Showing papers on "Spin wave published in 1973"
TL;DR: In this paper, the effect of spin fluctuations on itinerant electron ferromagnetism was extended to include the ferromagnetic phase and the correction to the Hartree-Fock free energy as a function of magnetization was expressed in terms of the transversal dynamical susceptibilities.
Abstract: The theory of the effect of spin fluctuations on itinerant electron ferromagnetism, which we have developed previously, is extended to include the ferromagnetic phase. The correction to the Hartree-Fock free energy as a function of magnetization is expressed in terms of the transversal dynamical susceptibilities and is actually calculated by using a modified random phase approximation for the dynamical susceptibilities; the random phase approximation is modified so as to give a consistent static limit throughout the whole temperature range covering both below and above the Curie point. As a result, the magnetization at low temperatures shows a T 3/2 dependence due to the spin wave excitations, the Curie temperature is generally lowered from the Stoner (Hartree-Fock) value and the magnetic susceptibility above the Curie temperature shows an approximate Curie-Weiss behavior.
307 citations
TL;DR: In this article, the spin-wave excitations for nickel have been measured at a series of temperatures between 4.2 and 715 K and it was found that the spin waves change very little in character even at 80 meV above the Curie point, interpreted as the intersection of the spinwave spectra with a continuum band of Stoner excitations.
Abstract: The spin-wave excitations for nickel have been measured at a series of temperatures between 4.2 and 715\ifmmode^\circ\else\textdegree\fi{}K. It is found that the spin waves change very little in character even at 80\ifmmode^\circ\else\textdegree\fi{} above the Curie point. A sudden decrease in the spin-wave intensity at about 80 meV, interpreted as the intersection of the spin-wave spectra with a continuum band of Stoner excitations, is also found to be quite temperature independent.
190 citations
TL;DR: In this paper, the requirements of spin conservation in the form of a Ward identity, are exploited to make a selfconsistent theory of itinerant ferromagnetism in terms of electron-magnon interactions.
Abstract: The requirements of spin conservation in the form of a Ward identity, are exploited to make a selfconsistent theory of itinerant ferromagnetism in terms of electron-magnon interactions. Earlier results are extended to weak ferromagnets and the structure of self energies and single particle spectral weight functions is discussed. The theory is also applied to the calculation of the spin wave stiffness constant.
100 citations
IBM1
TL;DR: In this paper, a relation between the percolation probability, P(s), for site percolations, the conductance, G(x), of certain random networks, and the spin-stiffness coefficient, D(x) of dilute Heisenberg ferromagnet was found.
90 citations
TL;DR: In this article, the eigenvalue equation for the normal modes of excitation of a moving infinite planar magnetic domain wall in an infinite material having the most general second-rank tensor anisotropy is presented.
Abstract: The eigenvalue equation for the normal modes of excitation of a moving infinite planar magnetic domain wall in an infinite material having the most general second-rank tensor anisotropy is presented. The eigenvalues and eigenfunctions of both the spin waves in the presence of the moving wall and the excitation of the wall itself are given to first order in velocity. Cylindrical-domain resonance experiments are proposed to test for the existence of the excitation modes and their effect on domain propagation. The dispersion relation for the wall excitation modes is found to imply a new material requirement for high mobility.
57 citations
TL;DR: In this article, the energy dispersion relation of spin waves in CoCl2 at temperatures between 4.4 K and 34 K was investigated and it was shown that the interplanar exchange interactions are much weaker than those within the planes, giving rise to the'metamagnetic' property of ferromagnetic saturation in relatively weak magnetic fields.
Abstract: Neutron scattering has been used to investigate the energy dispersion relation of spin waves in CoCl2 at temperatures between 4.4 K and 34 K. CoCl2 orders antiferromagnetically at TN=24.9 K with the Co2+ spins lying within ferromagnetic planes which are antiferromagnetically stacked along the hexagonal c axis. The interplanar exchange interactions are much weaker than those within the planes, giving rise to the 'metamagnetic' property of ferromagnetic saturation in relatively weak magnetic fields, and suggesting that above TN there could be correlations between spins appropriate to a two-dimensional ferromagnet. The observed spin waves at low temperature indeed only exhibit strong dispersion within the basal plane and measurement of this dispersion enables an accurate value for the nearest-neighbour exchange constant to be determined.
50 citations
TL;DR: In this paper, the distortions of an Anderson-Morel (AM) phase in terms of Ginzburg-Landau equations are discussed and a new type of singular line (disgyration) is introduced.
48 citations
IBM1
TL;DR: In this article, the implications of magnetic symmetry on the spin-wave spectrum of ferromagnets are examined. And the spinwave dispersion relation is found to contain a term linear in the wave vector for a definite set of magnetic symmetries.
Abstract: The implications of magnetic symmetry on the spin-wave spectrum of ferromagnets are examined. Contrary to the usual result, the spin-wave dispersion relation is found to contain a term linear in the wave vector for a definite set of magnetic symmetries. This linear dispersion is shown to be a consequence of antisymmetric exchange.
47 citations
TL;DR: In this paper, a theory for spin waves in a dilute antiferromagnet has been developed which uses the coherent potential approximation (CPA) to treat the randomly varying Ising interactions between nearest Antiferromagnetic neighbours but treats the off-diagonal parts of the Heisenberg interactions in a more approximate fashion.
Abstract: For pt. I see abstr. A78044 of 1972. A theory for spin waves in a dilute antiferromagnet has been developed which uses the coherent potential approximation (CPA) to treat the randomly varying Ising interactions between nearest antiferromagnet neighbours but treats the off-diagonal parts of the Heisenberg interactions in a more approximate fashion that is consistent with the Goldstone theorem. Although similar to the theory that was found to be successful for K(Co, Mn)F3 and (Co, Mn)F2 in paper I, the problem of the magnetic vacancy requires special treatment. A fictitious spin is placed on the Zn atoms but large potentials are introduced there to prevent the spin waves from propagating via these sites. The Green functions, neutron scattering and Raman scattering have been calculated.
42 citations
TL;DR: The first report of the ferromagnetic resonance properties of thin single-crystal YIG films grown by liquid phase epitaxy techniques (LPE) was given in this paper, where the resonance linewidths of photoetched disks are close to that of bulk YIG for both parallel and perpendicular resonance without any annealing of the films.
Abstract: This is the first report of the ferromagnetic resonance properties of thin single-crystal YIG films grown by liquid phase epitaxy techniques (LPE). The resonance linewidths of photoetched disks are close to that of bulk YIG for both parallel and perpendicular resonance without any annealing of the films. A new type of surface spin wave, localized at the air-film interface, is shown to exist in perpendicular resonance. The boundary conditions necessary for this surface spin wave to exist are produced either by SiO 2 sputtering or ion implantation.
35 citations
TL;DR: In this paper, the free energy, magnetizations, susceptibilities, specific heat and entropy of the Ising model in a transverse field Gamma are calculated as functions of temperature and field by expanding in ascending powers of the high-density parameter 1/z.
Abstract: The free energy, magnetizations, susceptibilities, specific heat and entropy of the Ising model in a transverse field Gamma are calculated as functions of temperature and field by expanding in ascending powers of the high-density parameter 1/z. For each of these quantities the leading-order term (molecular-field theory) is written down and the first-order corrections, proportional to (1/z)1, are derived and described. Spin wave and spin fluctuation effects occur in the first-order corrections. These include zero-point terms and linear spin wave effects as well as effects arising from the temperature and field dependence of the spin wave energies. These latter effects are particularly important at the critical temperature Tc( Gamma ) where the spin wave energy vanishes. This results in a first-order specific heat contribution showing a change from exponential to T3 temperature dependence when both T and Tc( Gamma ) are small. The zero-point terms are directly measurable in, for example, the curvature of the transverse magnetization as a function of Gamma at very low temperatures.
TL;DR: In this article, a detailed discussion of the generalized susceptibilities and spectral functions rho alpha beta of the Ising model in a transverse field Gamma is provided, and the leading contributions to the damping of the excitations as well as the first-order shift in their energy and in the critical temperature are obtained.
Abstract: For Pt. I see ibid., vol. 6, no. 15, 2459 (1973). By taking the (1/z) expansion one order beyond that considered in Pt. I, a detailed discussion is provided of the generalized susceptibilities and spectral functions rho alpha beta of the Ising model in a transverse field Gamma . The leading contributions to the damping of the excitations as well as the first-order shift in their energy and in the critical temperature, are obtained. The damping arises from break-up into (i) a spin wave and a spin fluctuation or (ii) a pair of spin waves.
TL;DR: By inelastic neutron scattering from CsNiF 3 at 4.2 K spin waves in a one-dimensional ferromagnet, the dispersion relation can be described by only nearest neighbour interaction and follows the relation ν = 0.09 + 0.98 [1 − cos ( π qc )] THz as discussed by the authors.
TL;DR: In this article, an equation for the energy levels of the spin Hamiltonian for low symmetry was given, and the angular dependence of the transition probability up to first order was given for randomly oriented samples.
TL;DR: In this article, a method of calculating the long wavelength spin wave frequencies in a multiple band itinerant antiferromagnet is described, and the frequencies are derived by examining the poles of the RPA generalized susceptibility for the d electrons.
Abstract: A method of calculating the long wavelength spin wave frequencies in a multiple band itinerant antiferromagnet is described. No special features of the band structure, such as nesting, are assumed. The frequencies are derived by examining the poles of the RPA generalized susceptibility for the d electrons. A natural consequence of the treatment is the existence of a spin wave damping proportional to the wavevector. This is attributed to the decay of the spin wave into an electron-hole pair. The formulae are applied numerically to gamma manganese. Rough agreement with experiment is found.
TL;DR: In this article, the neutron inelastic scattering cross section is accurately calculated at low temperature in a special model for one-and two-dimensional media for magnons in a magnetically disordered medium with any wavelength at sufficiently low temperature.
Abstract: With a suitable definition, magnons can exist in a magnetically disordered medium with any wavelength at sufficiently low temperature, but they can only be observed by neutron scattering at small wavelengths. The neutron inelastic scattering cross section is accurately calculated at low temperature in a special model for one- and two-dimensional media.
TL;DR: In this paper, the authors measured spin wave resonance for a series of fcc Fe-Ni alloys in order to study the exchange stiffness constant D, which is considered to be due to the inhomogeneous demagnetizing field of the sample.
Abstract: Spin wave resonance for a series of fcc Fe-Ni alloys has been measured in order to study the exchange stiffness constant D . In general the resonance field vs the square of the spin wave mode number ( n ) curve is linear for high values of n , whereas some amount of deviation from linearity occurs for low values of n . This is considered to be due to the inhomogeneous demagnetizing field of the sample. We can determine the value of D from the linear part of the curve, provided we have a sufficient number of observed modes. As a supplementary means, we have also made low temperature magnetization measurements from which the value of D was derived. Consistency between these two kinds of measurements is ascertained. The composition dependence of D is not quite coincident with that derived from the neutron small angle scattering experiments by Hatherly et al. The data are discussed both from the standpoint of localized electron model and collective electron model.
TL;DR: In this paper, a single crystal of ferromagnetic MnAlGe was measured from 4.2 K to 350 K in order to determine the uniaxial magnetic anisotropy constant K 1.
Abstract: Magnetization measurements were made on a single crystal of ferromagnetic MnAlGe from 4.2 K to 350 K in order to determine the uniaxial magnetic anisotropy constant K 1 . The saturation moment and K 1 extrapolated to 0 K are 1.70 µ B /Mn and 9.7×10 6 erg/cc, respectively. The observed temperature dependence of K 1 , after corrected for dipole-dipole interaction energy, is expressed in terms of the saturation magnetization σ as 10.7×10 6 [σ( T )/σ(0)] 3.08 erg/cc, in good agreement with the spin wave theory which predicts the exponent 3.
TL;DR: In this article, the theoretical conditions for surface mode detection in spin wave resonance (SWR) spectra are discussed. And a criterion for identifying surface peaks in SWR spectra is proposed.
Abstract: Of late, the number of papers on magnetic surface states has greatly increased since the experimental detection of these states has been proven to open up a highly promising source of abundant data on the magnetic properties of materials. Spin wave resonance (SWR)-an effect observed in thin ferromagnetic films-is well adapted for such detection. In this paper, we are concerned with the theoretical conditions for surface mode detection in SWR. Since SWR depends essentially on the conditions existing on the surfaces of a film, we begin with a closer analysis of the concept of surface spin pinning. Next, resorting to the Surface Inhomogeneity Model (thin film, totally homogeneous within, but presenting arbitrary asymmetric conditions on its surfaces), we solve the problem of the existence of surface modes as a function of the pinning conditions, and discuss the essential features of these modes. Finally, we propose a criterion for identifying surface peaks in SWR spectra.
TL;DR: In this article, the derivation of characteristic surfaces for interacting higher spin wave equations is discussed in a shock wave formalism, and the propagation of shock waves along the bicharacteristics are established for several interacting systems.
Abstract: The derivation of characteristic surfaces for interacting higher spin wave equations is discussed in a shock wave formalism. Equations describing the propagation of shock waves along the bicharacteristics are established for several interacting systems.
TL;DR: In this article, an expression for the spin wave stiffness constant D in a ferromagnetic alloy using essentially the random phase approximation was derived for NiFe and NiCo alloys.
Abstract: An expression is derived for the spin wave stiffness constant D in a ferromagnetic alloy using essentially the random phase approximation. On applying the coherent potential approximation a result previously derived by Fukuyama (1973) is obtained. Numerical calculations are made for NiFe and NiCo alloys.
TL;DR: In this paper, the authors measured the magnetic resonance in nickel platelets as a function of the orientation of the sample at room temperature and found that the line width indicates a strong dependence on the angle between the applied magnetic field and the normal to the film plane, which they described as a sum of a constant term and a term resulting from the Gilbert type equation of motion.
Abstract: Ferromagnetic resonances in nickel platelets were measured as a function of the orientation of the sample at room temperature. The line width indicates a strong dependence on the angle between the applied magnetic field and the normal to the film plane. The dependence can be well described as a sum of a constant term and a term resulting from the Gilbert type equation of motion. No spin wave resonance was observed.
TL;DR: In this article, the authors studied the variational treatment of spin waves in the randomly diluted Heisenberg ferromagnet at zero temperature and obtained a second-order variational bound for the spin-wave energy which, unlike that found by Murray, is positive at all concentrations.
Abstract: The variational treatment of spin waves in the randomly diluted Heisenberg ferromagnet at zero temperature is studied. It is argued that a convenient variational principle for the excitation spectrum of an alloy is difficult to formulate rigorously. However, at extremely long wavelengths a simple variational calculatation probably has approximate validity providing localized excitations in isolated clusters of magnetic sites are excluded. Within the approximation which ignores this exclusion we obtain a second-order variational bound for the spin-wave energy which, unlike that found by Murray, is positive at all concentrations. Similar results for concentrations above the critical percolation concentration ${x}_{p}$ are obtained when the localized excitations are excluded in which case the restricted configuration averages can only be evaluated approximately. We point out that the critical concentration ${x}_{c}$ for the occurance of long-range order depends only on the properties of the infinite cluster. Thus the thermal stability of spin waves depends on the dimensionality of the infinite cluster. An argument is given to show that the infinite cluster is not one dimensional. The range of concentrations for which the infinite cluster is two dimensional is either nonexistent or small. We conclude, then, that ${x}_{c}$ is close, if not exactly equal, to ${x}_{p}$. The condition for a discontinuity in ${T}_{C}(x)$ for $x\ensuremath{\rightarrow}{x}_{c}$ is discussed in terms of a simple periodic model for dilution.
TL;DR: In ferromagnetic resonance experiments of yttrium-iron-garnet films, resonances have been observed whose characteristics are consistent with their interpretation as magnetostatic surface spin wave modes as mentioned in this paper.
TL;DR: In this paper, the magnetoelastic-mode theory of easy-plane hexagonal ferromagnets is approached from general principles of small oscillations around the equilibrium configuration, and a general formula for normal-mode energies is obtained by diagonalizing the Hamiltonian, properly retaining terms quadratic in magnon-magnon, phonon-phonon, and magon-aphon operators.
Abstract: The magnetoelastic-mode theory of easy-plane hexagonal ferromagnets is approached from general principles of small oscillations around the equilibrium configuration. A general formula for normal-mode energies is obtained by diagonalizing the Hamiltonian, properly retaining terms quadratic in magnon-magnon, phonon-phonon, and magon-phonon operators. It is found that magnons and phonons are strongly mixed in the region of small $k$ for transverse waves propagating in certain directions parallel to the hexagonal plane when an external field is applied along the hexagonal hard direction and is close to $\frac{36{K}_{h}}{M}$ (hexagonal anisotropic field). On the other hand, the spin waves propagating along the $c$ axis are well approximated by the Turov-Shavrov frozen-lattice model because the extremely strong axial anisotropy makes the dynamical interaction (quadratic magnon-phonon terms) diminished. The dipolar effect is also discussed; and it is shown that, in the hard-direction case, magnons and phonons are mixed in relatively small amounts for the transverse waves propagating perpendicular to the magnetization, owing to the volume dipolar effect. Application of our theory to Tb is made with the use of numerical values of the temperature-dependent anisotropic and magneto-elastic coupling parameters. The lower-branch magnetoelastic modes may be responsible for the absorption of microwaves in the low-frequency-resonance experiments.
TL;DR: Gutzwiller's variational method is used to investigate the Pauli spin susceptibility and the spin waves in a degenerate narrow band as mentioned in this paper, and it is found that the susceptibility tends to become negative for sufficiently strong correlation if the number of holes is small and if large density of states occurs at the top of the band near the Fermi energy.
Abstract: Gutzwiller's variational method is used to investigate the Pauli spin susceptibility and the spin waves in a degenerate narrow band. It is found that the susceptibility tends to become negative for sufficiently strong correlation if the number of holes is small and if large density of states occurs at the top of the band near the Fermi energy. For Ni, a numerical analysis is performed using the simplified density-of-states curve proposed by Kanamori. The conditions for the occurrence of ferromagnetic Ni agree with those obtained by Kanamori. The energies of spin waves in ferromagnetic metals are obtained by examining the normal modes of spin excitations in the correlated ground state. Only the improvement upon the random-phase-approximation (RPA) result which is due to correlated electron hoppings is considered. In the long-wavelength limit, the coefficient $C$ in the expression $\ensuremath{\hbar}{\ensuremath{\omega}}_{q}=C{q}^{ 2}$ is reduced from the RPA value by this correlation effect, in agreement with the predictions of other theories.
TL;DR: In this paper, the Hartree-Foch approximation of magnon renormalization was extended to spin precession in highly anisotropic ferromagnets, which is a feature of the theory of magnetoelastic magneto-graphs.
Abstract: For pt.I see abstr. A24581 of 1973. Magnon energies, renormalized in a Hartree-Foch approximation, have been derived. The model includes isotropic and anisotropic exchange interactions, a crystal field of HCP symmetry, magnetoelastic interactions and dipolar interactions. The novel feature of the theory is a modification of magnon renormalization by the ellipticity of spin precession that is a characteristic of highly anisotropic ferromagnets.