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Showing papers on "Spin wave published in 1995"



Journal ArticleDOI
TL;DR: In this paper, the spin susceptibility and spin-lattice relaxation rate of 51 V nuclear moments of CaV 4 O 9 with tetragonal structure have been measured and the first example of quasi-two-dimensional spin systems with spin gap was provided.
Abstract: Spin susceptibility and spin-lattice relaxation rate of 51 V nuclear moments of CaV 4 O 9 with tetragonal structure have been measured. They exhibit characteristics of spin gap systems. This provides the first example of quasi-two-dimensional spin systems with spin gap.

174 citations


Journal ArticleDOI
TL;DR: In this paper, it was shown that the magnetoresistance ratio is roughly proportional to the product of spin polarizations of both ferromagnets and that the dependence of MR ratio, saturation resistance and conductance on temperature are also discussed.

136 citations


Journal ArticleDOI
TL;DR: In this paper and the following paper, results of inelastic neutron-scattering measurements made using the MARI time-of-flight spectrometer at the Rutherford Appleton Laboratory are reported.
Abstract: In this, and the following paper, we present the results of a detailed experimental investigation into the spin dynamics of the quasi-one-dimensional S=1/2 Heisenberg antiferromagnet ${\mathrm{KCuF}}_{3}$. In this paper we report results of inelastic neutron-scattering measurements made using the MARI time-of-flight spectrometer at the Rutherford Appleton Laboratory. Measurement of the magnetic excitation spectrum was made in both the low-temperature phase, where the chains are ordered together, and in the high-temperature phase, where the correlations between chains become unimportant. We compare our measurements with the M\"uller ansatz, which is identified with a two-spinon cross section, and find excellent agreement with this. The effect of temperature on the excitation continuum was also investigated. A series of measurements were made at temperatures ranging from 20 to 200 K. These results are compared to the predictions of field theory for the one-dimensional Heisenberg chain. Again good agreement is found with the theoretical predictions. In the following paper measurements of the low-energy scattering in the ordered phase, made on a triple-axis spectrometer, are presented.

129 citations


Journal ArticleDOI
TL;DR: I present the exact dispersion relations for certain low-lying states of the one-dimensional Heisenberg ferromagnet, which are the states with the lowest energy for given values of the total spin, component of spin and momentum.
Abstract: I present the exact dispersion relations for certain low-lying states of the one-dimensional Heisenberg ferromagnet. These states are bound complexes of $M$ overturned spins, and in fact are the states with the lowest energy for given values of the total spin, $z$ component of spin and momentum.

102 citations


Journal ArticleDOI
TL;DR: In this paper, the static structure factor in the two-dimensional spinS = 1/2 square-lattice Heisenberg antiferromagnet Sr2CuO2Cl2 was investigated.
Abstract: We have carried out a neutron scattering investigation of the static structure factorS(q 2D ) (q 2D is the in-plane wave vector) in the two-dimensional spinS=1/2 square-lattice Heisenberg antiferromagnet Sr2CuO2Cl2. For the spin correlation length ξ we find quantitative agreement with Monte Carlo results over a wide range of temperature. The combined Sr2CuO2Cl2-Monte Carlo data, which cover the length scale from ≈1 to 200 lattice constants, are predicted without adjustable parameteres by renormalized classical theory for the quantum nonlinear sigma model. For the structure factor peakS(0), on the other hand, we findS(0)∼ξ 2 for the reduced temperature range 0.16

100 citations


Journal ArticleDOI
24 Mar 1995-Science
TL;DR: The temperature evolution of the internal magnetic field below the freezing temperature mirrors that of the saturation magnetization, closely following the behavior expected for collective spin wave (magnon) excitations.
Abstract: The zero-field muon spin relaxation technique has been used in the direct observation of spontaneous magnetic order below a Curie temperature (T(c)) of approximately 16.1 kelvin in the fullerene charge-transfer salt (tetrakisdimethylaminoethylene)C(60) [(TDAE)C(60)]. Coherent ordering of the electronic magnetic moments leads to a local field of 68(1) gauss at the muon site at 3.2 kelvin (parentheses indicate the error in the last digit). Substantial spatially inhomogeneous effects are manifested in the distribution of the local fields, whose width amounts to 48(2) gauss at the same temperature. The temperature evolution of the internal magnetic field below the freezing temperature mirrors that of the saturation magnetization, closely following the behavior expected for collective spin wave (magnon) excitations. The transition to a ferromagnetic state with a T(c) higher than that of any other organic material is now authenticated.

85 citations


Journal ArticleDOI
TL;DR: In this article, the magnetic properties of diluted mixed Ising ferrimagnetic systems consisting of spin-1/2 and spin- 1 are investigated within the framework of an effective field theory with correlations.
Abstract: The magnetic properties of diluted mixed Ising ferrimagnetic systems consisting of spin-1/2 and spin-1 are investigated within the framework of an effective-field theory with correlations. Particular emphasis is given to the honeycomb lattice with coordination number z=3 for which the phase diagram (transition temperature and compensation temperature) and magnetizations (total and sublattice) are obtained. We find a number of interesting phenomena in these quantities, such as the possibility of two compensation points in the total magnetization curve and magnetization curves not predicted in the N\'eel theory.

77 citations


Journal ArticleDOI
TL;DR: A nearest-neighbor effective Hamiltonian is derived, which takes account of the mixing of higher Co + ion crystal-field levels in a self-consistent manner and is found to be in quantitative agreement with experiment.
Abstract: The lowest-lying excited states in the S= 2 one-dimensional Ising-like antiferromagnet CsCoC13 consist of domain-wall (soliton) pair states. Although the dynamical response function S(g, to) has been calculated for these states, it has not proved possible to explain the results of neutron scattering and Raman experiments without recourse to the introduction of extra terms in the spin Hamiltonian. We argue against the two modifications to the Hamiltonian of CsCoC13 proposed in previous papers, a staggered field term arising from a mean field approach to exchange mixing, and next-nearest-neighbor intrachain coupling, as being unphysical. Instead we derive a nearest-neighbor effective Hamiltonian, which takes account of the mixing of higher Co + ion crystal-field levels in a self-consistent manner. We also present a high-resolution inelastic neutron scattering experiment on CsCoC13, which has allowed the dispersion of the excited states across the Brillouin zone to be studied more carefully than before. These results give a direct measure of S(g, to) in the onedimensional phase where there is a continuum of excited states, and in the three-dimensionally ordered phases, where weak interchain interactions split the continuum into a "Zeeman ladder" of discrete states. The predictions of our theory are found to be in quantitative agreement with experiment.

58 citations



Journal ArticleDOI
TL;DR: In this paper, the authors investigated intrinsic localized spin modes in chains of classical spins coupled ferromagnetically by nearest-neighbor exchange interactions and found that the degree of localization increases as the ratio of the anisotropy constant A to the exchange constant J increases.
Abstract: Intrinsic localized spin modes have been investigated in chains of classical spins coupled ferromagnetically by nearest-neighbor exchange interactions. For this case no localized modes are found. If on-site anisotropy of sufficient magnitude is included, however, localized spin modes appear. The degree of localization increases as the ratio of the anisotropy constant A to the exchange constant J increases. Modes of both even and odd parity occur. The degree of localization also increases if the maximum spin deviation increases with A/J held fixed. The results are applied to the specific case of ${\mathrm{CsFeCl}}_{3}$. Possibilities for the observation of intrinsic localized spin modes are discussed.

Journal ArticleDOI
TL;DR: The results show that the resonator Nyquist noise does not play any role in starting spin superradiance, but the emergence of the latter is initiated by local spin fluctuations due to nonsecular dipole interactions.
Abstract: The question addressed here is: What originates pure spin superradiance in a polarized spin system placed inside a resonantor? The term ``pure'' means that no initial coherence is imposed on spins, and its appearance manifests a purely self-organized collective effect. An accurate solution of evolution equations for a microscopic model is given. The results show that the resonator Nyquist noise does not play any role in starting spin superradiance, but the emergence of the latter is initiated by local spin fluctuations due to nonsecular dipole interactions.

BookDOI
01 Aug 1995
TL;DR: In this article, Chen et al. studied the effect of size effects in the acceleration of spin wave envelope solitons in magnetic films and showed that the size effects can influence the nonlinearity of the spin wave propagation process.
Abstract: Part 1: Linear Microwave Processes in Magnetic Materials: Ferromagnetic Resonance in Magnetic Insulators (P Kabos & C E Patton) Submilimeter Spectroscopy of Antiferromagnetic Dielectrics. Rare Earth Orthoferrites (A M Balbashov et al) Magnetic Ordering in Amorphous Insulators (G Srinivasan) Ferromagnetic Resonance Studies in Metallic Multilayers (R Krishnan & S Prasad) Propagation and Interaction of Magnetostatic Waves in Planar Magnetic Structures with Non-Stationary Parameters (Yu Fetisov) Spectrum of Microwave Spin Waves in Magnetic Multilayers (B A Kalinikos & P A Kolodin) Excitation of Propagating Spin Waves in Magnetic Films and Layered Structures (B A Kalinikos et al). Part 2: Nonlinear Microwave Processes in Magnetic Materials: Size Effects in Parametric Excitation of Spin Waves in Ferrites (V B Cherepanov & A N Slavin) Multistability and Temperature-Induced Nonlinearity of Parametrically Excited Spin Waves (H Benner & G Wiese) Experimental Observation of "Bright" and "Dark" Spin Wave Envelope Solitons in Magnetic Films (M Chen et al) Part 3: Interaction of Microwave Spin Waves with Light: Collinear Interaction of Optical Guided Modes with Microwave Spin Waves in Magnetic Films (D D Stancil) Brillouin Light Scattering from Dipole-Exchange Microwave Spin Waves in Magnetic Films (I V Rojdestvensky et al) Photothermal Characterization of Microwave Magnetic Excitations in Ferrites (J Pelzl & 0 von Gelsau).

Journal ArticleDOI
TL;DR: In this article, the experimental results on two-dimensional nuclear magnetic systems obtained by physical adsorption of 3He atoms on solid substrates are reviewed and discussed in the context of the experimental investigations of adsorbed 3He films.
Abstract: We review in this paper the experimental results on two-dimensional nuclear magnetic systems obtained by physical adsorption of 3He atoms on solid substrates. Two-dimensional nuclear antiferromagnets and ferromagnets have been observed and studied in recent years, providing useful model systems for spin 1/2 magnetic Hamiltonians and leading to results of general validity on the magnetic ordering of two-dimensional spin systems. Heisenberg, multiple spin and Rudermann-Kittel exchange as well as vacancy-induced magnetism are discussed in the context of the experimental investigations of adsorbed 3He films.

Journal ArticleDOI
TL;DR: In this paper, a method is presented to calculate ab initio exchange constants and spin-wave excitations of multi-sublattice magnetic structures on the basis of total-energy calculations of incommensurate magnetic structures.
Abstract: A method is presented to calculate ab initio exchange constants and spin-wave excitations of multi-sublattice magnetic structures on the basis of total-energy calculations of incommensurate magnetic structures. Here the exchange energies, dispersion curves and Curie temperature for magnetite (Fe3O4) are obtained and compared with experimental results.

Journal ArticleDOI
TL;DR: After estimating the spin-relaxation rates due to magnetic impurity and spin-orbit scattering, an explicit experimental geometry for demonstration of spin-charge separation is discussed and may be able to directly demonstrate spin-charges separation in a superconductor using spin injection techniques.
Abstract: The nonequilibrium spin imbalance created when electrons tunnel from a ferromagnet to a superconductor is calculated. Since the charge current in a superconductor is carried by the condensate within a penetration length of the surface and the spin current, which is carried by quasiparticles, can exist in the bulk, one may be able to directly demonstrate spin-charge separation in a superconductor using spin injection techniques. After estimating the spin-relaxation rates due to magnetic impurity and spin-orbit scattering, an explicit experimental geometry for demonstration of spin-charge separation is discussed.


Journal ArticleDOI
TL;DR: Using a recently developed method for calculating series expansions of the excitation spectra of quantum lattice models, the spin-wave spectra for square lattice, S=1/2 Heisenberg-Ising antiferromagnets are obtained.
Abstract: Using a recently developed method for calculating series expansions of the excitation spectra of quantum lattice models, we obtain the spin-wave spectra for square lattice, S=1/2 Heisenberg-Ising antiferromagnets. The calculated spin-wave spectrum for the Heisenberg model is close to but noticeably different from a uniformly renormalized classical (large-S) spectrum with the renormalization for the spin-wave velocity of approximately 1.18. The relative weights of the single-magnon and multiple-magnon contributions to neutron-scattering spectra are obtained for wave vectors throughout the Brillouin zone.

Journal ArticleDOI
TL;DR: In this article, the effects of the small ferromagnetic coupling between chains on the dynamical behavior of the spins in ${\mathrm{KCuF}}_{3}$ were investigated.
Abstract: The effects of the small ferromagnetic coupling between chains on the dynamical behavior of the spins in ${\mathrm{KCuF}}_{3}$ are investigated. Inelastic neutron-scattering measurements of the magnetic excitations in ${\mathrm{KCuF}}_{3}$ were made using a triple-axis spectrometer. The scattering was studied at a number of temperatures; measurements below ${\mathit{T}}_{\mathit{N}}$=39.07\ifmmode\pm\else\textpm\fi{}0.02 K showed well-defined spin waves for energies less than the interchain zone-boundary energy of 11.5 meV. At higher energies a continuum of scattering was observed. The measurements are compared with spin-wave theory, and the field theory used in the preceding paper (paper I). At a temperature of 9 K the scattering at energy transfers of 25 meV and below are in excellent agreement with spin-wave theory when two-magnon processes are included. Above the N\'eel ordering temperature the measurements are compared with field theory. Although this qualitatively describes the temperature behavior of the line shapes it does not account for the observed change in intensity with temperature. This discrepancy is explained by residual interchain correlations.

Journal ArticleDOI
TL;DR: In this article, the theory and simulation of spin-wave soliton formation in thin ferromagnetic films is considered and the necessary and sufficient conditions for soliton creation are analyzed.

Journal ArticleDOI
TL;DR: In this article, a renormalization group approach in a small field approximation is formulated and studied, with a goal to prove the so-called "spin wave picture" displaying massless behavior of the models.
Abstract: A class of low temperature lattice classical spin models with a symmetry groupO(N) is considered, including the classical Heisenberg model. In this paper a renormalization group approach in a small field approximation is formulated and studied, with a goal to prove the so-called “spin wave picture” displaying massless behavior of the models.

Journal ArticleDOI
TL;DR: In this paper, the authors apply a model for SU(3) breaking to the analysis of the spin contents of the nucleon from the latest data on first moments of spin dependent structure functions and include higher order QCD corrections.

Journal ArticleDOI
TL;DR: In this article, the spin-Peierls gap was studied by means of neutron inelastic scattering and the splitting of the single gap state into three distinct excitation branches under a magnetic field can be regarded as direct evidence for the singlet-triplet transition in a spin-peierls system.
Abstract: The magnetic field dependence of the spin-Peierls gap in CuGe${\mathrm{O}}_{3}$ has been studied by means of neutron inelastic scattering. The splitting of the single gap state into three distinct excitation branches under a magnetic field can be regarded as direct evidence for the singlet-triplet transition in a spin-Peierls system.

Journal ArticleDOI
TL;DR: Finite-temperature spin dynamics in planar t-J model is studied using the method based on the Lanczos diagonalization of small systems, supporting a scenario related to the marginal Fermi-liquid one for the explanation of neutron-scattering and NMR-relaxation experiments in cuprates.
Abstract: Finite-temperature spin dynamics in the planar $t\ensuremath{-}J$ model are studied using a method based on the Lanczos diagonalization of small systems. The dynamical spin structure factor at moderate dopings shows the coexistence of free-fermion-like and spin-fluctuation time scales. At $TlJ$, low-frequency and static susceptibilities show a pronounced $T$ dependence, supporting a scenario related to the marginal Fermi liquid one, for the explanation of neutron-scattering and NMR relaxation experiments in cuprates. Calculated NMR relaxation rates reasonably reproduce experimental ones.

Journal ArticleDOI
TL;DR: In this article, both theoretical and experimental results concerning the zero-field microwave absorption related to the two modes of domain mode ferromagnetic resonance (DM-FMR) which occur in unsaturated garnet films supporting parallel stripe domains are reported.

Journal ArticleDOI
TL;DR: In this article, the long-range order in two-dimensional isotropic dipolar Heisenberg antiferromagnets on a honeycomb lattice is studied, yielding via linear spin-wave theory a non vanishing order parameter at finite temperatures.

Journal ArticleDOI
TL;DR: In this article, the spin wave stiffness in the giant magnetoresistance material La 0.67 Ba 0.33 MnO 3 was measured by observing standing spin wave resonances in about 100 nm thick films.


Journal ArticleDOI
TL;DR: In this article, the static and dynamic spin fluctuations in the spinS=1, two-dimensional (2D) square-lattice antiferromagnet La2NiO4 have been studied over a wide temperature range using neutron scattering techniques.
Abstract: The static and dynamic spin fluctuations in the spinS=1, two-dimensional (2D) square-lattice antiferromagnet La2NiO4 have been studied over a wide temperature range using neutron scattering techniques. The spin correlations in La2NiO4 exhibit a crossover from two- to three-dimensional (3D) behavior as the Neel temperature is approached from above. Critical slowing down of the low-energy spin fluctuations is also observed just aboveTN. The correlation length, ξ(T), and the static structure factor,S(0), have been measured and are compared with recent theoretical calculations for the quantum 2D Heisenberg antiferromagnet using microscopic parameters determined from previous spin-wave measurements. Good agreement for ξ(T) is found with the exact low-temperature result of Hasenfratz and Niedermeyer provided that 2πps is renormalized by ≈20% from the spin-wave value.

Journal ArticleDOI
TL;DR: The spin-1/2 frustrated Heisenberg model is investigated using a block-spin perturbation approach on kagome$aai\char22{} and triangular lattices and it is seen that chiral-ordered variational states have high energies compared to the other variationalStates.
Abstract: The spin-1/2 frustrated Heisenberg model (HM) is investigated using a block-spin perturbation approach on kagome$aai\char22{} and triangular lattices. In both cases, after coarse graining the triangles on the original lattice and truncation of the Hilbert space to the triangular ground-state subspace, HM reduces to an effective model on a triangular lattice in terms of the triangular-block degrees of freedom, viz. the spin and the chirality quantum numbers. The chirality part of the effective Hamiltonian captures the essential difference between the two lattices. It is seen that chiral-ordered variational states have high energies compared to the other variational states.