Showing papers on "Spin wave published in 1985"
TL;DR: Application of small static magnetic fields results in a Hanle effect which permits determination of the spin-relaxation time, and the unique features of the method should make it applicable to a wide range of studies.
Abstract: The strong inequivalence of spin-up and spin-down subbands in a ferromagnet causes a coupling between the charge and spin transport across the interface of a ferromagnetic and a contiguous paramagnetic metal. This allows the use of sensitive electronic measurements to probe spin transport. Application of small static magnetic fields results in a Hanle effect which permits determination of the spin-relaxation time ${\mathrm{T}}_{2}$. The unique features of the method should make it applicable to a wide range of studies.
1,151 citations
Book•
01 Jan 1985
TL;DR: In this article, Hartree-Fock-RPA theory was extended to the case of weakly and nearly Ferro-and Antiferromagnetic Metals and showed that it is possible to detect the presence of spin-fluctuations in these two types of materials.
Abstract: 1 Introduction- 11 Local Magnetic Moment and the Weiss Theory of Ferromagnetism- 12 Magnetic Moments of Atoms- 13 Heisenberg Localized Electron Model- 14 Itinerant Electron Model- 15 Localized vs Itinerant Electron Models- 16 Random-Phase Approximation Theory of Spin Fluctuations in Itinerant Electron Magnets- 17 Local Moments in Metals- 18 Self-Consistent Renormalization Theory of Spin Fluctuations and Weakly Ferro- and Antiferromagnetic Metals- 19 Unified Picture of Magnetism- 110 Organization of the Book- 2 Mean-Field Theory of Itinerant Electron Magnetism- 21 Model Hamiltonians- 22 Ferromagnetism- 23 Antiferromagnetism- 24 Spin-Density Waves- 25 Stability of Various Spin Orderings- 3 Dynamical Mean-Field Theory of Spin Fluctuations- 31 Stoner Excitations and Spin Waves in Ferromagnetic Metals- 32 General Spin Fluctuations and Dynamical Susceptibilities- 33 Critical Spin Fluctuations- 34 Antiferromagnets- 35 Limitations of the Hartree-Fock-RPA Theory- 4 Self-Consistent Renormalization (SCR) Theory of Spin Fluctuations- 41 Expressions for the Free Energy of an Interacting Electron System- 42 Paramagnon Theories- 43 SCR Theory of Ferromagnetic Metals- 431 Curie Temperature and Magnetic Susceptibility Above TC- 432 Analytical Explanation of the New CW Law- 433 Magnetization Below TC- 434 Rotationally Invariant Treatment- 44 Phenomenological Mode-Mode Coupling Theory- 45 SCR Theory of Antiferro- and Helimagnetic Metals- 46 Physical Origin of the New Curie-Weiss Susceptibility- 461 Temperature Variation of the Mean-Square Local Amplitude of Spin Fluctuation- 462 Spatial Spin Correlation- 47 Coexistence of and Phase Transitions Between Ferro- and Antiferromagnetism- 48 Quantitative Aspects of the SCR Theory for Weak Itinerant Ferromagnets- 5 Physical Properties of Weakly and Nearly Ferro- and Antiferromagnetic Metals- 51 Properties of Spin Fluctuations- 52 Thermal Expansion- 53 Specific Heat- 54 Nuclear Spin Relaxation- 541 Weakly and Nearly Ferromagnetic Metals- 542 Weakly and Nearly Antiferromagnetic Metals- 55 Electrical and Thermal Resistivities and Magnetoresistance- 551 Weakly and Nearly Ferromagnetic Metals- 552 Antiferromagnets- 56 Coupling Between Spin and Charge Density Fluctuations- 6 Local Magnetic Moments- 61 Local Moments in Insulator Magnets- 62 Metal-Insulator (Mott) Transition- 63 s-d or s-f Exchange Model- 64 Local Moment Formation in Metals- 641 Virtual Bound State- 642 The Anderson Model- 643 The Wolff-Clogston Tight-Binding Model- 65 Physical Properties of a Single Local Moment in Metals- 66 Interaction Between a Pair of Local Moments in Metals- 67 Local Moment Description of Magnetic Transition Metals- 7 A Unified Theory and Its General Consequences- 71 General Considerations Toward a Unified Theory- 72 A Phenomenological Description of the Unified Theory- 73 General Mechanism for the Curie-Weiss Susceptibility- 731 A Mean Mode-Mode Coupling Theory of Magnetic Susceptibility- 732 General Expressions for the Curie Temperature and Susceptibility- 733 Spin Correlations and Magnetic Susceptibility- 74 Possibility for Systematic Analyses of Experimental Results- 75 Temperature Variation of the Local Amplitude of Spin Fluctuation- 751 General Remarks- 752 Temperature-Induced Local Moments- 76 Limitations of the Adiabatic Approximation- 8 Functional Integral Theory- 81 Basic Formalism- 82 Local Moment in Metals- 83 Band Magnetism - A General Formalism- 84 Methods of Calculating the Free Energy Functional- 841 A Closed-Form Expression for ? [?, ?]- 842 Long-Wavelength Approximations- 85 A Unified Description of Magnetism in Narrow-Band Systems- 86 Approximation Methods of Evaluating the Functional Integrals- 861 Unified Theory- 862 Molecular Field (Single-Site) Approximation- 863 Choice of Forms for the Interaction Hamiltonian- 87 Results of Numerical Calculations- 871 Ferromagnetic Transition Metals ?-Fe, Co, Ni- 872 Antiferromagnetic Transition Metals- 873 FeSi, Nearly Ferromagnetic Semiconductor- 874 Temperature-Induced Local Moments in CoS2, CoSe2- 875 Magnetovolume Effects- 88 Supplementary Discussions on Various Approaches and Physical Pictures- 881 The Hartree-Fock Theory for Excited States with Spatially Varying Spin Density- 882 Local Band Theory- 883 Persistence of Exchange Splitting of the Band Above TC- 9 Spin Fluctuations in d-Electron Systems- 91 Spin Fluctuations and Neutron-Scattering Measurements- 92 Local Moment Systems- 921 Heusler Alloys- 922 EuO- 93 Substances Close to the Local Moment Limit- 931 MnPt3, FePd3- 932 FePt3- 94 Substances Close to the Weakly Ferro- and Antiferromagnetic Limits- 941 MnSi- 942 Cr- 95 Substances in the Intermediate Regime: q-Space Description- 951 Fe3Pt- 952 CeFe2- 953 ?-Mn, ?-(FeMn), ?-Fe- 954 ?-Mn- 96 Ferromagnetic Transition Metals Fe, Co, and Ni- 97 Some Systematic Trends in Paramagnetic Scattering- 10 Toward a Unified Theory of Dynamical Spin Fluctuations- 101 General Considerations- 102 Green's Function Theory of Dynamical Susceptibilities- 103 Effect of Electron Lifetime on RPA-SCR Spin Fluctuations- 11 Concluding Remarks- References
132 citations
123 citations
118 citations
TL;DR: In this article, a review of the results obtained on two ribbon-form metallic glass systems (Fe x Ni 1−x ) 75 P 16 B 5 Al 3 and Fe x B 1− x ) is presented.
Abstract: Neutron scattering has provided unique information about the nature of magnetism in amorphous alloys. This paper reviews some of the results obtained principally on two ribbon-form metallic glass systems - (Fe x Ni 1− x ) 75 P 16 B 5 Al 3 and Fe x B 1− x . The former exhibits three states depending on composition: pure ferromagnetism, re-entrant spin glass, and ordinary spin glass. The neutron results provide evidence for the coexistence of spin glass and ferromagnetic correlations in the intermediate regime. The alloys of Fe and B show Invar phenomena which result in anomalously small values of the effective spin-wave stiffness calculated from low-temperature magnetization and Mossbauer data. The long-wavelength spin waves as measured by the neutrons do not reflect the rapid demagnetization found in the bulk results, implying the presence of excitation processes other than long-wave-length spin waves.
112 citations
TL;DR: The one-dimensional quantum Heisenberg antiferromagnet with exchange alternation is related to the nonlinear 0(3) sigma model with a topological "θ term" in the Langrangian as discussed by the authors.
Abstract: The one‐dimensional quantum Heisenberg antiferromagnet with exchange alternation is related to the nonlinear 0(3) sigma model with a topological ‘‘θ term’’ in the Langrangian. The models with parity symmetry (θ=0 or π) are respectively related to the integer and half‐integer spin models without exchange alternation. The nonlinear quantum physics of Heisenberg antiferromagnets is placed in a wider context of topologically nontrivial field theories and the spin‐Peierls effect in half‐integer spin systems (and its absence in integer spin systems) explained.
88 citations
TL;DR: In this article, the spin-wave spectra for nickel over much of the zone for the [111] and [100] directions were measured and compared with recent theoretical calculations.
Abstract: Improvements in neutron spectroscopy have made possible measurements of the spin-wave spectra for nickel over much of the zone for the [111] and [100] directions. Broadening of the spin-wave excitations has been directly observed for the [111] direction and the nature of the optical spin wave has been further characterized for the [100] direction. Comparison of the measured results is made with recent theoretical calculations.
79 citations
TL;DR: The ferromagnetic resonance spectrum of a layered magnetic thin film is expected to show a number of standing spin-wave resonances with a wavelength that matches the thickness of the film as mentioned in this paper.
Abstract: The ferromagnetic resonance spectrum of a layered magnetic thin film is expected to show a number of standing spin‐wave resonances with a wavelength that matches the thickness of the film. For the case of perpendicular resonance such spectra were calculated for some typical films in which magnetic layers are alternated with weaker magnetic layers. Some useful approximations are discussed. The results of the calculations are compared with experimental perpendicular spectra measured on films in which fifty Permalloy layers alternate with Ni layers.
74 citations
TL;DR: In this article, the authors studied the spin-wave modes in magnetic multilayers and found that the amount of exchange can be tailored by choosing the proper materials or thickness for the nonmagnetic intermediate layers between the magnetic films.
Abstract: Spin‐wave modes in magnetic multilayers are of interest both for basic research and for application—for example, in microwave devices. Here I would like to discuss some ways to manipulate the mode spectra of such multilayers. One way, for example, would be to have reversed magnetization direction in adjacent layers which can be achieved by tailoring the coercive forces of the films in a proper way. The mode spectrum of such a system has been derived only recently and I would like to report a few important results. Also I would like to discuss the case where the films are coupled by exchange as well as by the dipolar interaction which is always there. Here the amount of exchange can be tailored by choosing the proper materials or thickness for the nonmagnetic intermediate layers between the magnetic films. We have studied these effects for a couple of Fe sandwiches with intermediate layers of various materials and find a short coupling length (<5 A) for V and Cr, and a long one (≲20 A) for Cu, Ag, Au, and ...
73 citations
TL;DR: The spin structures and magnetization curves of R 2 Fe 14 B (R: rare earth atom) are calculated on a basis of a simplified Hamiltonian as discussed by the authors, and favorable parameters are found that reproduce the observed spin structure, the magnetization curve and the spin reorientation temperature.
71 citations
TL;DR: In this article, the spin green functions in narrow band ferromagnets are calculated in linear approximation with respect to the current carrier concentration at zero temperature, and the generalisation of these expressions for the case of finite concentrations and temperatures is carried out by means of the 1/z expansion, z being the nearest-neighbour number.
Abstract: Spin Green functions in narrow band ferromagnets are calculated within the Hubbard model and s-d exchange model. The exact expressions are obtained in linear approximation with respect to the current carrier concentration at zero temperature. The generalisation of these expressions for the case of finite concentrations and temperatures is carried out by means of the 1/z expansion, z being the nearest-neighbour number. The spin wave damping, temperature dependence of the spin wave stiffness and the stability of the saturated ferromagnetic state in the Hubbard model are investigated. The rate of the longitudinal nuclear magnetic relaxation in the saturated conducting ferromagnet is calculated.
TL;DR: In this article, specific heat measurements have been done on the samples of Ce 1- x La x B 6 (x = 0, 0.03,0.10 and 0.25) under the magnetic field of 0, 6 and 36 kOe.
Abstract: Specific heat measurements have been done on the samples of Ce 1- x La x B 6 ( x =0, 0.03, 0.10 and 0.25) at low temperatures down to 0.1 K under the magnetic field of 0, 6 and 36 kOe. In the ordered state specific heat consists of a T 3 -term and a large γ T -term. The former originates from the excitation of antiferromagnetic spin wave and the latter is common in the dense Kondo systems. The γ-value is insensitive to the La-doping and the applied magnetic field as well as the type of magnetic ordering. The result is consistent with the \(\varGamma_{8}\) ground level model but with a substantial distortion. The present result is also consistent with the temperature dependence of resistivity in the same temperature range.
TL;DR: In this article, the spin dynamics of spin-polarized Fermi gases with arbitrary degrees of degeneracy are investigated and the spinwave spectrum, phenomenological diffusion coefficients and the macroscopic equation of motion for the magnetic moment are derived.
TL;DR: The spin-wave spectrum of a ferromagnetic multilayer with alternating directions of magnetization is derived in the dipolar magnetostatic limit and the solutions can be classified as bulklike or surfacelike with respect to the whole multilayers.
Abstract: The spin-wave spectrum of a ferromagnetic multilayer with alternating directions of magnetization is derived in the dipolar magnetostatic limit. The external magnetic field is set equal to zero and the magnetization is assumed to be in-plane but reversed in adjacent films. We find interesting qualitative differences for an even and an odd number N of single layers which constitute the multilayer. The solutions can be classified as bulklike or surfacelike with respect to the whole multilayer. As N\ensuremath{\rightarrow}\ensuremath{\infty} the bulklike solutions form bands. We also discuss some symmetry aspects of these solutions.
TL;DR: In this paper, high-resolution neutron scattering measurements, utilizing full polarization analysis techniques, have been carried out to explore the nature of the magnetic response above Tc in these itinerant ferromagnets.
Abstract: High‐resolution neutron scattering measurements, utilizing full polarization analysis techniques, have been carried out to explore the nature of the magnetic response above Tc in these itinerant ferromagnets. Large isotopically enriched single crystals were employed in order to obtain reliable determinations of the scattering function S(q,E). The scattering in Ni is found to evolve in a continuous fashion from the well‐known spin diffusion response at small wave vectors q to a response with peaks centered at ±E at larger q, in agreement with our original work. The ratio of the observed widths of these spin waves to the spin‐wave energies, as determined directly from measurements at constant q, is found to decrease with increasing ‖q‖ as expected. We also show that the recent measurements by Shirane and collaborators were taken with resolution which was too coarse to observe these spin‐wave excitations.
TL;DR: Ferromagnetic resonance of Permalloy in the bilayer system Ni 0.80Fe 0.20/Mn 0.50 has been used as a probe of the exchange anisotropy at the interface between the ferromagnetic Perm alloy layer and the antiferromagnetic manganese iron as mentioned in this paper.
Abstract: Ferromagnetic resonance of Permalloy in the bilayer system Ni0.80Fe0.20/Mn0.50Fe0.50 has been used as a probe of the exchange anisotropy at the interface between the ferromagnetic Permalloy layer and the antiferromagnetic manganese iron. For rotation of the applied magnetic field in the plane of the film, the resonance condition exhibits a unidirectional anisotropy which relates directly to the exchange bias field, as measured, for example, by the shift of the hysteresis loop. In the perpendicular orientation, and for Permalloy layer thicknesses greater than about 400 A, one or more standing spin wave modes are seen in addition to the uniform FMR. The indexing of these modes permit an evaluation of the boundary condition at the ferromagnet/antiferromagnet interface, in terms of partial spin pinning.
TL;DR: A spin-coherent representation is used to derive the spectrum of nonlinear excitations in a spin-S quantum ferromagnetic Heisenberg chain in the continuum limit and the stability of these excitations is discussed.
Abstract: We use a spin-coherent representation to derive the spectrum of nonlinear excitations in a spin-S quantum ferromagnetic Heisenberg chain in the continuum limit. Quantum effects split the semiclassical spectrum into two branches---a lower branch of spin-wave-like, large-width solitary waves with negligible quantum corrections for all S, and an upper branch of particlelike, small-width solitary waves subject to significant quantum corrections for low S. The stability of these excitations is briefly discussed.
TL;DR: The prediction of the dispersion curve and peak widths is in general agreement with data from subsequent neutron-scattering experiments, providing additional evidence that the ''average'' spin-splitting energy for nickel is in the 300- to 400-meV range.
Abstract: Results from recent calculations of the neutron-scattering cross section for energy transfer up to 1 eV have led to a new picture of spin waves in nickel, one in which spin waves exist out to the zone boundary. Our prediction of the dispersion curve and peak widths is in general agreement with data from subsequent neutron-scattering experiments. This provides additional evidence that the ''average'' spin-splitting energy for nickel is in the 300- to 400-meV range.
TL;DR: In this paper, the experiments of Gibson and Jeffries on ferromagnetic resonance at very high signal powers are simulated with a model involving coupling of only one spin wave to the uniform mode.
Abstract: The experiments of Gibson and Jeffries on ferromagnetic resonance at very high signal powers are simulated with a model involving coupling of only one spin wave to the uniform mode. Bifurcation sequences and chaos similar to the ones observed are found in the computation.
TL;DR: Iron is an ideal candidate for a novel high- energy-transfer experiment on recently developed high-energy neutron sources and spin-wave modes with energies up to 750 meV are predicted.
Abstract: Calculations have been made of inelastic neutron-scattering cross sections for ferromagnetic iron. Quite unexpectedly, a rich picture of high-energy collective excitations has emerged. In particular, ''optic'' spin-wave modes with energies ranging to about 750 meV are predicted. Thus, iron is an ideal candidate for a novel high-energy-transfer experiment on recently developed high-energy neutron sources.
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.
TL;DR: In this article, the authors obtained the leading quantum corrections in S-1 to the ground-state energy and to the spin wave spectrum of a Heisenberg helimagnet, and they found that the helix wavevector Q is not modified and the spin-wave spectrum has the correct soft-mode behavior (the Goldstone mode) at k=0 and k=+orQ as they have explicitly verified for the anisotropic next-nearest-neighbour heisenberg mode.
Abstract: The authors obtain the leading quantum corrections in S-1 to the ground-state energy and to the spin wave spectrum of a Heisenberg helimagnet. Both single and double scattering processes contribute. They find that the helix wavevector Q is not modified and the spin wave spectrum has the correct soft-mode behavior (the Goldstone mode) at k=0 and k=+or-Q as they have explicitly verified for the anisotropic next-nearest-neighbour Heisenberg mode. The Goldstone theorem for helimagnets is also briefly considered.
TL;DR: In this paper, a new formula for the spin-wave stiffness constant D was derived and compared with previous work, and it was shown that in NiD is very sensitive to the 'ground-state' exchange splitting Delta in the d band and that hybridisation with the sp band has little effect on D.
Abstract: A new formula is derived for the spin-wave stiffness constant D and is compared with previous work. It is shown that in NiD is very sensitive to the 'ground-state' exchange splitting Delta in the d band and that hybridisation with the sp band has little effect on D. The observed value of D yields a value of 0.40 eV for Delta , which is larger than the observed quasiparticle exchange splitting of 0.33 eV, as expected theoretically. Calculations on D in Ni alloys, within the virtual crystal approximation, are compared with experimental results on NiCo and NiFe.
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.
TL;DR: In this paper, the spin wave theory was used to determine the ground state of a face centered cubic lattice with nearest neighbor antiferromagnetic Heisenberg interactions, in which the energy E g and spin reduction were calculated.
Abstract: The classical ground states of face centered cubic lattice with nearest neighbor antiferromagnetic Heisenberg interactions are shown to have continuous degeneracy. The spin wave theory removes the degeneracy and determines the ground state, in which the energy E g and spin reduction are calculated. E g is also obtained by calculating the lowest energy of finite size systems and extrapolating to infinite lattice. Both results are in fairly good agreement with each other. Finally it is concluded that the sublattice long range order exists.
TL;DR: In this paper, the spin correlations in a cluster type spin glass of 90FeTiO 3 −10Fe 2 O 3 have been studied by neutron small and high angle scattering from a single crystal.
Abstract: The spin correlations in a cluster type spin glass of 90FeTiO 3 –10Fe 2 O 3 have been studied by neutron small and high angle scattering from a single crystal. The magnetic correlations of the moments parallel and perpendicular to the c axis, and have been separately determined and the spin configuration inside the cluster as well as the cluster configuration have been determined. The spin glass transition temperature has been found to correspond to the temperature where the spin axis inside the cluster aligns in the c axis and the antiferromagnetic modulation starts to occur inside the cluster.
TL;DR: In this article, the problem of describing electron states in the s-f model of a ferromagnetic semiconductor at low temperatures is considered in the case of finite conduction band filling.
Abstract: For pt.I see ibid., vol.17, p.669 (1984). The problem of the description of electron states in the s-f model of a ferromagnetic semiconductor at low temperatures is considered in the case of finite conduction band filling. The spectrum, damping, density of states and spin polarisation of conduction electrons are investigated. It is demonstrated that the leading temperature-dependent corrections to the spectrum and the total density of states are proportional to T52/.
TL;DR: In this paper, two different static in-plane kink structures, which are symmetric with respect to a given spin or a given bond of the chain, respectively, were found.
Abstract: Discrete ferromagnetic spin chains with planar single-ion and exchange anisotropy and with an externaldc fieldB applied in the easy plane are considered in the classical limit. We find two different static in-plane kink structures, which are symmetric with respect to a given spin or to a given bond of the chain, respectively. The first structure is unstable against in-plane fluctuations for all applied fields. The second one, on the other hand, exists (independent of the anisotropy parameters) only up to a critical fieldB
e
and is stable against in-plane fluctuations in its whole domain of existence. Depending on the anisotropy parameters, this latter configuration may, however, become unstable against out-of-plane fluctuations at a critical valueB
c
TL;DR: In this article, an NMR technique where these oscillatory modes are directly excited and detected, with the use of two sets of radiofrequency coils (for induction and detection), each connected in opposition in order to create or detect pure magnetization gradients over the sample.
Abstract: In gaseous spin-polarized 3He at low temperature, spin-diffusion becomes oscillatory and gives rise to spin waves; these waves have a quality factor μM, where M is the (relative) nuclear magnetization and μ a dimensionless coefficient characteristic of the importance of exchange effects in binary collisions. We describe here an NMR technique where these oscillatory modes are directly excited and detected, with the use of two sets of radiofrequency coils (for induction and detection), each connected in opposition in order to create or detect pure magnetization gradients over the sample. The measurements of μ are in good agreement with theory as well as with previous experiments, but only at temperatures above 2 K; below, the measurements are affected by processes which are not fully understood, probably related to the formation of a 3He monolayer on the surface of the coating of solid hydrogen which covers the inner surface of the cell.