Showing papers on "Spin wave published in 2001"
TL;DR: The observed dispersion relation shows evidence for substantial interactions beyond the nearest-neighbor Heisenberg term which can be understood in terms of a cyclic or ring exchange due to the strong hybridization path around the Cu4O4 square plaquettes.
Abstract: The magnetic excitations of the square-lattice spin-1/2 antiferromagnet and high- T(c) parent compound La2CuO4 are determined using high-resolution inelastic neutron scattering. Sharp spin waves with absolute intensities in agreement with theory including quantum corrections are found throughout the Brillouin zone. The observed dispersion relation shows evidence for substantial interactions beyond the nearest-neighbor Heisenberg term which can be understood in terms of a cyclic or ring exchange due to the strong hybridization path around the Cu4O4 square plaquettes.
482 citations
TL;DR: In this article, a review is devoted to both the experimental and theoretical aspects of lateral converse effects observed for spin waves, with the wave vector in the 10-10 cm range, where the magnetic dipole interaction plays the most important role.
452 citations
TL;DR: In this paper, Heisenberg exchange parameters for bcc Fe, fcc Co, and fcc Ni were calculated using the nonrelativistic spin-polarized Green-function technique within the tight-binding linear muffin-tin orbital method and by employing the magnetic force theorem to calculate total energy changes associated with a local rotation of magnetization directions.
Abstract: We have calculated Heisenberg exchange parameters for bcc Fe, fcc Co, and fcc Ni using the nonrelativistic spin-polarized Green-function technique within the tight-binding linear muffin-tin orbital method and by employing the magnetic force theorem to calculate total energy changes associated with a local rotation of magnetization directions. We have also determined spin-wave stiffness constants and found the dispersion curves for metals in question employing the Fourier transform of calculated Heisenberg exchange parameters. Detailed analysis of convergence properties of the underlying lattice sums was carried out and a regularization procedure for calculation of the spin-wave stiffness constant was suggested. Curie temperatures were calculated both in the mean-field approximation and within the Green-function random-phase approximation. The latter results were found to be in a better agreement with available experimental data.
418 citations
TL;DR: In this paper, the propagation of spin waves through a periodic multilayered magnetic structure is analyzed, where it is assumed that the structure consists of ferromagnetic layers having the same thickness but different magnetizations.
290 citations
TL;DR: The Berry phase due to the spin wave function gives rise to the orbital ferromagnetism and anomalous Hall effect in the noncoplanar antiferromagnetic ordered state on face-centered-cubic lattice once the crystal is distorted perpendicular to the ( 1,1,1) or (1, 1,0) plane.
Abstract: The Berry phase due to the spin wave function gives rise to the orbital ferromagnetism and anomalous Hall effect in the noncoplanar antiferromagnetic ordered state on face-centered-cubic (fcc) lattice once the crystal is distorted perpendicular to the $(1,1,1)$ or $(1,1,0)$ plane. The relevance to the real systems $\ensuremath{\gamma}$-FeMn and ${\mathrm{NiS}}_{2}$ is also discussed.
229 citations
TL;DR: In this article, the thermal conductivity of the quasi-one-dimensional spin-chain compound for cuprates with copper-oxygen chains and strong intrachain interactions was investigated.
Abstract: We present the results of measurements of the thermal conductivity of the quasi-one-dimensional $S=1/2$ spin-chain compound ${\mathrm{SrCuO}}_{2}$ in the temperature range between 04 and 300 K along the directions parallel and perpendicular to the chains An anomalously enhanced thermal conductivity is observed along the chains above about 40 K The analysis of the present data and a comparison with analogous recent results for ${\mathrm{Sr}}_{2}{\mathrm{CuO}}_{3}$ and other similar materials demonstrates that this behavior is generic for cuprates with copper-oxygen chains and strong intrachain interactions The observed anomalies are attributed to the one-dimensional energy transport by spin excitations (spinons), limited by the interaction between spin and lattice excitations The energy transport along the spin chains has a nondiffusive character, in agreement with theoretical predictions for integrable models
199 citations
TL;DR: Experimental evidence for orbitons is reported in LaMnO3, using Raman scattering measurements and a model calculation of orbiton resonances which provides a good fit to the experimental data is performed.
Abstract: A basic concept in solid-state physics is that when some kind of symmetry in a solid is spontaneously broken, collective excitations will arise1. For example, phonons are the collective excitations corresponding to lattice vibrations in a crystal, and magnons correspond to spin waves in a magnetically ordered compound. Modulations in the relative shape of the electronic clouds in an orbitally ordered state2,3,4,5,6,7,8,9 could in principle give rise to orbital waves, or ‘orbitons’, but this type of elementary excitation has yet to be observed experimentally. Systems in which the electrons are strongly correlated—such as high-temperature superconductors and manganites exhibiting colossal magnetoresistivity—are promising candidates for supporting orbital waves, because they contain transition-metal ions in which the orbital degree of freedom is important10,11. Orbitally ordered states have been found in several transition-metal compounds12,13, and orbitons have been predicted theoretically for LaMnO3 (refs 4, 5). Here we report experimental evidence for orbitons in LaMnO3, using Raman scattering measurements. We perform a model calculation of orbiton resonances which provides a good fit to the experimental data.
166 citations
TL;DR: In this article, the authors describe the evolution of the static and dynamic spin correlations of the system with respect to the canted magnetic state towards the insulating ferromagnetic state, approaching the metallic transition.
Abstract: We describe the evolution of the static and dynamic spin correlations of ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{MnO}}_{3}$ for $x=0.1,$ 0.125, and 0.2, where the system evolves from the canted magnetic state towards the insulating ferromagnetic state, approaching the metallic transition $(x=0.22).$ In the $x=0.1$ sample, the observation of two spin-wave branches typical of two distinct types of magnetic coupling and of a modulation in the elastic diffuse-scattering characteristic of ferromagnetic inhomogeneities confirms the static and dynamic inhomogeneous features previously observed at $xl0.1.$ The anisotropic q dependence of the intensity of the low-energy spin wave suggests a bidimensional character for the static inhomogeneities. At $x=0.125,$ which corresponds to the occurrence of a ferromagnetic and insulating state, one spin wave branch, anisotropic, is detected. At this concentration, an anomaly appears at ${\mathbf{q}}_{0}=(1.25,1.25,0).$ At $x=0.2,$ the spin-wave branch appears as isotropic. In addition to the anomaly observed at ${q}_{0},$ extra magnetic excitations are observed at larger q, forming an optical branch.
136 citations
TL;DR: In this article, the magnetic properties of nonstoichiometric cobalt ferrite nanocrystals differing by their sizes were investigated by magnetic measurements and 57Fe Mossbauer spectroscopy.
Abstract: The magnetic properties of nonstoichiometric cobalt ferrite nanocrystals differing by their sizes were investigated by magnetic measurements and 57Fe Mossbauer spectroscopy. We found that the spin-wave Bloch exponent increases with increasing particle size, in agreement with previous studies. Under a magnetic field of 7 T, we observed that the partial reorientation of the two ferrimagnetic Fe3+ sublattice magnetizations towards the field direction increases with increasing the particle size; we discuss the applicability of an intrinsic spin canting model as a function of the particle size. An evaluation of the relative amounts of cobalt and iron in each spinel site is given.
123 citations
TL;DR: In this article, the propagating spin wave spectroscopy (PSWS) technique is applied for the first time to metallic thin film patterns, allowing to measure their magnetostatic wave modes.
Abstract: The propagating spin wave spectroscopy (PSWS) technique is applied for the first time to metallic thin film patterns, allowing to measure their magnetostatic wave modes. Using micrometer scale local excitation and detection, we show that magnetostatic surface waves propagate on a distance as long as 40 μm in a continuous permalloy film. In micrometer wide permalloy stripes, we observe both quantized spin wave modes and quasi-saturation modes, well explained by existing models. In addition, low-frequency additional modes were observed which, we suggest, are generated in the magnetically inhomogeneous edge regions.
116 citations
Book•
02 Jan 2001
TL;DR: In this article, Paramagnetism Interacting Spins Mean Field Approximation Spin Waves Green's Functions Methods Dipole-Dipole Interactions Itinerant Magnetism Indirect Exchange Magnetic Impurities Low Dimensions Surface Magnetism Two-Magnon Eigenstates Other Interactions Coherant Magnon States Appendices: Group Theory Time Reversal.
Abstract: Contents: Paramagnetism Interacting Spins Mean Field Approximation Spin Waves Green's Functions Methods Dipole-Dipole Interactions Itinerant Magnetism Indirect Exchange Magnetic Impurities Low Dimensions Surface Magnetism Two-Magnon Eigenstates Other Interactions Coherant Magnon States Appendices: Group Theory Time Reversal.
TL;DR: In this article, the authors developed the theory of exchange/dipole spin wave excitations of ferromagnetic nanowires of cylindrical cross section, where the magnetization is parallel to the axis of the wire.
Abstract: We develop the theory of exchange/dipole spin wave excitations of ferromagnetic nanowires of cylindrical cross section, where the magnetization is parallel to the axis of the wire In addition, we provide the theory of the microwave response of such structures, for the case where the nanowire is also a conductor We present explicit calculations of both the mode structure of nanowires, and also their ferromagnetic resonance spectrum, with attention to recent experimental studies We compare differences between the physical picture appropriate for the cylinder, with the well studied case of the ferromagnetic film
TL;DR: In this paper, the authors investigated the spin-wave damping in ferromagnetic (FM)/antiferromagnetic bilayers exhibiting exchange bias and found that the measured linewidths are more than one order of magnitude larger than in similar NiFe films without exchange bias.
Abstract: Ferromagnetic resonance and Brillouin light-scattering techniques have been used to investigate the spin-wave damping in ferromagnetic (FM)/antiferromagnetic bilayers exhibiting exchange bias. The measurements were done in the prototype system NiFe/NiO sputtered on Si(100) as a function of the NiFe film thickness. The linewidths measured with both techniques are more than one order of magnitude larger than in similar NiFe films without exchange bias and increase dramatically with decreasing FM film thickness. The data are consistently explained by a relaxation mechanism based on two-magnon scattering processes due to the local fluctuation of the exchange coupling caused by interface roughness. The local interface energy necessary to account for the measured linewidths is on the same order of the atomic exchange coupling.
TL;DR: In this paper, a microscopic theory of the long-wavelength magnetic properties of the ferromagnetic diluted magnetic semiconductor (Ga,Mn)As is presented, where the host semiconductor band structure is described by a six-band Kohn-Luttinger Hamiltonian.
Abstract: We present a microscopic theory of the long-wavelength magnetic properties of the ferromagnetic diluted magnetic semiconductor (Ga,Mn)As. Details of the host semiconductor band structure, described by a six-band Kohn-Luttinger Hamiltonian, are taken into account. We relate our quantum-mechanical calculation to the classical micromagnetic energy functional and determine anisotropy energies and exchange constants. We find that the exchange constant is substantially enhanced compared to the case of a parabolic heavy-hole-band model.
TL;DR: The equation of motion for the spin degrees of freedom within time-dependent spin-density-functional theory (TD-SDFT) is derived and a prescription for obtaining many-body corrections to the single-particle spin currents from the Kohn-Sham equation is obtained.
Abstract: We derive and analyze the equation of motion for the spin degrees of freedom within time-dependent spin-density-functional theory (TD-SDFT). The results are (i) a prescription for obtaining many-body corrections to the single-particle spin currents from the Kohn-Sham equation of TD-SDFT, (ii) the existence of an exchange-correlation (xc) torque within TD-SDFT, (iii) a prescription for calculating, from TD-SDFT, the torque exerted by spin currents on the spin magnetization, (iv) a novel exact constraint on approximate xc functionals, and (v) the discovery of serious deficiencies of popular approximations to TD-SDFT when applied to spin dynamics.
TL;DR: It is shown that the low energy spin dynamics in the system can be mapped into an o(n) nonlinear sigma model and consequences of the discrete symmetry are explored and some measurements are proposed to probe it.
Abstract: We study spin correlations in Bose-Einstein condensates of spin 1 bosons with scatterings dominated by a total spin equal 2 channel We show that the low energy spin dynamics in the system can be mapped into an o(n) nonlinear sigma model n = 3 at the zero magnetic field limit and n = 2 in the presence of weak magnetic fields In an ordered phase, the ground state has a discrete Z2 symmetry and is degenerate under the group [U(1)xS(n-1)]/Z(2) We explore consequences of the discrete symmetry and propose some measurements to probe it
TL;DR: In this article, the effect of spin-wave mode on the transverse spin fluctuation amplitude is examined, and it is shown that this effect is crucial for proper theoretical description of magnetic behaviours in the ordered state.
Abstract: On the basis of the spin fluctuation mechanism, magnetic properties of itinerant-electron weak ferromagnets are discussed, for the wide temperature range from the ground state to the paramagnetic state, explicitly taking into account the effects of zero-point quantum spin fluctuations. Particular attention is focused on properties of the ordered phase. The temperature dependence of the spontaneous magnetic moment, for instance, is quantitatively analysed in close comparison with experiments. It is also shown that the fourth-order expansion coefficient of the free energy in powers of the static magnetic moment is temperature dependent, and therefore magnetic isotherms are not so simple as was originally anticipated in the Stoner–Wohlfarth theory. We explicitly examine the effect of the spin-wave mode on the transverse spin fluctuation amplitude, and show that this effect is crucial for the proper theoretical description of magnetic behaviours in the ordered state.
TL;DR: In this article, an approximate ground state wave function was proposed for the two-layer square lattice quantum antiferromagnet with spins 1 and 2, which consistently covers all phases by means of a unitary transformation.
Abstract: The two-layer square lattice quantum antiferromagnet with spins 1
2 shows a zero-field magnetic order-disorder transition at a critical ratio of the inter-plane to intra-plane couplings. Adding a uniform magnetic field tunes the system to canted antiferromagnetism and eventually to a fully polarized state; similar behavior occurs for ferromagnetic intra-plane coupling. Based on a bond operator spin representation, we propose an approximate ground state wavefunction which consistently covers all phases by means of a unitary transformation. The excitations can be efficiently described as independent bosons; in the antiferromagnetic phase these reduce to the well-known spin waves, whereas they describe gapped spin-1 excitations in the singlet phase. We compute the spectra of these excitations as well as the magnetizations throughout the whole phase diagram.
TL;DR: In this article, the authors discuss a different kind of spin current, associated with expansion and contraction of the Fermi surfaces, which is more nonlocal in nature, and may exist even in locations where the electrical current density is zero.
Abstract: In metallic ferromagnets, an electric current is accompanied by a flux of angular momentum, also called spin current. In multilayers, spatial variations of the spin current correspond to drive torques exerted on a magnetic layer. These torques result in spin precession above a certain current threshold. The usual kind of spin current is associated with translation of the spin-up and spin-down Fermi surfaces in momentum space. We discuss a different kind of spin current, associated with expansion and contraction of the Fermi surfaces. It is more nonlocal in nature, and may exist even in locations where the electrical current density is zero. It is larger than the usual spin current, in a ratio of 10 or 100, at least in the case of one-dimensional current flow. The new spin current is proportional to the difference Δμ≃10−3 eV between spin-up and spin-down Fermi levels, averaged over the entire Fermi surface. Conduction processes, spin relaxation, and spin-wave emission in the multilayer can be described by an equivalent electrical circuit resembling an unbalanced dc Wheatstone bridge. And Δμ corresponds to the output voltage of the bridge.
TL;DR: The spin pair-correlation function of finite bipartite antiferromagnetic Heisenberg quantum spin rings was studied numerically by means of exact diagonalization techniques as mentioned in this paper.
Abstract: The spin pair-correlation function of finite bipartite antiferromagnetic Heisenberg quantum spin rings was studied numerically by means of exact diagonalization techniques. For large spins, the spectrum of the spin pair-correlation function is of a remarkably simple structure: It consists of few characteristic peaks at low, and a broad featureless signal at high temperatures. This arises as the energy spectrum exhibits a set of parallel rotational bands at low energies emerging into a quasi-continuum of states, with transitions from the lowest rotational hand to the quasi-continuum being highly suppressed. The energies of the rotational hands can be accurately described by a generalized dispersion relation that depends on the total spin quantum number and, as usual, on the shift quantum number. These regularities are better fulfilled the larger the spin length but the smaller the ring size. It will he shown that all these features are associated with the underlying sublattice structure of the spin rings, and it is argued that they are valid for a more general class of finite Heisenberg systems than rings.
TL;DR: In this article, the authors show that the presence of sharp interfaces causes a local increase of the interaction between spin waves and conduction electrons, which leads to an increase in the Gilbert spin-damping parameter near an interface.
Abstract: In magnetic multilayers, the presence of sharp interfaces causes a local increase of the interaction between spin waves and conduction electrons. This leads to an increase of the Gilbert spin-damping parameter near an interface. In turn, the ferromagnetic-resonance linewidth is increased over its value in single-layer films. In addition, the precession of magnetic spins during ferromagnetic resonance induces conduction-electron transitions from the spin-up to the spin-down band. As a result, the spin-up Fermi level differs from the spin-down Fermi level by an amount Δμ. At high precession amplitudes, the existence of Δμ causes a measurable decrease of the Gilbert parameter. At precession-cone angles exceeding 4°, the Gilbert parameter returns nearly to its single-layer value. Ferromagnetic-resonance line shapes are predicted to be non-Lorentzian, narrower and sharper near the top. This line-narrowing effect increases with increasing microwave power. The effect of Δμ spreads into the entire multilayer, so that precession in one magnetic layer can cause a reduction or increase of the Gilbert parameter in other layers, or even a spontaneous spin precession in these layers.
TL;DR: In this article, the authors use theoretical estimates of spin-wave energies and Monte Carlo simulations to demonstrate that longwavelength collective fluctuations, neglected by mean-field theory, will limit the critical temperature in large density-of-states materials.
Abstract: Mean-field-theory predicts that the Curie temperature Tc of a (III,Mn)V ferromagnet will be proportional to the valence band density-of-states of its host (III,V) semiconductor, suggesting a route toward room-temperature ferromagnetism in this materials class. In this letter, we use theoretical estimates of spin-wave energies and Monte Carlo simulations to demonstrate that long-wavelength collective fluctuations, neglected by mean-field theory, will limit the critical temperature in large density-of-states materials. We discuss implications for high Tc searches.
TL;DR: In this paper, the spin-orbit coupling induces frustrating Ising-like anisotropy terms in the spin Hamiltonian, which invalidate noninteracting spin-wave theory.
Abstract: A theory of the anisotropic superexchange and low-energy spin excitations in a Mott insulator with ${t}_{2g}$ orbital degeneracy is presented. We observe that the spin-orbit coupling induces frustrating Ising-like anisotropy terms in the spin Hamiltonian, which invalidate noninteracting spin-wave theory. The frustration of classical states is resolved by an order from disorder mechanism, which selects a particular direction of the staggered moment and generates a quantum spin gap. The theory explains well the observed magnon gaps in ${\mathrm{LaTiO}}_{3}.$ As a test case, a specific prediction is made on the splitting of magnon branches at certain momentum directions.
TL;DR: In this article, the spin wave spectra in layered composite materials are computed by means of a transfer matrix method with evidence for the existence of numerous frequency gaps, and essential properties of these spectra are successfully explained within the framework of approximate models of independent films or an effective medium, according to the strength of the magnetization and exchange contrasts.
TL;DR: In this article, the thermodynamic properties and spin dynamics of a class of magnetic rings closely related to ferric wheels, antiferromagnetic ring systems, in which one of the Fe (III) ions has been replaced by a dopant ion to create an excess spin.
Abstract: We study theoretically the thermodynamic properties and spin dynamics of a class of magnetic rings closely related to ferric wheels, antiferromagnetic ring systems, in which one of the Fe (III) ions has been replaced by a dopant ion to create an excess spin. Using a coherent-state spin path integral formalism, we derive an effective action for the system in the presence of a magnetic field. We calculate the functional dependence of the magnetization and tunnel splitting on the magnetic field and show that the parameters of the spin Hamiltonian can be inferred from the magnetization curve. We study the spin dynamics in these systems and show that quantum tunneling of the N\'eel vector also results in tunneling of the total magnetization. Hence, the spin correlation function shows a signature of N\'eel vector tunneling, and electron spin resonance (ESR) techniques or ac susceptibility measurements can be used to measure both the tunneling and the decoherence rate. We compare our results with exact diagonalization studies on small ring systems. Our results can be easily generalized to a wide class of nanomagnets, such as ferritin.
TL;DR: In this article, two powerful methods for the ab initio calculation of adiabatic spin-wave spectra are introduced, a frozen-magnon-torque method for systems with large exchange fields and a transverse-susceptibility method which may be used also for materials with smaller exchange fields.
Abstract: The interpretation of the physics of magnets with reduced dimensionality often requires information on the spin wave excitations at arbitrary wavelengths which is generally hard to obtain experimentally. Two powerful methods for the ab initio calculation of adiabatic spin-wave spectra are introduced, a frozen-magnon-torque method for systems with large exchange fields and a transverse-susceptibility method which may be used also for materials with smaller exchange fields. The efficiency of both methods results from the fact that the number of calculations required to obtain the spin-wave spectrum scales linearly with the number of basis atoms in the unit cell. Results are given for Fe, Co, Ni, permalloy ${\mathrm{Ni}}_{3}\mathrm{Fe},$ and CoFe, materials which are often used for thin-film technologies.
TL;DR: In this paper, exchange coupled Landau-Lifshitz equations for the local magnetization and the spin-polarized charge carriers are combined with transport equations for charge and spin currents.
Abstract: Spin currents injected into magnetic thin films may noticeably change the magnetization of the films. To describe this effect, exchange coupled Landau-Lifshitz equations for the local magnetization and the spin-polarized charge carriers are combined with transport equations for charge and spin currents. For steady state transport one obtains two different instability conditions. Both conditions are supported by recent experimental data on current induced magnetization reversal and spin-wave excitations. No second ferromagnetic layer is needed for excitations due to spin transfer.
TL;DR: An overview of the current status of spin wave excitations in arrays of magnetic dots and wires is given in this article, where both the status of theory and recent inelastic light scattering experiments addressing the most important issues; the quantization of localized spin waves due to the in-plane confinement of spin waves in elements, dipolar coupling between the quantized modes, and the localization of the modes within rectangular elements due to an inhomogeneous demagnetizing field.
Abstract: An overview of the current status of the study of spin wave excitations in arrays of magnetic dots and wires is given. We describe both the status of theory and recent inelastic light scattering experiments addressing the most important issues; the quantization of localized spin waves due to the in-plane confinement of spin waves in elements, dipolar coupling between the quantized modes, and the localization of the modes within rectangular elements due to an inhomogeneous demagnetizing field.
TL;DR: In this paper, an interference ferromagneticnet/semiconductor/ferromagnet transistor is proposed, where the relative conductance difference between parallel and antiparallel magnetization oscillates as a function of gate voltage.
Abstract: An interference ferromagnet/semiconductor/ferromagnet transistor is proposed, where the relative conductance difference between parallel and antiparallel magnetization oscillates as a function of gate voltage. The characteristics of a one-dimensional as well as a two-dimensional structure are calculated and compared. In both cases the interferences result in an enhanced spin signal. It is shown that by using the spin filtering effect of an interface barrier the signal can be further increased.
TL;DR: In this article, the nonlinear spin dynamics of an anisotropic Heisenberg ferromagnetic spin chain with Dzyaloshinskii-Moriya interactions in the semiclassical limit were investigated.
Abstract: We investigate the nonlinear spin dynamics of an anisotropic Heisenberg ferromagnetic spin chain with Dzyaloshinskii-Moriya interactions in the semiclassical limit. We have identified four completely integrable spin models with soliton spin excitations for specific parametric choices and also constructed perturbed solitons. We also obtain solitary spin excitations for a linearly perturbed integrable model at higher order.