Showing papers on "Magnon published in 1985"
TL;DR: In this article, the authors extended the theory of two-magnon scattering to disordered ferromagnetic metals and derived the formula for the rf susceptibility in the parallel (in plane) configuration by using the retarded Green's function formalism.
Abstract: The theory of two‐magnon scattering is extended to disordered ferromagnetic metals. In order to treat properly the role of two‐magnon scattering in metals we have derived the formula for the rf susceptibility in the parallel (in plane) configuration by using the retarded Green’s function formalism. The roles of the elliptical polarization, the finite values of resonance k vectors, nonresonant spin‐wave interactions, eddycurrent effects as well as the contribution of spin‐orbit interaction to the intrinsic damping are included. We have evaluated the susceptibility in the presence of magnetostatic inhomogeneities, statistical variations of local properties and fluctuating exchange interactions.
182 citations
TL;DR: In this article, a self-energy correction term due to the scattering with magnon-like modes is calculated, and shown to have a part representing the relaxation process through the c-f hybridization.
34 citations
TL;DR: In this article, the thermoelectric power of magnetic (cubic) metals taking into account the inelastic scattering of electrons by phonons and by localized spins was investigated.
34 citations
TL;DR: In this article, the spin reorientation transition in superlattices fabricated from a ferromagnetic and an antiferromagnetic component is studied. But the authors focus on the case where the anitferromagnetic constituent contains an even number of spin sheets, and the spin flop field can be very much lower than that realized in the isolated antiferron.
Abstract: Superlattice structures may exhibit unique properties, distinctly different from those of the individual constituents from which the structure is synthesized. We illustrate this by exploring some properties of model superlattices fabricated from a ferromagnet and an antiferromagnet, the latter with sheets of ferromagnetically aligned spins each parallel to the interface. We find magnetic‐field‐induced spin reorientation transitions in such a structure. These may be viewed as the antiferromagnetic spin flop transition, modified by the presence of the intervening ferromagnetic layers. For the case where the anitferromagnetic constituent contains an even number of spin sheets, the spin flop field can be very much lower than that realized in the isolated antiferromagnet.
33 citations
TL;DR: In this article, the dependence of the magnon frequencies on the magnetic inplane field and on the wave vector was measured for several samples with different numbers and thicknesses of the layers.
Abstract: Spin waves which are characteristic of periodic structures of thin ferromagnetic Co films alternating with nonmagnetic Nb films have been investigated by means of Brillouin light scattering. The dependence of the magnon frequencies on the magnetic inplane field and on the wave-vector was measured for several samples with different numbers and thicknesses of the layers. The experimental data are in good agreement with a theory of magnetostatic surface spin waves in such media elaborated by Grunberg and Mika. The amplitudes of the transverse magnetization in the different layers of the stack have been calculated. The highest frequency branch resembles the Damon-Eshbach surface magnon. With decreasing frequency the branches acquire volume mode character. In addition, a number of phonon branches has been observed which are interpreted as plate modes of the combined Co-Nb layer on the Si substrate.
26 citations
TL;DR: In this article, a theory of the thermoelectric power tensor of anisotropic ferromagnetic metals with localized magnetic moments starting from the Boltzmann equation and incorporating anisotropy effects due to the lattice structure is presented.
22 citations
TL;DR: Inelastic magnetic neutron spectra were taken on polycrystalline YbBe 13 between 1.2 and 300 K as mentioned in this paper, where the formation of a magnon corroborates the existence of a magnetic phase transition observed also by static susceptibility.
18 citations
TL;DR: In this paper, a review of studies of chaotic dynamics in several solid state systems is given, relevant equations of motion are given, and experimental results are presented and interpreted from the relevant equations, including numerical solutions.
Abstract: A review is given of studies of chaotic dynamics in several solid state systems. In each case the physical system is described, relevant equations of motion are given, experimental results are presented and interpreted, more or less, from the relevant equations, including numerical solutions. The systems are: (1) An electron-hole helical plasma density wave in a Ge crystal in parallel electric and magnetic fields; this shows period doubling and quasiperiodic routes to chaos. (2) Standing mode spin wave packets in ferrite spheres, excited by driving ferromagnetic resonance of the uniform mode; this system shows period doubling to chaos and periodic windows. (3) Resonantly driven p-n junctions in Si show extremely nonlinear behavior due to charge stored during injection; one junction shows period doubling to chaos and period adding (frequency locking); coupled junctions show, in addition, quasiperiodicity, entrainment, and behavior generic to coupled nonlinear oscillators. The fractal dimension is measured for these systems.
17 citations
17 citations
TL;DR: In this paper, it was shown that N and S-site spins form a canted state for applied field inclined from the (111) plane, and from this canting angle, they can estimate the biquadratic interaction j 1.
Abstract: From detailed magnetization measurements, it becomes clear in the NNS state of EuSe that N and S-site spins form a canted state for applied field inclined from the (111) plane. From this canting angle, we can estimate the biquadratic interaction j 1 . Transition fields, H 2 and H 3 , together with the paramagnetic Curie temperature, give the values of J 1 , J 2 and J 3 definitely. Using these values, we calculate the anisotropic magnetization process in excellent agreement with experiment. Zero point reductions of magnetization both in NNS and NNN states are observed to be large. Moreover, the field and the temperature dependences of the magnetization in the NNN region are large. Introducing the pseudo-dipole term, we calculate the zero point reduction in the NNN state consistently with the observed one. Softening of the magnon is the origin of the unusual behaviour of the magnetization.
13 citations
Journal Article•
TL;DR: In this article, the spectrum generating algebra (SGA) is used to study the low-lying excitations in various localised-spin models of ferromagnetic, ferrimagnetic and antiferromagnetic solids.
Abstract: The idea of the spectrum generating algebra (SGA) is used to study the low-lying excitations in various localised-spin models of ferromagnetic, ferrimagnetic and antiferromagnetic solids. The noncompact algebra SO(2,1) approximately SU(1,1) is found to generate the spin wave or the magnon spectrum for ferromagnetic, ferrimagnetic and antiferromagnetic Bravais lattices with nearest-neighbour exchange interactions (Heisenberg model). The ferromagnetic case is treated including dipolar interactions in the model. For a quadratic antiferromagnet with easy-plane anisotropy the SGA is found to be the direct product SO(2,1)(X)SO(2,1) approximately SO(2,2). For the XY and the Heisenberg-Ising models of an antiferromagnetic linear chain the SGA is the compact counterpart of SO(2,1), i.e. SO(3) approximately SU(2). It is concluded that if the magnons are quantised as bosons then the SGA is the noncompact algebra SO(2,1), and if they are quantised as fermions then the SGA is the compact angular momentum algebra SO(3).
TL;DR: In this article, the properties of solid oxygen were studied by means of an integrated lattice-dynamics-spin-wave approach which uses the random-phase approximation, based on a Hamiltonian from first principles, which includes the structural dependence of the spin coupling parameters.
Abstract: The properties of solid ${\mathrm{O}}_{2}$ are studied by means of an integrated lattice-dynamics--spin-wave approach which uses the random-phase approximation. This approach is based on a Hamiltonian from first principles, which includes the structural dependence of the spin coupling parameters. The calculated magnon and libron frequencies in \ensuremath{\alpha} oxygen are in satisfactory agreement with experiment and the anomalously large libron splitting at the \ensuremath{\beta}-\ensuremath{\alpha} phase transition is explained.
TL;DR: In this paper, the inelastic neutron scattering due to the magnetic excitations in a single crystal of gamma -Mn90Cu10 has been measured between 1 and 10 THz for six temperatures between 110 and 520K.
Abstract: The inelastic neutron scattering due to the magnetic excitations in a single crystal of gamma -Mn90Cu10 has been measured between 1 and 10 THz for six temperatures between 110 and 520K. The Neel temperature is 465K. Below TN, the scattering is well described by isotropic, heavily damped magnons. At room temperature, the velocity of the magnons is about 44 THz AA and the gap is 2.1 THz. Both values depend on the exact nature of the model used in the analysis. Consistent with theoretical expectation, the damping is wavevector dependent. When the temperature is raised above TN, there is no dramatic change in either the magnon scattering or the fitted parameters. However, above TN, a better description of the scattering at low energies is given by a scattering cross section derived from fluctuations, whereas this description breaks down at higher energy. Conversely, the magnon description is better at high energies but produces inconsistent parameters at lower energies. The change from fluctuation- to magnon-like behaviour occurs at k=0.12 AA-1 at 470K (1.011TN) and at 0.19 AA-1 at 549K (1.116TN). These wavevectors are interpreted as a measure of the size of the regions of fluctuating but correlated spins that can sustain magnons above TN.
TL;DR: In this paper, high-resolution neutron scattering studies have been made of the long wavelength spin excitations in a ribbon sample of amorphous Fe0.86B0.14, which exhibits Invar properties.
Abstract: High‐resolution neutron scattering studies have been made of the long wavelength spin excitations in a ribbon sample of amorphous Fe0.86B0.14, which exhibits Invar properties. Spin waves were observed in the wave vector range 0.05 A−1≤q≤0.12 A−1 at temperatures between 300 K (0.54 Tc) and 500 K (0.90 Tc). The spin wave energies are well described by a dispersion relation E=Dq2+Δ. The small energy gap Δ of ≊0.04 meV is attributed primarily to the dipole‐dipole interaction. The stiffness constant renormalizes with temperature as D=D(0)[1.0−0.86 (T/Tc) 5/2] in the range of temperatures under study, with D(0)=132 meV A2. This value of D(0) is approximately twice as large as that calculated from the T3/2 coefficient of the magnetization, a discrepancy common to many Invar materials. Plots of the intrinsic linewidths against q4 and T2 reveal that the data are consistent with the Γ∝q4[Tln(kT/E)]2 dependence predicted for a Heisenberg ferromagnet. There are no anomalies in the spin‐wave lifetimes at long waveleng...
TL;DR: In this article, the peculiarities of the density of states near the Fermi energy of the degenerate ferromagnetic semiconductor (FMS) due to the electron-magnon interaction are considered.
TL;DR: In this paper, the magnon softening due to near cancellation of exchange interactions, J 1 + J 2 ≈ 0, and thus enhanced effects of J 3 and the biquadratic interaction j 1 were determined unambiguously.
TL;DR: In this paper, the magnitudinal and directional dispersion of magnon-polaritons in uniaxial antiferromagnetic crystals is studied and a proof is given for the existence of a purely longitudinal magnon propagating perpendicular to the optic axis.
TL;DR: In this paper, the density of states of magnon-like excitations of Eu x Sr 1−x S spin glasses with x=0.25, 0.44 and 0.54 was calculated for very strong magnetic fields B, i.e. B>3 T. The results agree quantitatively with recent experiments, for T between 0.3 K and 5 K (10 K) in magnetic fields of 3.6 T (6.6
Abstract: The density of states of magnon-like excitations of Eu x Sr 1−x S spin glasses with x=0.25, 0.44 and 0.54 is calculated for very strong magnetic fields B, i.e. B>3 T. It is found that for these high fields the magnon-like excitations can be treated as non-interacting bosons up to temperatures far beyond the spin glass freezing temperature at B=0. From the density of states the magnetic part C H of the specific heat is calculated, without any fit-parameter. The results agree quantitatively with recent experiments, for T between 0.3 K and 5 K (10 K) in magnetic fields of 3.6 T (6.6 T) Etude des excitations de quasi-magnons dans ces composes pour x=0,25, 0,44 et 0,54 en champ magnetique intense (B>3 T). Traitement de ces quasi-magnons comme des bosons non interagissants bien au-dessous de la temperature de transition de verre de spin a B=0. Calcul, sans parametre ajustable, de la densite d'etats des magnons et de la chaleur massique magnetique
TL;DR: In this article, the integrated intensity of the luminescence is measured as a function of temperature and discussed in terms of a three-level model in which the energy transfer from an intrinsic exciton to impurity-induced levels plays an important role.
Abstract: Strong luminescence observed at a low temperature in the antiferromagnetic MnCO3 disappears near the phase transition temperature. It is interpreted as the emission composed of multimagnon and multi‐magnon‐phonon sidebands associated with a pure electronic transition between 6A1g and 4T1g states of manganese ions. Polarization experiments of the fine structure in this red emission reveal that two kinds of radiative traps participate in the transitions. The integrated intensity of the luminescence is measured as a function of temperature and discussed in terms of a three‐level model in which the energy transfer from an intrinsic exciton to impurity‐induced levels plays an important role.Strong luminescence observed at a low temperature in the antiferromagnetic MnCO3 disappears near the phase transition temperature. It is interpreted as the emission composed of multimagnon and multi‐magnon‐phonon sidebands associated with a pure electronic transition between 6A1g and 4T1g states of manganese ions. Polarization experiments of the fine structure in this red emission reveal that two kinds of radiative traps participate in the transitions. The integrated intensity of the luminescence is measured as a function of temperature and discussed in terms of a three‐level model in which the energy transfer from an intrinsic exciton to impurity‐induced levels plays an important role.
TL;DR: The properties of the hot-magnon sideband are explained by the exciton creation accompanied by the annihilation of a thermally excited magnon at the Brillouin-zone edge, and may be understood by the reduction of spin fluctuations in a magnetic field applied in the easy plane of magnetization.
Abstract: Absorption spectra associated with the lowest-energy region of the spin-forbidden transition $^{3}\mathrm{A}_{2\mathrm{g}}$\ensuremath{\rightarrow}${\mathrm{}}^{1}$${\mathrm{T}}_{2\mathrm{g}}^{\mathrm{a}}$ in ${\mathrm{CsNiF}}_{3}$ are investigated in the one-dimensional ferromagnetic phase in magnetic fields up to 4.5 T. Pure-exciton bands are found to have a linear blue shift with a field applied in the easy plane, whereas the hot-magnon band shifts slightly to lower energies. When the field is increased the intensity of the exciton bands increases and the absorption due to the hot-magnon band decreases. An anomalous behavior of the band intensities and the half-widths is observed in fields below 1 T. The structure of the exciton spectra and their field dependence are discussed by using an energy-level scheme obtained by a single-ion approximation. The properties of the hot-magnon sideband are explained by the exciton creation accompanied by the annihilation of a thermally excited magnon at the Brillouin-zone edge. The anomalies of the exciton and the hot-magnon bands observed in low fields may be understood by the reduction of spin fluctuations in a magnetic field applied in the easy plane of magnetization.
TL;DR: Inelastic neutron scattering measurements have been performed on monocrystalline samples of antiferromagnetic iron monoxide (Fe1-xO) for several compositions (x=0.056, 0.070 and 0.072) in order to find with precision the stoichiometry dependence of the spin dynamics.
Abstract: Inelastic neutron scattering measurements have been performed on monocrystalline samples of antiferromagnetic iron monoxide (Fe1-xO) for several compositions (x=0.056, 0.070 and 0.072). The magnetic excitations up to 8 THz have been investigated in order to find with precision the stoichiometry dependence of the spin dynamics. The experimental results have been analysed using a Green function formalism taking into account the spin-orbit interaction, the magnetoelastic coupling and the exchange interactions extending to the second neighbours. The main effect of the stoichiometry on the spin wave branch and the first excited level is a broadening of the magnon lineshapes. Nevertheless, in the case of x=0.056, several peculiar excitations have been found which are probably related to the defect structure and long-range ordering. This ordering has been corroborated by the observation of elastic scattering corresponding to a modulated magnetic and nuclear structure.
TL;DR: CeMg as mentioned in this paper presents somoe characteristics of a Kondo lattice and magnetic excitations have been followed through the whole Brillouin zone, which allow to determine the interactions.
Abstract: CeMg presents somoe characteristics of a Kondo lattice. Magnetic excitations have been followed through the whole Brillouin zone, which allow to determine the interactions.
Journal Article•
TL;DR: In this article, the static and dynamic manifestations of magnetoelastic coupling in the noncollinear antiferromagnet UO2 are investigated theoretically, and it is shown that only optical magnons interact effectively with sound, whereas all three acoustic magnon modes are weakly coupled to the elastic subsystem.
Abstract: The static and dynamic manifestations of magnetoelastic coupling in the noncollinear antiferromagnet UO2 are investigated theoretically. It is shown that only optical magnons interact effectively with sound, whereas all three acoustic magnon modes are weakly coupled to the elastic subsystem. The existence of a linear piezomagnetic effect in this compound is predicted. A method of calculating the magnon spectrum in the vicinity of symmetric Brillouin-zone points is demonstrated. The method takes full account of the crystallographic and magnetic symmetry of the system.
TL;DR: In this paper, the spectrum of elementary excitations arising in processes of desintegration of magnon drops in one-dimensional ferromagnetic structures is investigated and a new method of solving the gap equation is used.
Abstract: The spectrum of elementary excitations arising in processes of desintegration of magnon drops in one-dimensional ferromagnetic structures is investigated. A new method of solving the gap equation is used. It is shown that those elementary excitations are gapless. This result is in accordance with Goldstone's theorem. It was also shown that these elementary excitations do not lead to the superfluidity effect.
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TL;DR: In this article, the authors observed a huge contribution of magnons to the heat current in (TMTSF)2X (X=C1 04, PF6) below the antiferromagnetic transition.
Abstract: We have observed a huge contribution of magnons to the heat current in (TMTSF)2X (X=C1 04, PF6) below the antiferromagnetic transition. The results are discussed in connection with other physical properties related to these compounds.
TL;DR: In this paper, the dominant orbital character of each corresponding excited state was unambiguously established via polarized absorption and magnetic circular dichroism (MCD) measurements, and the influence of the tetragonal distortion and spin-orbit coupling on all orbital triplets was determined experimentally, the results being in fair agreement with theoretical predictions.
Abstract: Electric dipole origins were observed for all multiplets except 4 T 2 (G) in the 17000-31000 cm −1 spectral range. The dominant orbital character of each corresponding excited state was unambiguously established via polarized absorption and magnetic circular dichroism (MCD) measurements. The influence of the tetragonal distortion and spin-orbit coupling on all orbital triplets was determined experimentally, the results being in fair agreement with our theoretical predictions. Magnon sidebands were always observed with the predicted polarization. The zone-edge magnon frequency was found to be 90 cm −1 , exciton-magnon interaction being negligible Observation des raies excitoniques dipolaires electriques pour tous les multiplets a l'exception de 4 T 2 (G) entre 17000 et 31000 cm −1 . Caracterisation de la fonction d'onde des etats excites a l'aide de mesure d'absorption en lumiere polarisee et de dichroisme circulaire magnetique