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Showing papers on "Spin wave published in 1976"


Journal ArticleDOI
TL;DR: In this article, the magnetic interactions in Heusler alloys Pd 2 MnSn and Ni 2 NMSn have been investigated using neutron spin wave scattering using a Heisenberg Hamiltonian where only Mn atoms have a localized moment.
Abstract: The magnetic interactions in Heusler alloys Pd 2 MnSn and Ni 2 MnSn have been investigated using neutron spin wave scattering. The spin wave dispersion relations along the [00ζ], [ζζ0] and [ζζζ] directions have been observed across the whole magnetic Brillouin zone. The results have been analyzed using a Heisenberg Hamiltonian where only Mn atoms have a localized moment. It has been found that the interactions between more than 6th neighbors should be taken into account to reproduce the observation. The exchange constants at large distances have an oscillatory character which can be interpreted by the s - d type interactions based on the nearly free electron model. However, the n . n . and n . n . n . interactions have signs opposite to those expected from the simple s - d model. The n . n . and n . n . n . exchange constants in Ni 2 MnSn ( T C =344 K) are larger than those in Pd 2 MnSn ( T C =189 K), although the oscillatory parts have nearly the same values for both alloys.

104 citations


Journal ArticleDOI
TL;DR: Inelastic neutron scattering has been used to investigate the spin dynamics of the isotropic Heisenberg ferromagnet EuO over a wide range of wave vectors and over a temperature range extending from 0.14 to 1.9°C.
Abstract: Inelastic neutron scattering has been used to investigate the spin dynamics of the isotropic Heisenberg ferromagnet EuO over a wide range of wave vectors and over a temperature range extending from 0.14 to $1.9{T}_{C}$. Below the ordering temperature spin-wave renormalization is found to agree well with the predictions of Dyson-Maleev theory (including the dynamical but not the kinematical interaction) when both exchange and dipolar couplings between the ${\mathrm{Eu}}^{2+}$ ions are taken into account. At temperatures near ${T}_{C}$ broadening of the spin-wave lines was observed. For hydrodynamic spin waves, the wave-vector dependence of the linewidths is found to be consistent with the expectations of microscopic spin-wave theory and the temperature dependence with predictions based on dynamical scaling. At ${T}_{C}$, linewidths were found to deviate from the ${q}^{\frac{5}{2}}$ wave-vector dependence expected on the basis of dynamical scaling arguments when only exchange couplings are taken into consideration. But when dynamical scaling theory is modified by including dipolar interactions, it satisfactorily accounts for the weaker $q$ dependence observed experimentally. Current microscopic theories appear to overestimate the magnitudes of the linewidths at ${T}_{C}$ although above ${T}_{C}$ theory properly predicts the temperature dependence of the spin diffusion coefficient in the hydrodynamic regime and also provides a good estimate of its magnitude.

96 citations


Journal ArticleDOI
TL;DR: In this paper, temperature dependences of spin wave energies, the integrated intensity of neutron scattering, as well as the magnetization of a single crystal of Pd 2 MnSn have been measured.
Abstract: Temperature dependences of spin wave energies, the integrated intensity of neutron scattering, as well as the magnetization of a single crystal of Pd 2 MnSn have been measured. The results have been found to be well interpreted in terms of the spin wave theory including magnon-magnon interactions developed for the Heisenberg system. Neutron paramagnetic scattering from the same crystal has also been measured at 300 and 1000 K. The second moment determined from the energy spectra of Gaussian shape is in good agreement with that calculated using the exchange parameters determined by spin wave measurement at 50 K. These results indicate that the Heusler alloy is a typical Heisenberg system with long range interactions.

51 citations


Journal ArticleDOI
TL;DR: In this paper, the lattice term, C L was obtained from the C P data of LuAl 2 by a method of interpolation which gave values of C L for an arbitrary R Al 2 compound.

43 citations


Journal ArticleDOI
TL;DR: In this paper, the authors measured the spin-wave spectrum from 2 to 14 K, and found an exchange integral of 11.4 K between the first neighbours in the basal plane, and no measurable dispersion was found along the axis perpendicular to that plane.

43 citations


Journal ArticleDOI
TL;DR: In this article, the magnon dispersion relation for the ferrimagnetic cubic Laves compound Ho/sub 0/./sub 88/Tb/Sub 0/sub 12/Fe/sub 2/ at room temperature and 12 K was investigated.
Abstract: Using neutron spectrometey, we have investigated the magnon dispersion relation for the ferrimagnetic cubic Laves compound Ho/sub 0/./sub 88/Tb/sub 0/./sub 12/ Fe/sub 2/ at room temperature and 12 K. The results are described surprisingly well by a very simple near-neighbor exchange model which includes only iron--iron and iron--rare-earth interactions, crystal field anisotropy, and temperature renormalization that is derived from the sublattice magnetization. (AIP)

40 citations


Journal ArticleDOI
Tôru Moriya1
TL;DR: In this paper, the dynamical susceptibilities of itinerant electron ferromagnets above T C are treated by taking account of the coupling among the spin fluctuation modes to a greater extent than was made before.
Abstract: The dynamical susceptibilities of itinerant electron ferromagnets above T C are treated by taking account of the coupling among the spin fluctuation modes to a greater extent than was made before and the relatively short wave components are shown to have characteristics of spin waves which are suppressed significantly on crossing the spin fluctuation-induced Stoner excitation boundary. In the long wave limit the theory reproduces the self-consistently renormalized spin fluctuation theory of Moriya and Kawabata.

39 citations



Journal ArticleDOI
TL;DR: In this paper, the spin wave excitations in the itinerant antiferromagnetics of γFeMn alloys have been studied by neutron scattering and the results are favorable to the multiple spin density wave state is assumed to exist.
Abstract: The spin wave excitations in the itinerant antiferromagnetics of γFeMn alloys have been studied by neutron scattering. The isotropic dispersion relation has been observed for γFe 0.7 Mn 0.3 and γFe 0.5 Mn 0.5 . The velocities of spin waves at room temperature are 230±30 meVA, 220±30 meVA and 160±30 meVA for Fe 0.7 Mn 0.3 , Fe 0.5 Mn 0.5 and Fe 0.3 Mn 0.7 , respectively. All samples have the spin wave energy gaps of about 10 meV at 0 K which shows a similar temperature dependence. The damping of the spin wave is significant and it depends on the momentum transfer of the spin waves. The magnon-like excitation persists even 200 degrees above the Neel temperature for Fe 0.5 Mn 0.5 . The results are favorable to the itinerant electron model where the multiple spin density wave state is assumed to exist.

35 citations


Journal ArticleDOI
TL;DR: In this article, the Larmor electromagnetic and spin-wave branches of a planar ferromagnetic metal with TEM microwave excitation at normal incidence have been examined to derive physical insight into their dependence on material parameters and orientation, the interaction between branches, and the polarization character associated with the related ecxitations.
Abstract: The properties of the four spin-wave dispersion branches for a planar ferromagnetic metal with TEM microwave excitation at normal incidence have been examined to derive physical insight into (a) their dependence on material parameters and orientation, (b) the interaction between branches, and (c) the polarization character associated with the related ecxitations. The Larmor electromagnetic and spin-wave branches are found to exhibit a peculiar crossover effect at a critical damping value (α ∼ 0·014 for permalloy). The polarizations vary from circular for the static field normal to the surface to elliptical for an in-plane static field. For the in-plane case, the major polarization axes are parallel and perpendicular to the surface for the Larmor and antilarmor branches, respectively. The well known Ament-Rado and Vittoria formulations have also been modified to include the effect of exchange in the damping term of the Landau-Liftshitz equation. The secular determinant is simplified considerably and the form of the dispersion equations is changed significantly. The only large effect on the branches themselves is to increase the attenuating component of the propagation parameterk for large ¦k¦.

34 citations


Journal ArticleDOI
TL;DR: In this article, the authors derived the dynamic correlation functions between a pair of spin operators at any two sites within a semi-infinite Heisenberg ferromagnet at low temperatures, T<
Abstract: Results are derived for the dynamic correlation functions between a pair of spin operators at any two sites within a semi-infinite Heisenberg ferromagnet at low temperatures, T<

Journal ArticleDOI
TL;DR: In this paper, the authors extended the discussion of Kawabata's method to include both longitudinal and transverse spin fluctuations, and found that it is internally consistent and somewhat less ad hoc than it appeared in its original presentation.
Abstract: The low-frequency long-wavelength spin fluctuation modes make a major contribution to the free energy near the ferromagnetic instability of an itinerant-electron model. These fluctuations renormalize the static spin susceptibility and depress the transition temperature predicted by Stoner theory. Moriya and Kawabata (MK) have suggested a simple way of computing the depression self-consistently, by making sure the spin fluctuations go soft at the renormalized temperature ${T}_{c}$ rather than at the Stoner value. We extend the discussion of MK to include both longitudinal and transverse spin fluctuations, and find a ${T}_{c}$ which is only slightly smaller than ${T}_{c}^{\mathrm{MK}}$. We also discuss the relation between ${T}_{c}$ determined from the condition that the paramagnons go soft and that obtained by considering the softening of the spin waves. We argue that our new results give evidence that the basic MK procedure is internally consistent and somewhat less ad hoc than it appeared in its original presentation.

Journal ArticleDOI
TL;DR: In this paper, an improved version of the Caroli-Blandin (1966) form of the effective interaction between local magnetic moments in metals is discussed, which is shown to explain some aspects of the magnetic properties of the Heusler alloy Pd2MnSn and the dilute magnetic alloys CuFe and CuMn.
Abstract: For pt.I see ibid., vol.6, p.233 (1976). An improved version of the Caroli-Blandin (1966) form of the effective interaction between local magnetic moments in metals is discussed. It is shown to explain some aspects of the magnetic properties of the Heusler alloy Pd2MnSn and the dilute magnetic alloys CuFe and CuMn. In this context the ordered alloy Cu3Mn is also discussed.

Journal ArticleDOI
TL;DR: In this article, an expression for the spin wave stiffness coefficient was obtained within the local exchange approximation for nickel and the formula was evaluated for nickel using wave functions and energies obtained from a band calculation.

Journal ArticleDOI
TL;DR: In this paper, the coherent potential approximation (CPA) and the random phase approximation (RPA) were extended to the case of NiFe alloys and it was shown that D is very sensitive to the assumed exchange splitting in pure nickel and that within the RPA reasonable agreement with experiment is obtained only by assuming an unusually large value for this parameter.
Abstract: Previous numerical calculations for a model of nickel alloys, employing the coherent potential approximation (CPA) and the random phase approximation (RPA), are extended to iron alloys. It is shown that often the effective scattering potentials are sufficiently weak for a rigid band calculation of the spin wave stiffness constant D to be a good guide to the more elaborate CPA calculations. The case of NiFe alloys is re-examined in the light of a recent calculation by Riedinger and Nauciel-Bloch (ibid., vol.5, p.732 (1975)). It is shown that D is very sensitive to the assumed exchange splitting in pure nickel and that within the RPA reasonable agreement with experiment is obtained only by assuming an unusually large value for this parameter.

Journal ArticleDOI
TL;DR: In this article, the collective modes of the Balian- Werthamer state in the collisionless limit were studied and the effect of the dipolar interaction on these modes was discussed.
Abstract: Making use of a model Hamiltonian, which includes, besides the kinetic energy and the BCS-like pairing energy, the spin exchange energy as well as the dipolar interaction energy, we study theoretically the collective modes of the Balian - Werthamer state in the collisionless limit. In the absence of the dipolar interaction energy, the collective modes are classified according to their total angular momentumJ. Among 18 distinct modes, one mode withJ=0 and three modes withJ=1 are gapless. The latter modes couple with the spin fluctuation and are identified with spin wave modes. The effect of the dipolar interaction on these modes is discussed.

Journal ArticleDOI
TL;DR: In this paper, the character of spatial and spectral spin diffusion processes in disordered spin systems is studied based on averaging of the rate equations, valid for fixed spin positions, over different particle configurations.
Abstract: The character of spatial and spectral spin diffusion Processes in disordered spin systems is studied. The analysis is based on averaging of the rate equations, valid for fixed spin positions, over different particle configurations. New Expressions for the spatial and spectral diffusion constants are derived and compared with earlier theories. [Russian Text Ignored].

Journal ArticleDOI
TL;DR: In this paper, the authors interpret the spin-wave lineshape in the two-dimensional ferromagnet K2CuF4 by a theory developed for small wavelengths, as is relevant for inelastic neutron scattering, applicable for temperatures both above and below the Curie temperature.
Abstract: The authors interpret the spin-wave lineshape in the two-dimensional ferromagnet K2CuF4 by a theory developed for small wavelengths, as is relevant for inelastic neutron scattering, applicable for temperatures both above and below the Curie temperature. The agreement between theory and experimental results is rather good. However, at high temperatures, when the spin-wave lineshape is very broad, the present theory, which is available for energies near the spin-wave energy omega q, gives only qualitative results.

Journal ArticleDOI
TL;DR: In this paper, the spin wave interaction plays a rather important role in the nearly two-dimensional magnetic system and gives rise to a logarithmic term in the expansion of the magnetization with respect to the temperature.
Abstract: The temperature and the magnetic field dependences of the magnetization of the ferromagnetic layer-type compound K 2 CuF 4 have been analyzed by the spin wave theory which takes into account the spin wave interaction. It is shown that the spin wave interaction plays rather important role in the nearly two-dimensional magnetic system and gives rise to a logarithmic term in the expansion of the magnetization with respect to the temperature. The apparent T 3/2 temperature dependence of the magnetization can be shown to be realized in a certain temperature region. With the use of the exchange interaction constants estimated in the previous investigations, the present calculation shows excellent agreements with the experiments.

Journal ArticleDOI
TL;DR: The spin wave dispersion relation in an Invar alloy Fe0.65Ni0.35 has been measured at 4.2 K in the direction by neutron inelastic scattering as mentioned in this paper.

Journal ArticleDOI
TL;DR: In this paper, the effect of conductivity on the spin-wave spectrum of thin Permalloy ferromagnetic films has been investigated and it is known that the calculated mode locations and amplitudes are in excellent agreement with some experimental data in the range 800-2700 A in thickness.
Abstract: The effect of conductivity on the spin‐wave spectrum of thin Permalloy ferromagnetic films has been investigated. If conductivity effects are included and a simple surface anisotropy is assumed, it is known that the calculated mode locations and amplitudes for Permalloy films are in excellent agreement with some experimental data in the range 800–2700 A in thickness. If conductivity effects are omitted, a much simpler calculation is possible, but the error in mode location and amplitude has been unknown. For both perpendicular and parallel resonance geometries, detailed calculations reported here have shown that mode locations are not significantly affected over the above thickness range, and that the main mode amplitude is in error by only 20% at 800 A thickness. However, for 2000 A thickness, the main mode amplitude is in error by a factor of 2.5.

Journal ArticleDOI
TL;DR: In this article, a molecular-field calculation of the magnetic configurations in Er is found to reproduce the neutron diffraction results of the three different magnetic phases and to give a reasonable fit to the magnetization data at 4.2K.
Abstract: A molecular-field calculation of the magnetic configurations in Er is found to reproduce the neutron diffraction results of the three different magnetic phases and to give a reasonable fit to the magnetization data at 4.2K. The two-ion coupling is considered to be described by the inter-planar coupling parameters deduced from the dispersion of the spin waves in the low temperature conical phases. The four (effective) crystal-field parameters are determined by the fit to the experimental data. Projecting the magnetic moments present in the intermediate phase of Er (18-52.4K) to a common origin the calculations indicate that the hodograph of the moments is very close to an ellipse that has its major axis parallel to the c-axis.

Journal ArticleDOI
TL;DR: The spin-wave dispersion relations for Rb2CrCl4, which orders ferromagnetically at 63K have been measured at 4.5K in this article, and the spinwave energies confirm the two-dimensional nature of the interactions; writing H12=-2J12S1.S2 they can be fitted by a single exchange parameter J1=0.66+or-0.1K.
Abstract: The spin-wave dispersion relations for Rb2CrCl4, which orders ferromagnetically at 63K have been measured at 4.5K. The spin-wave energies confirm the two-dimensional nature of the interactions; writing H12=-2J12S1.S2 they can be fitted by a single exchange parameter J1=0.66+or-0.01 meV (7.7+or-0.1K) representing the interaction between nearest-neighbour in-plane ions. Rb2CrCl4 should therefore typify a two-dimensional, S=2, easy-plane ferromagnet.

Journal ArticleDOI
TL;DR: The linearized hydrodynamic theory of 3He-B is derived from thermodynamics by symmetry arguments alone as mentioned in this paper, and spin waves are obtained as Goldstone modes of the broken spin-orbit symmetry.
Abstract: The linearized hydrodynamic theory of 3He-B is derived from thermodynamics by symmetry arguments alone. Spin waves are obtained as Goldstone modes of the broken spin-orbit symmetry. Their spectrum omega (k) is analysed and found to be isotropic, phonon-like with a damping approximately k2. Effects of the weak magnetic dipole interaction and an applied external magnetic field are calculated. The former leads to a mixing of one transverse mode and the longitudinal mode and a gap in the spectrum of one of the Goldstone modes which is the large longitudinal NMR shift characteristic of 3He-B.

Journal ArticleDOI
TL;DR: In this article, a far infrared investigation of antiferromagnetic resonance by means of Fourier transform spectroscopy has been carried out in FeCl2, FeBr2 and FeI2.
Abstract: A far infrared investigation of antiferromagnetic resonance by means of Fourier-transform spectroscopy has been carried out in FeCl2, FeBr2 and FeI2. In FeCl2 and FeBr2 our results are found to agree well with the two-sublattice model with an anisotropy parameter D = 9.6 K. In FeI2 three absorption peaks situated at 21.6 cm-1, 29.2 cm-1, and 32.2 cm-1 have been attributed to excitation of zone-center spin waves, which can be understood only by assuming that FeI 2 has more than two sublattices. The AFMR frequencies in a simple four sublattice model have been calculated, and the parameters relevant to FeI 2 have been deduced. However the observation of a 3 cm-1 splitting between the two higher modes suggests that such a model may be too simple.

Journal ArticleDOI
TL;DR: In this paper, a previous approach to spin dynamics in the non-linear regime was generalized to the nonlinear regime, where the direction of the order parameter has large deviations from its equilibrium position.
Abstract: A previous approach to spin dynamics in superfluid $^{3}\mathrm{He}$ is generalized to the nonlinear regime, where the direction of the order parameter has large deviations from its equilibrium position. The results are used to study the hydrodynamic regime, to derive an equation for the nonlinear regime in the ringing experiments, and to consider the nonlinear effects arising in spin-echo experiments for small tipping angles. The results for the NMR linewidths (in the linear regime) are compared with a very recent work of Leggett and Takagi. Finally, the behavior of these linewidths is investigated at low temperature, where the hydrodynamic assumption $\ensuremath{\omega}\ensuremath{\tau}\ensuremath{\ll}1$ is no longer valid.

Journal ArticleDOI
TL;DR: In this paper, a microscopic model for the surface parameter in thin YIG films is proposed to explain the observed properties of the non-propagating surface spin-wave, and excellent agreement is observed between the experimental results and the prediction of the microscopic theory.

Journal ArticleDOI
TL;DR: In this paper, the problem of spin wave propagation in itinerant ferromagnets and antiferromagnetic devices is discussed from the band-theory point of view, and the agreement between the result and the experiment is as good as or better than the existing theories.
Abstract: The problem of spin waves in itinerant ferromagnets and antiferromagnets is discussed from the band-theory point of view. In the ground state, the energy bands are spin split and there is a spin-density cloud around each ion site. When a spin wave is excited, we postulate that the spin cloud of each ion precesses as a rigid unit, i.e., a quasispin. This gives rise to a modulation of the effective exchange potential, and the difference between the modulated potential and the ground-state exchange potential has the form of the $s\ensuremath{-}d$ interaction. Here the $s$ part includes all the conduction electrons and the $d$ part arises from the precession of the quasispins. The magnon energy, electron band splitting, and the magnon-magnon interaction are discussed. In every case the agreement between the result and the experiment is as good as or better than the existing theories.

Journal ArticleDOI
TL;DR: In this paper, the effects of the biquadratic exchange interaction on the temperature dependence of the magnetic specific heat and sublattice magnetization have been calculated with the use of the spin wave theory for linear chain antiferromagnet.
Abstract: The effects of the biquabratic exchange interaction on the temperature dependence of the magnetic specific heat and sublattice magnetization have been calculated with the use of the spin wave theory for linear chain antiferromagnet. The antiferromagnetic spin structure changes abruptly and begins to make a cant at a certain ratio P c of the biquadratic exchange interaction to the Heisenberg one, which is reasonably small enough to appear in the real antiferromagnet with large spin. This change of the spin structure is shown to give significant effects on the magnetic properties.

Journal ArticleDOI
TL;DR: In this paper, a T 3 2 contribution to both the heat capacity and the saturation magnetization of the weakly ferromagnetic compound UPt reveals the existence of spin waves in the Ferromagnetic state below the Curie temperature of 30 K. The entropy of ordering, extracted from calorimetric data on UPt and the isostructural nonmagnetic compound ThPt, is much smaller than the degeneracy entropy expected from the p ss″ e 5f3 (U3+) or 5f2(U4+) ionic configuration.