω)] -1 , where χ 0 is an average of the susceptibility of the noninteracting system over a maxwellian distribution of fluctuating magnetic fields. The consequent fluctuating Stoner gap can lead to fairly well-defined propagating excitations in a limited range of wavenumbers.
IBM1
TL;DR: In this article, the Coulomb repulsion between noninteracting electrons was used to increase the magnitude of the magnetic susceptibility and its effect on the NMR relaxation rate of TTF-TCNQ.
Abstract: In this article we demonstrate that Coulomb interactions play a major role in the solid state properties of TTF-TCNQ. We start by considering a model of non-interacting electrons and then examine the new features caused by adding the strong Coulomb repulsion between these electrons. These new features include:
(1)
The appearance of a new optical excitation whose energy is a measure of the strength of the effective Coulomb interaction;
(2)
An enhancement in the magnitude of the magnetic susceptibility and effects on the NMR relaxation rate;
(3)
The decoupling of spin and translational degrees of freedom and hence the appearance of spin waves; and
(4)
The doubling of the characteristic wavevector of the charge excitations, from 2k F o to “4k F o ”.
TL;DR: A set of harmonic-oscillator-like spin wave modes have been observed in superfluid 3 HeB confined by a set of parallel plates as discussed by the authors, and the frequencies and intensities of these modes are in close agreement with computer solutions of the theoretical equations.
Abstract: A set of harmonic-oscillator-like spin wave modes has been observed in superfluid 3 HeB confined by a set of parallel plates. The frequencies and intensities of these modes are in close agreement with computer solutions we have obtained of the theoretical equations. Both the experimental results and the computer solutions are discussed in detail.
TL;DR: In this paper, the influence of quasi spin wave interactions on the infrared singularity in magnetic chains with XY symmetry was investigated, and the leading anharmonic corrections to the characteristic frequency and exponent of the IR singularity were given.
Abstract: We investigate the influence of quasi spin wave interactions on the infrared singularity in magnetic chains with XY symmetry. The interactions considered contribute to a smearing of the infrared singularity only when a smearing due to the nonlinearity of the spectrum is present. The leading anharmonic corrections to the characteristic frequency and exponent of the infrared singularity are given.
TL;DR: In this article, the spin excitations in a single crystal of Cr/sub 0.98/Mn/sub 1.02/ have been studied by inelastic neutron scattering.
Abstract: The spin excitations in a single crystal of Cr/sub 0.98/Mn/sub 0.02/ have been studied by inelastic neutron scattering. High-resolution triple-axis spectrometer measurements have yielded a value of the spin-wave velocity at T/T/sub N/ approx. = 0.5 of (1.30 +- 0.15) x 10/sup 7/ cm/sec in good agreement with earlier measurements. The excitation strength drops extremely rapidly in the vicinity of T/sub N/ and decreases approximately linearly above T/sub N/. The spin-wave form factor has been measured below and above T/sub N/ by measuring the spin-wave intensity at various superlattice points, and is found to agree to within experimental error with the static spin form factor. The implications of these results for the theory of itinerant electron antiferromagnetism are discussed. (AIP)
TL;DR: In this article, it was shown that a random Heisenberg magnet characterized by H = 1/2 Sigma iJij xi i xi jSiSj, where Jij is a fixed function of the separation of sites i and j but the sites i are randomly +or-1, can sustain well defined longwavelength spin waves with an antiferromagnetic-like linear dispersion.
Abstract: It is shown that a random Heisenberg magnet characterized by H=1/2 Sigma iJij xi i xi jSiSj, where Jij is a fixed function of the separation of sites i and j but the xi i are randomly +or-1, can sustain well defined long-wavelength spin waves with an antiferromagnetic-like linear dispersion
[...]
TL;DR: In this article, a set of harmonic-oscillator-like standing spinwave modes have been observed in a superfluid regime, where the frequencies and intensities of the modes are in close agreement with computer solutions of the theoretical equations.
Abstract: A set of harmonic-oscillator-like standing spin-wave modes have been observed in superfluid $^{3}\mathrm{He}$-$B$ confined by a set of parallel plates. The frequencies and intensities of the modes are in close agreement with computer solutions of the theoretical equations. Their observation represents the first direct confirmation of the existence of spin-wave dispersion in either superfluid phase of $^{3}\mathrm{He}$.
TL;DR: In this article, the lineshapes associated with light scattering by spin-waves in absorptive (semi-opaque) magnetic materials at low temperatures were investigated and shown to be asymmetric and there is an "opacity broadening" contribution to their width.
Abstract: Calculations are presented for the lineshapes associated with light scattering by spin-waves in absorptive (semi-opaque) magnetic materials at low temperatures. Scattering at normal incidence to the surface is considered, and it is predicted that the lineshapes are asymmetric and that there is an 'opacity broadening' contribution to their width. Both ferromagnetic and antiferromagnetic materials are considered, although it is shown that the effects may be considerably larger in antiferromagnets with small anisotropy. The theory is applied to obtain numerical results for the antiferromagnets RbMnF3 and MnF2.
TL;DR: In this paper, the nuclear spin-lattice relaxation time T1 of 45Sc and electrical and thermal resistivities in an itinerant electron ferromagnet Sc3In were measured in both ferromagnetic and paramagnetic states as a function of magnetic field strength.
Abstract: The nuclear spin-lattice relaxation time T1 of 45Sc and electrical and thermal resistivities in an itinerant electron ferromagnet Sc3In were measured in both ferromagnetic and paramagnetic states as a function of magnetic field strength. The observed magnetic field dependence of (T1T)-1 and negative magnetoresistivities in both states are explained very well by the self-consistently renormalized spin fluctuation theory in which the effect of magnetic field was taken into account. These experimental results support the spin fluctuation theory and suggest the importance of the effect of magnetic field on spin fluctuations.