Showing papers on "Spin wave published in 1978"

Introduction to solid-state theory

Abstract: 1. Fundamentals.- 1.1 Introduction.- 1.2 The Basic Hamiltonian.- 1.3 The Hartree-Fock Approximation.- 2. The One-Electron Approximation.- 2.1 The Electron Gas Without Interaction.- 2.1.1 Introduction.- 2.1.2 The Energy States.- 2.1.3 Excited States.- 2.1.4 The Fermi Distribution.- 2.1.5 Free Electrons in an Electric Field.- 2.1.6 Free Electrons in a Magnetic Field.- 2.1.7 Dia- and Paramagnetism of Free Electrons, the de Haasvan Alphen Effect.- 2.2 Electrons in a Periodic Potential.- 2.2.1 Introduction.- 2.2.2 The Symmetries of the Crystal Lattice.- 2.2.3 The Schrodinger Equation for Electrons in a Periodic Potential.- 2.2.4 The Reciprocal Lattice, Bragg Reflections.- 2.2.5 Consequences of Translational Invariance.- 2.2.6 Nearly Free Electron Approximation.- 2.2.7 Wannier Functions, LCAO Approximation.- 2.2.8 General Properties of the Function En(k).- 2.2.9 Dynamics of Crystal Electrons.- 2.2.10 The Density of States in the Band Model.- 2.2.11 The Band Structure of Metals, Fermi Surfaces.- 2.2.12 The Band Structure of Semiconductors and Insulators.- 2.2.13 Consequences of the Invariance of the Hamiltonian to Symmetry Operations of the Space Group.- 2.2.14 Irreducible Representations of Space Groups.- 2.2.15 Spin, Time Reversal.- 2.2.16 Pseudopotentials.- 3. Elementary Excitations.- 3.1 The Interacting Electron Gas: Quasi-Electrons and Plasmons.- 3.1.1 Introduction.- 3.1.2 The Coulomb Interaction.- 3.1.3 The Hartree-Fock Approximation for the Electron Gas.- 3.1.4 Screening, Plasmons.- 3.1.5 Quasi-Electrons.- 3.1.6 The Dielectric Constant of the Electron Gas.- 3.2 Electron-Hole Interaction in Semiconductors and Insulators: Excitons.- 3.2.1 Introduction.- 3.2.2 The Ground State of the Insulator in Bloch and Wannier Representation.- 3.2.3 Excited States, the Exciton Representation.- 3.2.4 Wannier Excitons.- 3.2.5 Frenkel Excitons.- 3.2.6 Excitons as Elementary Excitations.- 3.3 Ion-Ion Interaction: Phonons.- 3.3.1 Introduction.- 3.3.2 The Classical Equations of Motion.- 3.3.3 Normal Coordinates, Phonons.- 3.3.4 The Energy Content of the Lattice Vibrations, Specific Heat.- 3.3.5 Calculation of Phonon Dispersion Relations.- 3.3.6 The Density of States.- 3.3.7 The Long Wavelength Limit: Acoustic Branch.- 3.3.8 The Long Wavelength Limit: Optical Branch.- 3.4 Spin-Spin Interaction: Magnons.- 3.4.1 Introduction.- 3.4.2 Spin Waves in Ferromagnets: Magnons.- 3.4.3 Spin Waves in Lattices with a Basis, Ferri-, and Antiferromagnetism.- 3.4.4 Ferromagnetism Near the Curie Temperature.- 3.4.5 Ordered Magnetism of Valence and Conduction Electrons, the Collective Electron Model.- 4. Electron-Phonon Interaction: Transport Phenomena.- 4.1 The Interaction Processes.- 4.1.1 Introduction.- 4.1.2 Interaction of Electrons with Acoustic Phonons.- 4.1.3 Electron-Phonon Interaction in Polar Solids, Polarons.- 4.2 The Boltzmann Equation.- 4.2.1 Introduction.- 4.2 Boltzmann Equations for the Electron and Phonon Systems.- 4.2.3 The Relaxation Time Approximation.- 4.2.4 The Variational Method.- 4.3 Formal Transport Theory.- 4.3.1 The Transport Equations.- 4.3.2 Transport Coefficients Without a Magnetic Field.- 4.3.3 Transport Coefficients with a Magnetic Field.- 4.4 Transport in Metals and Semiconductors.- 4.4.1 The Electrical Conductivity.- 4.4.2 Transport Coefficients in the Relaxation Time Approximation.- 4.4.3 Limits of Validity and Possible Extensions of the Approximations Used.- 5. Electron-Electron Interaction by Exchange of Virtual Phonons: Superconductivity.- 5.1 Introduction.- 5.2 Cooper Pairs.- 5.3 The Ground State of the Superconducting Electron Gas.- 5.4 Excited States.- 5.5 Comparison with Experiment.- 5.6 Thc Meissner-Ochsenfeld Effect.- 5.7 Further Theoretical Concepts.- 6. Interaction with Photons: Optics.- 6.1 Fundamentals.- 6.1.1 Introduction.- 6.1.2 Photons.- 6.1.3 Polaritons.- 6.1.4 The Complex Dielectric Constant.- 6.2 Electron-Photon Interaction.- 6.2.1 Introduction.- 6.2.2 Direct Transitions.- 6.2.3 Indirect Transitions.- 6.2.4 Two-Photon Absorption.- 6.2.5 Exciton Absorption.- 6.2.6 Comparison with Experimental Absorption and Reflection Spectra.- 6.2.7 Absorption by Free Charge Carriers.- 6.2.8 Absorption and Reflection in a Magnetic Field.- 6.2.9 Magneto-Optics of Free Charge Carriers.- 6.3 Phonon-Photon Interaction.- 6.3.1 Introduction.- 6.3.2 One-Phonon Absorption.- 6.3.3 Multi-Phonon Absorption.- 6.3.4 Raman and Brillouin Scattering.- 7. Phonon-Phonon Interaction: Thermal Properties.- 7.1 Introduction.- 7.2 Frequency Shift and Lifetime of Phonons.- 7.3 The Anharmonic Contributions to the Free Energy, Thermal Expansion.- 7.4 The Thermal Conductivity of the Lattice.- 8. Local Description of Solid-State Properties.- 8.1 Localized and Extended States.- 8.2 The Chemical Bond.- 8.2.1 Introduction.- 8.2.2 The Localized Single Bond.- 8.2.3 Localized and Delocalized Bonds.- 8.2.4 Solids with Localized Bonds: Insulators and Semiconductors.- 8.2.5 The Dielectric Theory of the Covalent Bond.- 8.2.6 Solids with Delocalized Bonds: Metals.- 8.3 Local Versus Nonlocal Description in Unperturbed Lattices.- 8.3.1 Introduction.- 8.3.2 Correlations, the Hubbard Model.- 8.3.3 Metal-Insulator Transitions.- 8.3.4 Limits of the Boltzmann Equation, the Kubo and Kubo-Greenwood Formulae.- 8.3.5 The Small Polaron.- 8.3.6 Hopping Conductivity in Polar Solids.- 9. Localized States.- 9.1 Point Imperfections.- 9.1.1 Introduction.- 9.1.2 Description Within the Framework of the Band Model.- 9.1.3 Crystal Field Theory.- 9.1.4 Localized Lattice Vibrations.- 9.1.5 Defect Statistics, Reaction Kinetics.- 9.1.6 Disorder Equilibria.- 9.1.7 Diffusion and Ionic Conduction.- 9.1.8 Recombination Processes at Imperfections.- 9.1.9 Optical Transitions at Imperfections, Configuration Coordinates.- 9.1.10 Electron-Phonon Interaction at Imperfections.- 9.1.11 Bound Excitons.- 9.1.12 Imperfections as Scattering Centres, the Kondo Effect.- 9.2 Localized States and Elementary Excitations at Surfaces.- 9.2.1 Introduction.- 9.2.2 Electronic Surface States.- 9.2.3 Surface-Phonons, -Polaritons, and -Plasmons.- 10. Disorder.- 10.1 Localized States in Disordered Lattices.- 10.1.1 Introduction.- 10.1.2 Localized States.- 10.1.3 Density of States.- 10.2 Transport in Disordered Lattices.- 10.2.1 Transport in Extended States.- 10.2 The Hopping Probability.- 10.2.3 Fixed Range and Variable Range Hopping.- 10.2.4 Conductivity in Impurity Bands and in Amorphous Semiconductors.- Appendix: The Occupation Number Representation.- Problems to Chapters 1-9.

Phase Transitions in Quantum Spin Systems with Isotropic and Nonisotropic Interactions

Abstract: We prove the existence of spontaneous magnetization at sufficiently low temperature, and hence of a phase transition, in a variety of quantum spin systems in three or more dimensions. The isotropic spin 1/2 x−y model and the Heisenberg antiferromagnet with spin 1, 3/2,...and with nearest neighbor interactions on a simple cubic lattice are included.

Specific heat of concentrated kondo systems: (La, Ce)Al2 and CeAl2

Abstract: We report on specific heat measurements of (La1−x Ce x )Al2 samples, with 1.5 a/o≦x≦100 a/o, performed in magnetic fields of up to 5 T between 0.3 and 10 K. In the Ce rich alloys, and especially in CeAl2, aλ-type peak of an antiferromagnetic phase transition, and at lower temperatures spin waves and very large electronic contributions are clearly visible. In higher magnetic fields, that is when antiferromagnetic order can be suppressed, the specific heat of the alloys exhibits a broadened Schottky peak. All these phenomena add up tok ln 2, i.e. to the correct entropy change per single Ce3+ ion in itsΓ 7 crystal field ground state. We interpret experimental results as an interplay between cooperative magnetism and the single-ion Kondo effect which describes a gradual turning off of one magnetic moment. The broadening of the Schottky peak is directly related to the Kondo temperatureT K , which we determine with a simple “resonance level model”.T K increases by an order of magnitude whenx increases from 1.5 a/o to 100 a/o. This is interpreted as caused by a lattice contraction. A quadraticx dependence of the Neel temperature suggests that (forT≲T K ) stable Ce moments can only exist through pair interactions. The very large (and almost field independent) specific heat term linear in temperature with a coefficientγ=135 mJ/K2 mole for CeAl2 is attributed to the Kondo effect—still present in the antiferromagnetically ordered state. Our evaluation of the experimental data is backed by a molecular field theory for a simplified antiferromagnetic structure combined with the simplest possible Kondo theory.

Surface response of exchange- and dipolar-coupled ferromagnets: Application to light scattering from magnetic surfaces

Abstract: We present the theory of the surface response of a semi-infinite ferromagnet in the presence of both exchange and dipolar coupling, within a continuum theory. The results are applied to a detailed study of the spectral density of surface spin fluctuations. From this we analyze the influence of exchange coupling and surface spin pinning on the frequency, linewidth, and line shape of the Damon-Eshbach surface spin wave, for a number of propagation angles, and for wavelengths sufficiently short that the exchange contribution to the energy of the wave is comparable to the Zeeman and dipolar energies. We also develop the theory of Brillouin scattering from spin waves near magnetic surfaces, and calculate the spectum of scattered light for experimentally interesting geometries, with recent light scattering studies of ferromagnetic surfaces in mind.

Spin wave excitations in a two-dimensional Ising-like antiferromagnet, Rb2CoF4

Abstract: Using inelastic-neutron scattering techniques, the spin wave energy dispersion relation has been investigated at three temperatures in a two-dimensional Ising-like antiferromagnet, Rb2CoF4. The results show there is relatively little dispersion across the Brillouin zone with a very large energy gap at zero wavevector. As the temperature is increased to just below TN there is relatively little renormalisation of the spin waves over the region of wavevectors examined.

Spin Wave Excitations and the Magnetization Curve of Amorphous Ferromagnets

Abstract: Within the Heisenberg model it is studied, how the magnetic excitations and the magnetization curve of an amorphous ferromagnet depend on the exchange integralJ(r). For the “relaxed” structural model of L. von Heimendahl, consisting ofN=888 sites, the density of spin wave states is calculated by means of a continued fraction algorithm, using various model assumptions on the radial dependence ofJ(r). Although it is assumed thatJ(r) is different from zero only within the “nearest neighbour region” of the radial distributiong(r), the density of spin wave states and the critical temperature are strongly influenced by a positive or negative derivative ofJ(r) in this region. However, the magnetization curves, which are calculated in the Tyablikov decoupling approximation fors=1/2, show only a weak flattening, compared with the idealfcc case, when presented overT/Tc. The calculated low-temperature behaviour of the magnetization is compared with recent experiments on ferromagnetic metglasses, and it is found that a description with localized spins and a short-range Heisenberg interaction should be much better for these systems than for the corresponding crystalline metals.

Antiferromagnetic Resonance in TMMC below 1 K

Abstract: Antiferromagnetic resonance in a linear chain antiferromagnet (CH 3 ) 4 NMnCl 3 was observed below 1 K. The experimental results support a spin structure model of the easy plane type in the c -plane. However, the spin configuration in the plane is not determined, and the observed three resonance lines are difficult to explain satisfactorily. The zero field spin wave energy was estimated to be about 0.8 cm -1 . A temperature dependent shift of the resonance point is found at low temperatures, and it was attributed to the nuclear hyperfine anisotropy shift.

Spin waves in the heavy-rare-earth metals Gd, Tb, Dy, and Er

Abstract: The transverse-spin-wave dispersion relation and neutron-scattering cross section for strongly anisotropic magnets is formulated in terms of effective renormalized exchange and anisotropy parameters. The spin-wave dispersion for the cone structure is considered in detail, including a diagonalization of off-diagonal wave-vector-dependent terms and renormalization effects caused by the crystal field. The derived expressions require no a priori knowledge about the crystal-field and magnetoelastic parameters. This is required for the application of the standard-basis-operator theory. A comprehensive analysis of the spin-wave data on Gd, Tb, Dy, and Er yields the interatomic exchange parameters and the effective anisotropy constants. The exchange parameters obey the de Gennes scaling and decrease as the cubed inverse distance, as expected for the isotropic Rudermann-Kittel interaction. Therefore, there is not much room for an unresolved two-ion anisotropy. The cone spin-wave data for Er can be accounted for on the basis of an isotropic exchange interaction and crystal-field parameters with magnitudes in quantitative agreement with those derived from static measurements on dilute ${\mathrm{Er}}_{c}\ensuremath{-}{\mathrm{Y}}_{1\ensuremath{-}c}$ alloys. No convincing evidence for a giant non-symmetry-breaking two-ion anisotropy has been found in Tb, Dy, and Er. A qualitative detection of a small symmetry-breaking two-ion anisotropy has been made in Tb and possibly also Dy and Er. The calculated and measured neutron-scattering intensities for Er are in good agreement, and the renormalization parameters calculated from known crystal-field parameters compare closely with those obtained from the fit to spin waves.

Magnetic excitations in HoFe2

Abstract: Spin wave and crystal field excitations in single crystal HoFe2 have been studied using inelastic neutron scattering. At 10 K [100] is the easy magnetic direction and at this temperature the acoustic spin wave mode exhibits a 0.60 meV gap due to anisotropy. The acoustic mode is degenerate at the zone boundary with a flat optic mode of energy 8.3 meV. The lack of dispersion in this mode is a consequence of the small (<.01 meV) Ho‐Ho exchange energy. A third mode is a highly dispersive optic mode which represents excitations of the iron sublattice spins and has a stiffness parameter almost identical to iron metal. A nearest neighbor linear spin wave model has been applied which represents the data of the three lowest modes well. This model predicts the remaining three allowed modes to be at energies above 200 meV. There is no measurable anisotropy in the spin wave modes with varying propagation directions. At room temperature, higher states of the Ho crystal field multiplet become populated and weaker dispersionless excitations between these levels are observed. The observed excitations are broadened beyond instrumental resolution because of contributions from several levels close together in energy. Crystal field calculations including exchange have been performed and are compared to the energies of the observed optic mode transitions.Spin wave and crystal field excitations in single crystal HoFe2 have been studied using inelastic neutron scattering. At 10 K [100] is the easy magnetic direction and at this temperature the acoustic spin wave mode exhibits a 0.60 meV gap due to anisotropy. The acoustic mode is degenerate at the zone boundary with a flat optic mode of energy 8.3 meV. The lack of dispersion in this mode is a consequence of the small (<.01 meV) Ho‐Ho exchange energy. A third mode is a highly dispersive optic mode which represents excitations of the iron sublattice spins and has a stiffness parameter almost identical to iron metal. A nearest neighbor linear spin wave model has been applied which represents the data of the three lowest modes well. This model predicts the remaining three allowed modes to be at energies above 200 meV. There is no measurable anisotropy in the spin wave modes with varying propagation directions. At room temperature, higher states of the Ho crystal field multiplet become populated and weaker dispe...

Spin Waves in Amorphous Ferromagnets

Abstract: The spin wave spectrum of dense random packing amorphous ferromagnets is discussed The genetal formula of spin wave stiffness parameter which appears in the long wavelength dispersion relation is given An explanation for the roton-like minimum observed in Mook's neutron diffraction measurement is also given within the quasicrystalline approximation

Spin waves in amorphous ferromagnets

Abstract: Spin waves in a model of an amorphous Heisenberg ferromagnet are studied by means of an effective medium approximation (EMA) for comparison with observations in amorphous transition metal–metalloid alloys. For long wave length and low energy the EMA agrees with a quasicrystalline approximation for the spin wave energy, but gives a larger density of states than an extended chain approximation with corresponds to conventional spin wave theory. The EMA also gives finite wave vector structure in the spectral weight function.

The transverse dynamical susceptibility of ferromagnets and antiferromagnets within the local exchange approximation

Abstract: Simple expressions for the transverse dynamical spin susceptibility are obtained within the local exchange approximation by neglecting local field effects. The nature and validity of this further approximation is discussed with particular reference to long-wavelength spin waves in a ferromagnet. This paper provides the first practical procedure for calculating the susceptibility solely from the results of a band calculation for the magnetically ordered groundstate.

Magnetoelastic and quadrupolar couplings in ErZn and HoZn

Abstract: The magnetisation curves of the cubic CsCl-type compounds ErZn and HoZn along the three principal symmetry directions are analysed taking into account magnetoelastic couplings and quadrupolar exchange interactions besides cubic crystal field and Heisenberg exchange. These additional second-order terms permit a good description of the anisotropy energy. The deduced coefficients are in agreement with the values necessary in the interpretation of the spin wave data in HoZn; they are consistent with other determinations such as magnetostriction and elastic constant measurements.

Spin wave dispersion of FeBO 3 at small wavevectors

Abstract: Brillouin scattering from thermally excited magnons and ferromagnetic resonance are used to determine the spin wave dispersion of the low-frequency spin wave branch in FeBO3, a transparent weak ferromagnet In addition to the dominant exchange and Zeeman contributions, the investigation takes into account magnetic dipole and magnetoelastic interactions Due to the antisymmetric exchange enhancement the material exhibits a broad spin wave band and a large gap energy at small magnetic fields Competing directional dependences of the dipole and the exchange energy produce a degeneracy of spin waves with a certain magnitude of the wavevector propagating in different directions The gap energy is shown to be due to magnetoelastic coupling, whereas the contribution of the anisotropy in the easy plane is negligible atT=300 K

Spin‐wave damping of domain walls in YFeO3

Abstract: The mobility of domain walls in YFeO3 is determined by calculating the damping of the uniform precession or k=0 spin‐wave mode. The presence of antisymmetric exchange is explicitly taken into account in obtaining the spin‐wave modes. The dominant spin‐wave damping mechanism is found to be a four‐magnon scattering process. This process leads to a calculated wall mobility that has the same order of magnitude and temperature dependence as that observed.

Spin wave resonance in single-crystal nickel films

Abstract: The room-temperature observation of extensive spin wave resonance spectra in (100) single-crystal nickel films is reported including the presence of surface spin wave modes. The variation of the spectrum with the angle between the applied magnetic field and the film normal is interpreted semiquantitatively in terms of Puszkarski's surface inhomogeneity models (1972). The value of the exchange constant D, is found to be 47+or-5*10-30 erg cm-2 for the applied field normal to the film surface.

Spin resonances in amorphous alloy films

Abstract: Spin resonance studies have been done on a series of amorphous thin films of Y‐Co, Zr‐Co, La‐Fe, Zr‐Fe and Lu‐Fe alloys prepared by co‐evaporation onto room temperature substrates. Y‐Co alloys behave in accord with static magnetic measurements. In Y29Co71 and Y20Co80 the exchange stiffness has been determined to be 0.6×10−6 and 0.4×10−6 erg/cm, respectively. Zr‐Co alloys, especially with high Co concentration show highly unexpected behavior by exhibiting several rather narrow resonances. The RE‐Fe alloys are also anomalous in that they give ferromagnetic resonances at 300 K while static measurements fail to show any evidence for long range order.

A Mossbauer investigation of Rb2FeF5: A one-dimensional antiferromagnetic system

Abstract: Mossbauer spectra of Rb2FeF5 show that it undergoes an ordering to a four sublattice antiferromagnetic state at 9.3+or-0.5K. The saturated value of the hyperfine field is 43.0+or-0.5 T, and is the same for both pairs of sublattices. This value is anomalously low for a high-spin ferric ion and corresponds to a zero-point spin reduction of about 28%. At finite temperatures the hyperfine fields at the iron nuclei are appreciably modified by the application of an external magnetic field. This behaviour is a characteristic of one-dimensional antiferromagnets. Relationships for the spin reduction as a function of the magnitude and direction of the external field are developed on the basis of spin wave theory. The measured values of the hyperfine fields are compared with those calculated from these relationships which leads to the ratio J'/J of the intrachain to interchain exchange constants being less than 10-3 and the ratio BA/BE of anisotropy to exchange fields being around 4*10-3.

Nuclear spin relaxation in normal liquid 3 He in contact with magnetic substrates

Abstract: We investigate the theory of longitudinal nuclear spin relaxation in the normal state of liquid 3He when the nuclear spins of the 3He are coupled to electronic moments in a substrate. We begin by deriving a general form for the relaxation rate in terms of spin correlation functions of the fluid and those of the spins in the substrate. The expression is applied to models which have formed the basis of recent theoretical discussions of the magnetic Kapitza conductance observed at very low temperature. We place considerable emphasis on the differences in the relaxation rate when the two spin systems are coupled by dipolar interactions and when they are coupled by isotropic interactions of exchange character. There are striking qualitative differences between these two cases in the model calculations. We also examine the general structure of the expressions for the nuclear relaxation rate and magnetic contribution to the Kapitza conductance to form model-insensitive conclusions about their temperature variation in special regimes of temperature. Finally, the results of our calculations are compared with the limited data available.

A study of spin fluctuations in antiferromagnetic metals described by a nesting-type model

Abstract: The effect of spin fluctuations in antiferromagnetic metals described by a nesting-type model is studied for paramagnetic states and for commensurate spin-density-wave states by the application of the renormalized spin fluctuation theory to the Rice model as well as to the Shibatani-Motizuki-Nagamiya model. Comparison is made between the spin fluctuation property in the nesting-type model and that in a band-type model; in the latter all the portions of the band are considered to be responsible for the antiferromagnetism. Although the effect of spin fluctuations in the nesting-type model is far less significant than that in the band-type model, this effect does become notable as the nesting between the two bands is made worse.

Spin density functional theory for the spin wave stiffness coefficient in ferromagnets

Abstract: The spin density functional theory is used to derive a variational principle (lower bound) for the wavevector dependent static transverse ferromagnetic spin susceptibility chi +-(q) for a general exchange-correlation energy functional. This variational principle is a direct consequence of the Hohenberg and Kohn minimum energy theorem for the ground state. The importance of spin rotational invariance is stressed in choosing the trial function so that the variational expression for chi +-(q) has the correct behaviour for small q. Noting the relationship between the spin wave stiffness coefficient D and chi +-(q), a rigorous upper bound for D is derived for general ferromagnetic systems. The relationships between the present general theory for D and recent theories based on the local exchange model are discussed.

Ground state configurations of a simple cubic array of pseudo-spins s = 1/2 with anisotropic exchange between nearest neighbours

Abstract: 2014The configurations of lowest energy of a system of pseudo-spins S = 1/2 forming a simple cubic lattice are analysed by considering the most general interaction, between nearest neighbours, allowed by a fourfold symmetry of the bond : Hij = J~ Siz Sjz + J (Six Sjx + Siy Sjy) for a pair (i, j) oriented along the z axis. In zero external field, the most stable configuration is either ferromagnetic when J~ and J are both negative, or antiferromagnetic in the other cases; in the latter situation various antiferromagnetic configurations are obtained depending on the signs of J~ and J. For all these configurations, derived in a classical way, the spin wave spectrum is calculated in order to check the magnetic stability of the system as well as to evaluate the quantum ground state energy and the mean spin deviation in this ground state. It is also shown that when J~ = 2014 J 0, the antiferromagnetic ground configuration is an eigenstate of the total Hamiltonian. Thus a new three dimensional magnetic system, whose ground state is known exactly, is obtained. LE JOURNAL DE PHYSIQUE TOME 39, JUILLET 1978, Classification Physics Abstracts 75.1OJ 75.30D .

Influence of the spin-wave linewidth on the spin-wave propagation direction for parallel pumping in single crystal YIG

Abstract: The peculiar secondary minimum in the parallel pump butterfly curve for [110] magnetized single crystal YIG, originally discovered by Sethares and coworkers, has been experimentally and theoretically investigated Data were obtained for an in-plane [110] magnetized

SPECIFIC HEAT OF THE QUASI 2D-XY HELIMAGNETS BaCo2(AsO4)2 AND BaCo2 (PO4)2

Abstract: We measured the magnetic specific heat of two quasi-two-dimensional (2-D), XY helimagnets, BaCo2 (AsO4)2 and BaCo2(PO4)2. At temperatures T < 2 K, C is proportional to T2 as expected from spin wave theory. At higher temperatures C has an exponential form characteristic of a potential barrier. The specific heat of BaCo2 (AsO4)2 exhibits a sharp anomaly at TN = 5.29 K whereas only a bump is observed around 5.5 K in BaCo2(PO4)2.