Showing papers on "Spin wave published in 1979"
01 Jan 1979
TL;DR: In this article, the authors present an approach to perturbation approach to Lattice Instabilities in Quasi-One-Dimensional Conductors (QODC) in the context of TTF-TCNQ.
Abstract: 1 Introduction to Highly Conducting One-Dimensional Solids.- 1. Introduction.- 2. Some Preliminary Thoughts.- 3. Excitonic Superconductivity.- 4. TCNQ Salts and KCP.- 4.1. NMP-TCNQ.- 4.2. TTF-TCNQ.- 4.3. KCP.- 5. TTF-TCNQ and TSeF-TCNQ.- 5.1. Structural Transitions in TTF-TCNQ.- 5.2. Electromagnetic Properties of TTF-TCNQ.- 5.3. ESR and Alloys of TTF-TCNQ and TSeF-TCNQ.- 6. Theory.- 7. Some Concluding Thoughts.- References.- 2 X-Ray and Neutron Scattering from One-Dimensional Conductors.- 1. Introduction.- 1.1. Lattice Instabilities and Phonon Anomalies.- 1.2. X-Ray Diffuse Scattering.- 1.3. Neutron Scattering.- 2. Structural Studies of KCP and Related Platinum Chain Complexes.- 2.1. Structure and One-Dimensional Electrical Properties of KCP.- 2.2. X-Ray Diffuse Scattering from KCP.- 2.3. Neutron Scattering Studies of KCP.- 2.4. Study of Other Platinum Complexes.- 3. Structural Studies of Organic One-Dimensional Conductors.- 3.1. Structure and TTF-TCNQ Crystals.- 3.2. High-Temperature Precursor Scattering in TTF-TCNQ.- 3.3. The Modulated Phases of TTF-TCNQ.- 3.4. Spin Waves in TTF-TCNQ?.- 3.5. The Interpretation of the Sequence of Modulated Phases in TTF-TCNQ.- 3.6. Study of Other Organic One-Dimensional Conductors.- 4. Concluding Remarks.- References and Notes.- 3 Charge-Density Wave Phenomena in One-Dimensional Metals: TTF-TCNQ and Related Organic Conductors.- 1. Introduction.- 2. Strength of Interactions Bandwidth, Electron-Electron and Electron-Phonon Interactions.- 2.1. One-Electron Energies Band Structure.- 2.2. Electron-Electron Interactions: Nuclear Magnetic Resonance and Magnetic Susceptibility.- 2.3. Electron-Phonon Interaction.- 3. The Peierls Instability in TTF-TCNQ: Structural Aspects and Phonon Softening.- 4. The Pseudogap: Optical Properties.- 5. Electrical Conductivity.- 5.1. DC Measurements.- 5.2. Microwave Measurements.- 6. The Transition Region 38 K
745 citations
TL;DR: In this paper, a discussion of surface state theory and experimentally observed effects of spin wave resonance on thin magnetic films is given, starting from the general model assumptions made when dealing with thin magnetic film, concentrates specifically on the Surface Inhomogeneity Model, for which a Hamiltonian is established and diagonalized, leading to the elementary magnetic excitation of the system.
195 citations
TL;DR: In this article, the spin wave spectrum of the helical phases has a large density of states at low frequency due to the presence of saddle points in the spectrum or of a soft branch.
Abstract: The phase diagram at T = 0 K and the spin wave spectrum is studied for magnetic models appropriate for certain layer compounds of transition metals. Heisenberg and XY exchange is considered with interaction up to third neighbours in the basal plane. We consider only the case of nearest neighbour (n.n.) ferromagnetic interaction. Noncollinear order (helical phases) can easily occur when the interaction between more distant neighbours is antiferromagnetic. The following lattices are considered: square, triangular, honeycomb, tetragonal, exagonal and rhombohedral. Under certain conditions the spin wave spectrum of the helical phases has a large density of states at low frequency due to the presence of saddle points in the spectrum or of a “soft branch”. Models for NiBr2 and BaCo2(AsO4)2 are considered.
140 citations
TL;DR: In this paper, the authors reported direct measurements of the time-dependent spin correlation function S(k, t) for a Cu-Mn spin glass alloy over nearly 3 decades of time in a single scan in the range 10-12 < t < 10-9s.
114 citations
TL;DR: In this article, light scattering measurements on thin polycrystalline samples of iron and nickel were performed and both the surface and bulk magnons were observed, and the measured magnon energies as a function of magnetic field, and of wavevector magnitude and direction, were in good agreement with the calculated values.
Abstract: We report on light scattering measurements on thin polycrystalline samples of iron and nickel. Both the surface and bulk magnons are observed. The measured magnon energies as a function of magnetic field, and of wavevector magnitude and direction, are in good agreement with the calculated values. The predicted exchange induced decay of the surface magnon is observed. In nickel the observed frequencies and linewidths are strongly strain dependent. Oxide layers have an almost negligible effect on the spin wave frequencies in both iron and nickel.
73 citations
TL;DR: In this paper, the authors analyzed the temperature-dependent part of the relaxation rate of conduction-electron spin in simple metals and compared the experimentally measured ESR linewidth of Na, K, Rb, Cs, Cu, Ag, Au, Al, Be, and Mg by scaling it with the inverse of the square of the spin-orbit perturbation.
Abstract: We analyze the temperature-dependent part of the relaxation rate of conduction-electron spin in simple metals. According to the model of Elliott and Yafet the electron-spin-resonance (ESR) linewidth has the same temperature dependence as the resistivity. We have compared the experimentally measured ESR linewidth of Na, K, Rb, Cs, Cu, Ag, Au, Al, Be, and Mg by scaling it with the inverse of the square of the spin-orbit perturbation and plotting it versus reduced temperature, that is, $\frac{T}{{T}_{\mathrm{Debye}}}$. A universal, Gr\"uneisen-like curve is indeed followed by the monovalent metals, but large deviations appear in the cases of Al, Mg, and Be. The implications of these behaviors are discussed.
67 citations
TL;DR: In this article, the authors measured the temperature dependence of the Landau-Lifshitz damping parameter λ in nickel and found that the magnitude of λ increased by a factor 4 over the temperature range 300 K −77 K.
Abstract: Using the technique of microwave transmission at FMAR, we have measured the temperature dependence of the Landau‐Lifshitz damping parameter λ in nickel. It was found that the magnitude of λ increased by a factor 4 over the temperature range 300 K–77 K. The microscopic theory of spin wave damping indicates that there are two contributions to the damping parameter; the one proportional to the resistivity and the other to the wave number dependent conductivity. We compare our experimental results with this theory and with the previous work of Bhagat using FMR.
66 citations
TL;DR: In this article, the second sound in the $A$1$ phase of superfluid He$ has a velocity three orders of magnitude larger than in the$A$ phase and is at the same time a spin wave.
Abstract: Second sound in the ${A}_{1}$ phase of superfluid $^{3}\mathrm{He}$ has a velocity three orders of magnitude larger than in the $A$ phase and is at the same time a spin wave. A magnetic field inhomogeneity leads, depending on the geometry, either to a pressure or temperature difference. These results, among others, contradict predictions by previous authors and are obtained from the hydrodynamic theory derived in this Letter by employing the concept of broken relative symmetry.
52 citations
TL;DR: In this article, the authors show that coupling of propagating magnetostatic waves with resonant exchange dominated spin wave modes produces attenuation notches in the magnetic wave transmission response, where the exchange resonances occur when kex = nπ/d, where kex is the exchange wave number normal to the film plane, n is the mode number and d is the thickness of epitaxial YIG film.
Abstract: Coupling of propagating magnetostatic waves with resonant exchange dominated spin wave modes produces attenuation notches in the magnetostatic wave transmission response. The exchange resonances occur when kex=nπ/d, where kex is the exchange wave number normal to the film plane, n is the mode number and d is the thickness of the epitaxial YIG film. Measurements of attenuation notch depth and position have been performed on as grown LPE‐YIG films and on films whose surface spins were pinned by ion milling, SiO2 deposition or annealing. Coupling was strongest for magnetostatic volume waves with the magnetic bias field normal to the film. Coupling to magnetostatic surface waves was less strong and in accordance with theory magnetostatic volume waves propagating parallel to the magnetic bias field showed zero coupling. The various treatments increased the depth of the attenuation notches and produced a mode pattern consistent with spin pinning asymmetric between the two film surfaces. The probable source of c...
43 citations
TL;DR: In this article, the sine-Gordon equation is applied to the dynamics of a 1D-ferromagnetic chain with planar anisotropy in a symmetry-breaking field (magnetic field perpendicular to the chain direction).
Abstract: It has been suggested that in systems with strong fluctuations as around a critical point strongly nonlinear effects should occur. The simplest possible equation for nonlinear dynamics is the sine‐Gordon equation. This equation can be applied to the dynamics of a 1‐D‐ferromagnetic chain with planar anisotropy in a symmetry‐breaking field (magnetic field perpendicular to the chain direction). The dynamics of such a system consist of two types of elementary excitations: nonlinear modes (solitons and breathers) and linear modes (spin waves). The thermodynamics for the nonlinear modes are the same as for a gas of noninteracting relativistic quasi‐particles. In the frame of that picture the dynamic structure factor for an inelastic neutron scattering experiment can be calculated for the relativistic case, and it appears that inelastic n‐scattering is the most direct way for the observation of solitons. Experimental results, obtained for CsNiF3 are discussed and compared with the theoretical results. These experimental results show that nonlinear modes are indeed an essential part of the dynamics of that system.
42 citations
TL;DR: In this article, the connection between the phenomenological hydrodynamics and microscopic theories of superfluid 3He was investigated. But the only approximation made is the perturbative treatment of the very small magnetic dipole energy.
TL;DR: In this article, the spin wave spectrum is observed to be Ising-like with J / k =75 K, but the temperature dependence is unusual and the peak becomes broad and the intensity falls off with increasing temperature from the high q side.
Abstract: Following the previous study on the 1D Ising antiferrormagnet CsCoCl 3 , the dynamical spin correlation has been studied in a wide range of temperature. The observed spin wave spectrum is Ising-like with J / k =75 K but the temperature dependence is unusual. No softening of the spin wave frequencies occurs, but the peak becomes broad and the intensity falls off with increasing temperature from the high q side. Well behaved spin wave peaks whose wave lengths are much longer than the correlation length κ -1 can be observed. Discussions are given of the criteria for the existing of spin waves. The longitudinal correlation cannot be described by the simple rigorous solution of diffusive type with reasonable parameters especially at T <| J |/ k . Villain's theory of propagative relaxation is promising indicating importance of off-diagonal terms contained in the Hamiltonian.
TL;DR: In this article, the subsidiary absorption spinwave instability threshold hcrit in high-quality single crystals of yttrium iron garnet reveal anomalous structure over a field interval extending several hundred Oe below the butterfly curve minimum at Hc.
Abstract: Measurements of the subsidiary absorption spin‐wave instability threshold hcrit in high‐quality single crystals of yttrium iron garnet reveal anomalous structure over a field interval extending several hundred Oe below the butterfly curve minimum at Hc. Such measurements have now been extended to cover the entire butterfly curve for sphere and plate samples. At the low‐field end of the structure region, hcrit increases rapidly as the static field H is decreased to a ’’kink’’ field H′c. As H is reduced further, the increase in hcrit is much more gradual. The nature of the onset changes drastically at H′c, from a gradual increase to an abrupt jump in reflected power at threshold. Theoretical analysis of the data shows: (1) The instability at Hc is for spin waves with a polar angle ϑk of 22° rather than the 35° value often cited. (2) The field interval for the instability of zero wave number (k=0) modes is not confined to H≳Hc, but extends over a wide range down to H′c. (3) The kink at H′c corresponds to an ...
TL;DR: In this article, a theoretical study of the propagation of magnetoelastic waves in a ferromagnetic film bonded to a nonmagnetic substrate is presented, which correspond to both Rayleigh waves and Love waves modified by the magneto-elastic interaction.
Abstract: We present a theoretical study of the propagation of magnetoelastic waves in a ferromagnetic film bonded to a nonmagnetic substrate. We find magnetoelastic waves which correspond to both Rayleigh waves and Love waves modified by the magnetoelastic interaction. Deviations from the elastic‐wave characteristics are found in the frequency region where bulk and surface spin waves propagate. Most particularly, a rich, strongly frequency dependent, and highly nonreciprocal attenuation rate is found for these modes. The anomalies associated with the surface spin waves are very sensitive to spin pinning conditions.
Journal Article•
TL;DR: In this paper, Brillouin-scattering measurements of thermally excited acoustic-surface phonons, and bulk and surface magnons, in sputtered films of Fe1−x B x and Co1−X B x.
Abstract: We report on Brillouin‐scattering measurements of thermally excited acoustic‐surface phonons, and bulk and surface magnons, in sputtered films of Fe1−x B x and Co1−x B x . From the slope of the surface‐magnon frequency shift with field we determine g factors of 2.09±0.03 for Fe1−x B x and 2.16±0.03 for Co1−x B x , with no significant trend as a function of composition and no difference between amorphous and polycrystallinematerials. The magnetization for pure Fe and Co agree with literature values. The magnetization of sputtered and quenched materials of the same composition are in agreement provided both samples are amorphous. Effective exchange corrections of order D k 2=0.1–0.5 kOe (where D is the spin‐wave stiffness and k is a magnon‐wave vector) are needed to properly fit the dependence of bulk‐magnon frequency shift on field. The magnetization values determined with such fits agree within experimental error with magnetizations obtained from the surface magnons. Possible origins of the D k 2 correction are discussed. In films below about 200 nm in thickness, structure is observed in the bulk‐magnon peaks which may be due to standing spin waves. The potential of Brillouin scattering as a tool for thin‐film characterization is discussed.
TL;DR: In this paper, the functional integral method of the previous paper is generalized to allow a discussion of the dynamical spin fluctuations in itinerant-electron magnets, and the magnitude fluctuations and nonstatic spin fluctuations are treated as a perturbation on the nonlinearly interacting static spin fluctuations.
Abstract: The functional-integral method of the previous paper is generalized to allow a discussion of the dynamical spin fluctuations in itinerant-electron magnets. The magnitude fluctuations and nonstatic spin fluctuations are treated as a perturbation on the nonlinearly interacting static spin fluctuations. The result is a free energy which is a sum of a Stoner contribution together with correlation corrections, a classical Heisenberg free energy as found in the previous paper, and a quantum spin-wave free energy minus its zero-frequency part.
TL;DR: In this article, a spin density wave host, Cr and Cr-Mo 2, each containing 14% Fe, was used for neutron scattering, transport and magnetic measurements on two spin-density wave hosts, and the results showed that antiferromagnetism and spin glass ordering coexist at low temperatures.
Abstract: Neutron scattering, transport and magnetic measurements are presented on two spin density wave hosts, Cr and Cr-Mo 2%, each containing 14% Fe. The results show that in both systems antiferromagnetism and spin glass ordering coexist at low temperatures.
TL;DR: In this paper, the effect of replacing boron by carbon in Fe86B14 alloy was found to change significantly the temperature dependence of magnetization in the direction of increasing spin wave stiffness, and to reduce the saturation susceptibility.
Abstract: Temperature and magnetic field dependence of amorphous Fe‐B‐C alloys obtained by splat cooling were measured and compared with those of Fe‐B alloys. It was found that the effect of replacing boron by carbon in Fe86B14 alloy was to change significantly the temperature dependence of magnetization in the direction of increasing spin‐wave stiffness, and to reduce the saturation susceptibility. The high value of room temperature saturation induction found in Fe‐B‐C alloy is therefore attributed to a change in the temperature dependence of magnetization, rather than to change in the magnetic moment at 0 K.
TL;DR: The temperature dependence of easy axis magnetization in the ferromagnetic phase of MnP was measured to an accuracy of Δ M /M <±5 ×10 -4 over a range from 4.2 K to 280 K.
Abstract: The temperature dependence of the easy axis magnetization in the ferromagnetic phase of MnP is measured to an accuracy of Δ M / M <±5 ×10 -4 over a range from 4.2 K to 280 K. Instead of the usual T 3/2 law, T ln T dependence holds up to about T c /2. The following spin wave dispersion is expected to exsist at 0 K; along the a axis it is nearly constant up to q a = Q and increases very rapidly beyond Q , where Q is the screw propagation vector, while for perpendicular to the a axis it is quadratic in q ⊥ . At a finite temperature, the calculated two-magnon renormalization causes increase of the magnon energy near q a ∼ Q which induces an anomalous suppression for decrease of magnetization in MnP. The ferro-screw phase transition seems also to be due to this effect.
TL;DR: In this article, the authors measured magnetic excitations in the linear-chain antiferromagnet TMMC at T = 1.8 K and observed an energy gap at q = 0 associated with zz-spin correlations, thus giving direct evidence for the importance of the dipolar xy anisotropy for spin dynamics at low temperatures.
TL;DR: In this article, the temperature dependence of saturation magnetization in three glassy alloys was measured using ferromagnetic resonance and it was shown that the magnetization follows the relaxation M(T) =M0(1−BT3/2 −CT5/2) with B and C values fairly close to those obtained using Mossbauer and vibrating sample magnetometer techniques.
Abstract: We have used ferromagnetic resonance to measure the temperature dependence of the saturation magnetization in three glassy alloys: I: Fe29Ni49P14B6Si2 (Metglas 2826B), II: (Fe0.4Ni0,6)75P16B6Al3, and III: (Fe0.5Ni0.5)75P16B6Al3. In I we find that, for 4 ?T?300 K, the magnetization follows the relaxation M(T) =M0(1–BT3/2 −CT5/2) with B and C values fairly close to those obtained using Mossbauer and vibrating sample magnetometer techniques. For II and III it is necessary to include the effects of spin wave energy renormalization, with temperature, to account for the variation of M over a comparable temperature regime. That is, the parameter B obeys the relation: B(T) =B0[1/(1−αT5/2)]3/2. In terms of the spin wave stiffness this implies D=D0[1−β (T/Tc)5/2] meV‐A2 where, again, the parameter values are in the range found for similar systems by neutron scattering.
TL;DR: In this article, the equivalence of the Dyson-Maleev (DM), Holstein-Primakoff (HP) and matching-of-matrix-element (MME) transformations is proven.
Abstract: An exact perturbation expansion, to the order 1/S2, is derived for the Heisenberg ferromagnet. The equivalence of the Dyson-Maleev (DM), Holstein-Primakoff (HP) and matching-of-matrix-element (MME) transformations is proven. They give identical T5/2 and T4 coefficients. For the planar ferromagnet, an exact expansion in anisotropy against exchange field proves the equivalence of the HP and MME transformations. Several explicit results and numerical estimates are given.
TL;DR: In this paper, the spin-wave analysis is used to interpret the effects of magnetic anisotropy on the lineshapes of metallic glasses before and after annealing, and it is concluded that a model of dipolar-coupled regions which assume a common resonance frequency band is appropriate in ferromagnetic metallic glasses.
TL;DR: In this article, the spin wave energy dispersion in the (010) plane of the distorted perovskite KCuF3, which exhibits many magnetic properties of the spin-1/2 one-dimensional antiferromagnet, has been investigated at 4.7K (TN=39K).
Abstract: Using inelastic neutron scattering techniques, the spin wave energy dispersion in the (010) plane of the distorted perovskite KCuF3, which exhibits many magnetic properties of the spin-1/2 one-dimensional antiferromagnet, has been investigated at 4.7K (TN=39K). The measurements confirm the very strong exchange interaction between the spins in the (001) direction, and show that in this direction the expression for the excitation energies of the spin-1/2 antiferromagnetic chain given by des Cloizeaux and Pearson (1962) is obeyed. The exchange interaction between these chains is found to be only 1.6% of that within the chains.
TL;DR: In this paper, a new theoretical model is presented, in which the EuS conduction band consists of pure spin states and mixed spin states, each weighted with a temperature dependent spectral weight (reduced density of states).
TL;DR: In this article, the authors investigated two c-number initial value problems for the creation of spin waves in 3He A and 3He B and showed that both of them can be quantized and that the actual boundary conditions could prove important to the associated physics.
Abstract: Spin waves in 3He A are governed by the sine-Gordon equation. Its kink and breather solutions are elementary nonlinear excitations which generalize the usual concept of spin waves in a linearised theory.2 Spin waves in 3He B are governed by a non-integrable double sine-Gordon equation. This has two kink solutions with jumps 2? ? 4 cos-1 (-?) and 4? - 2?. As noted previously kinks always bump in collision; but 2? kink-antikink pairs convert to - (4? - 2?) antikink-kink pairs; 4? - 2? kink-antikink pairs bump below a velocity threshold V 0.92 in dimensionless units and convert to - 2? antikink-kink pairs above this threshold. A new result is that below V = 0.36 4? - 2? kink-antikink pairs bind into long lived breather-like states. If c-number theory is applicable in the form derived we expect the breathers in both 3He A and 3He B to play some role in the NMR response. But if the systems are quantised no breathers can be excited in 3He A and no breather-like states in 3He B. We investigate two c-number initial value problems for the creation of spin waves, one in 3He A, one in 3He B. The critical fields for homogeneous NMR in both systems are shown to remain critical fields for spatially inhomogeneous systems. For the chosen boundary and initial conditions only breathers are created below first threshold: these are standing waves in 3He A but move outwards in 3He B. For the chosen boundary conditions the ringing observed by Wheatley would have to be attributed to these breathers. We conclude from this on the one hand that the systems scarcely can be quantised and on the other that the actual boundary conditions could prove important to the associated physics. At first threshold ut = 3/2 3He B spin waves move outwards as single 4? - 2? kinks, as 4? - 2? kink-antikink pairs, or as combinations of these with outgoing breathers. In contrast it is above the single threshold at ut = 2 in 3He A that single 2? kinks first move out and any remaining breathers stand; more 2? kinks move out further above threshold. 3He B has a second threshold above which combinations of 4? - 2? kinks and antikinks and 2? kinks move outwards. The different behaviors of spin waves in the two systems 3He A and 3He B may permit a magnetic experiment which could help to confirm the different symmetries of the order parameters assigned to these different phases.
TL;DR: In this article, the magnetic excitations of the incommensurate spin-density wave in pure chromium have been investigated with use of inelastic neutron scattering, and the polarizations of these modes are found to be highly anisotropic.
Abstract: The magnetic excitations of the incommensurate spin-density wave in pure chromium have been ivestigated with use of inelastic neutron scattering. We have observed the spin wave modes originating from the incommensurate magnetic Bragg reflections. The polarizations of these modes are found to be highly anisotropic. We have also observed a new magnetic excitation centered at a commensurate wave vector. This new excitation is interpreted as a feature specific to a transverse incommensurate spin-density wave.
TL;DR: In this article, the first observation by neutron inelastic scattering of a collective elementary excitation in a metallic actinide compound was made, and the excitation is longitudinally polarized with respect to the direction of the magnetic moment, has a dispersion of 6.7 THzA, and has a most unusual temperature dependence.
Abstract: We report the first observation by neutron inelastic scattering of a collective elementary excitation in a metallic actinide compound. The excitation is longitudinally polarized with respect to the direction of the magnetic moment, has a dispersion of 6.7 THzA, and has a most unusual temperature dependence. Present models for the electronic structure of this and similar materials are inadequate to account for the dynamical behavior we have observed.
TL;DR: In this article, a method for determining the magnetic anisotropy profile of an ion-implanted garnet layer is presented, where the eigenvalue equation for spin waves is solved numerically for a system consisting of a very thick film with uniform perpendicular anisotropic and a surface layer in which the anishotropy varies through the surface.
Abstract: A method for determining the magnetic anisotropy profile of an ion‐implanted garnet layer is presented. To do this the eigenvalue equation for spin waves is solved numerically for a system consisting of a very thick film with uniform perpendicular anisotropy and a surface layer in which the anisotropy varies through the surface. Results of this calculation are matched to experimental FMR data from samples cut from the same wafer but etched by different amounts. A measurement of the exchange constant in the implanted layer may be possible if two or more surface modes are visible. The anisotropy profiles of samples implanted with 2×1014 Ne+/cm2 at 50, 100, and 150 keV were reconstructed in this manner. The profile was found to show a broad peak centered at a depth somewhat shallower than the projection range for Ne+ at the appropriate energy. The value of the change in anisotropy was shown to match that predicted from a magnetostrictive origin and the measured change in lattice constant in the surface layer...