Showing papers on "Exchange interaction published in 1992"
TL;DR: In this paper, the static properties of the sphericalp-spin interaction spin glass model are calculated using the replica method and it is shown that within the Parisi scheme the most general solution is the one-step replica symmetry breaking.
Abstract: The static properties of the sphericalp-spin interaction spin glass model are calculated using the replica method. It is shown that within the Parisi scheme the most general solution is the one-step replica symmetry breaking. The transition from the replica symmetric solution to the replica replica symmetry broken one is either continuous or discontinuous inq
1−q0 depending on the strength of the external magnetic field. The model can be solved explicitly for anyp at any temperature and magnetic field. Below the transition we find an infinite number of metastable states.
444 citations
TL;DR: A Ruderman-Kittel approach to the problem of oscillatory exchange coupling between ferromagnetic layers separated by a nonmagnetic metal spacer is presented, valid for arbitrary crystal structure and Fermi surface.
Abstract: We present a Ruderman-Kittel approach to the problem of oscillatory exchange coupling between ferromagnetic layers separated by a nonmagnetic metal spacer. This model provides a very simple explanation for the occurrence of long periods as well as multiperiodic oscillations, and is valid for arbitrary crystal structure and Fermi surface. The role of defects, such as misfit dislocations and interfacial roughness, is discussed.
401 citations
TL;DR: In this paper, the ground state of the alternating spin 1/2 Heisenberg chain with couplings J(> 0) and J′ is studied and the behavior of the string order and energy gap indicates that the ground states over the whole range −∞ ≤ J′< J can be regarded as a single phase.
Abstract: The ground state of the alternating spin 1/2 Heisenberg chain with couplings J(> 0) and J′ is studied. This model interpolates the S=1 and S=1/2 antiferromagnetic Heisenberg chains continuously. The behavior of the string order and energy gap indicates that the ground state over the whole range −∞ ≤ J′< J can be regarded as a single phase. The physical picture of the ground state and the first excited state is also discussed.
198 citations
TL;DR: In this article, a shift hysteresis loop was used to investigate exchange anisotropy in 500 A CoxNi1−xO/300 A Ni81Fe19 polycrystalline bilayer couples.
Abstract: Shifted hysteresis loops were used to investigate exchange anisotropy in 500 A CoxNi1−xO/300 A Ni81Fe19 polycrystalline bilayer couples. Bilayers of Ni81Fe19 with NiO have a room‐temperature exchange field, He, of 30 Oe in the as‐deposited state. A maximum in the exchange field at room temperature was observed near x=0.4, indicating an optimal alloying of the properties of the high anisotropy CoO and the high Neel temperature NiO. The blocking temperatures of the exchange couples vary linearly with x, suggesting a linear dependence of the oxide Neel temperature with x.
192 citations
TL;DR: The first finite-size scaling analysis of the frustrated Heisenberg model in two dimensions was presented in this paper, which indicated a continuous phase transition from the ordered phase into an intermediate phase without long-range magnetic order, as for the (2 + 1)-dimensional nonlinear sigma model.
Abstract: Using results for the 4 × 4 and 6 × 6 lattice, we produce the first finite-size scaling analysis of the frustrated Heisenberg model in two dimensions. The results indicate a continuous phase transition from the ordered phase into an intermediate phase without long-range magnetic order, as for the (2 + 1)-dimensional nonlinear sigma-model. The intermediate phase is stable for 0.4 < J2/J1 < 0.65 and exhibits either dimerization or broken chiral symmetry. The transition to the collinear phase at J2/J1 0.65 is apparently of first order.
129 citations
TL;DR: In this paper, the position of the localized excited state within the energy gap is determined over the whole regime of the magnitude of T K /Δ (T K : Kondo temperature, Δ: superconducting energy gap).
Abstract: A magnetic impurity doped in a superconductor produces a localized excited state within the energy gap. This problem is studied by applying Wilson's numerical renormalization group method. The ground state and the first excited state are traced by changing the exchange coupling constant relative to the energy gap. Thereby the position of the localized excited state within the energy gap is determined over the whole regime of the magnitude of T K /Δ ( T K : Kondo temperature, Δ: superconducting energy gap). A crossing of the lowest doublet and singlet is clearly observed at T K /Δ≃0.3. The ferromagnetic and Ising cases have been studied also. In the ferromagnetic case the localized excited state stays close to the gap edge since the exchange coupling is renormalized to a weak coupling. The case of the Ising-like sd coupling, which is exactly solvable, can be used to check the reliability of the present approach and the effect of the discretization.
127 citations
TL;DR: In this article, the effect of intergrain exchange and magnetostatic interactions on remanence and coercivity was calculated numerically for an isotropic Nd-Fe-B model magnet composed of 8000 grains.
Abstract: The effect of intergrain exchange and magnetostatic interactions on remanence and coercivity is calculated numerically for an isotropic Nd-Fe-B model magnet composed of 8000 grains. The intergrain exchange interaction affects the magnetizing process markedly when the grain size L is small, but the magnetostatic interaction does not have substantial effects. The calculated remanence which takes the intergrain exchange interaction into account increases with decreasing L from Ms/2 (Ms: the saturation magnetization) to Ms and agrees roughly with the experimental results. The calculated coercivity decreases with decreasing L from 0.48HA (HA: the anisotropy field) to 0. Our results suggest that the large remanence above Ms/2 observed experimentally in isotropic Nd-Fe-B magnets can be explained by the intergrain exchange interaction between Nd2Fe14B grains.
119 citations
IBM1
TL;DR: In this article, the metal-insulator transition in orthorhombic perovskites was accompanied by the sudden 3D magnetic ordering of the Ni ions (μNi ≈ 0.9 μB), described by a commensurate κ = (1/2, 0, 1/2) spin density wave.
Abstract: The metal-insulator transition in the orthorhombic perovskites PrNiO3 and NdNiO3 is accompanied by the sudden 3D magnetic ordering of the Ni ions (μNi ≈ 0.9 μB). The magnetic ground state, described by a commensurate κ = (1/2, 0, 1/2) spin density wave, is unprecedented in a perovskite structure. The coexistence of F and AF interactions suggests the existence of an orbital superlattice. This results from the breakdown of the degeneracy of the NiIII (t2g6 eg1) state due to electronic correlations. The gap is probably of charge-transfer type rather than originated by the exchange interactions.
102 citations
TL;DR: In this article, the k.p theory of the band structure of IV-VI compounds is presented, taking into account the narrow energy gaps and strong spin-orbit interactions in the materials.
Abstract: Magneto-optical properties of PbTe and PbSe alloyed with paramagnetic ions Mn and Eu are reviewed. The k.p theory of the band structure of IV-VI compounds is presented, taking into account the narrow energy gaps and strong spin-orbit interactions in the materials. The exchange interaction between the paramagnetic ions and mobile carriers is included in the framework of the mean-field approximation. The experimental data of various authors on magnetization, interband magneto-optics, intraband magneto-optics and four-wave mixing are presented. All results are successfully described by the theory, treating the exchange integrals as adjustable parameters. It is shown that the exchange interaction is of particular importance for the valence bands. Differences between semimagnetic behaviours of Mn-based and Eu-based systems are emphasized as well as those between the IV-VI and II-VI semimagnetic compounds.
85 citations
TL;DR: Exchange enhancements of the spin-polarized 2D electron gas are determined for the first time by inelastic light scattering from spin-flip inter-Landau-level and intersubband excitations.
Abstract: Exchange enhancements of the spin-polarized 2D electron gas are determined for the first time by inelastic light scattering from spin-flip inter-Landau-level and intersubband excitations. In the magnetic quantum limit v=1 the splitting between long wavelength magnetoplasmons and spin-flip inter-Landau-level excitations is a direct spectroscopic measurement of the enhanced exchange energy. At v=1 the enhancements in GaAs quantum wells are in agreement with the Hartree-Fock approximation
79 citations
TL;DR: Angle-resolved photoemission is used to determine the temperature-dependent electronic properties of ferromagnetic bulk Gd along Γ-A of the three-dimensional Brillouin zone.
Abstract: Angle-resolved photoemission is used to determine the temperature-dependent electronic properties of ferromagnetic bulk Gd along Γ-A of the three-dimensional Brillouin zone. The Δ 2 band exchange splitting (0.85 eV) and dispersion (0.5 eV) are in reasonably good agreement with self-consistent local spin-density approximation calculations. The conduction-band magnetic exchange splitting vanishes at the Curie temperature following a conventional power law with a Heisenberg critical exponent
TL;DR: It is shown that generalized gradient approximations for exchange only quite generally can not simultaneously reproduce both the asymptotic forms of the exchange energy density and the exchange potential of finite systems, and it is concluded that GGAs by their very concept are not suited to reproduce these asymPTotic properties of infinite systems.
Abstract: It is shown that generalized gradient approximations (GGAs) for exchange only, due to their very limited form, quite generally can not simultaneously reproduce both the asymptotic forms of the exchange energy density and the exchange potential of finite systems. Furthermore, mechanisms making GGAs formally approach at least one of these asymptotic forms do not improve the corresponding quantity in the relevant part of the asymptotic regime of atoms. By constructing a GGA which leads to superior atomic exchange energies compared to all GGAs heretofore but does not reproduce the asymptotic form of the exact exchange energy density it is demonstrated that this property is not important for obtaining extremely accurate atomic exchange energies. We conclude that GGAs by their very concept are not suited to reproduce these asymptotic properties of finite systems. As a byproduct of our discussion we present a particularly simple and direct proof of the well known asymptotic structure of the exchange potential of finite spherical systems.
TL;DR: The magnetic ordering at the surface of epitaxial Cr overlayers on Fe(100) is studied by spin-polarized electron-energy-loss spectroscopy, proving directly that the surface Cr layer has a net ferromagnetic moment and that successive layers order antiferromagnetically.
Abstract: The magnetic ordering at the surface of epitaxial Cr overlayers on Fe(100) is studied by spin-polarized electron-energy-loss spectroscopy. The exchange asymmetry oscillates with the thickness of the Cr overlayer with a period of about two atomic layers, proving directly that the surface Cr layer has a net ferromagnetic moment and that successive layers order antiferromagnetically. The exchange asymmetry is predominantly due to spin-flip scattering. The spin-flip spectrum broadens toward lower energy with increasing thickness, suggesting that Cr may have a surface-enhanced magnetic moment
TL;DR: In this article, the spontaneous magnetization of ferromagnetic clusters of various structures and sizes has been modeled with the Heisenberg model, and a self-consistent spinwave-spectrum is found by direct diagonalization of the equation of motion of S+.
TL;DR: It is found that the Haldane phase can be regarded as the special case of the dimer phase of the spin-+ model which also possesses the extended string order and the duality relations between these four phases are proved for several limiting cases.
Abstract: The ground state of the ferromagnetic-antiferromagnetic alternating spin-1/2 Heisenberg chain is studied with Ising-type anisotropy on the ferromagnetic bond. This model tends to the spin-1 antiferromagnetic Heisenberg chain with on-site anisotropy in the limit of strong ferromagnetic bond. It is found that the Haldane-gap phase, the large-D phase, and the two types of N\'eel phases appear as the ground state of this model. The duality relations between these four phases are proved for several limiting cases. The string order parameter characterizing the large-D phase is introduced based on these duality relations. The ground-state phase diagram is determined by the numerical diagonalization of the finite-size system.
TL;DR: The spin-wave spectrum of infinite, semi-infinite, and finite ferromagnetic superlattices with arbitrary elementary units is analyzed theoretically in the exchange-dominated region.
Abstract: The spin-wave spectrum of infinite, semi-infinite, and finite ferromagnetic superlattices with arbitrary elementary units is analyzed theoretically in the exchange-dominated region. The general dispersion equations for spin-wave modes are derived in the framework of the transfer-matrix formalism. Infinite structures with layered defects are also analyzed. Some numerical results are presented for structures with N=1, 2, and 6 atomic planes in the elementary unit. The considerations are restricted to simple cubic structures with the exchange coupling between nearest neighbors.
TL;DR: It is found that substantially better agreement with measured quantities for both structural and electronic properties is achieved with the PW91 approximation than with the LSDA.
Abstract: The electronic structure and total energy of iron are calculated for the fcc and bcc crystal structures using the linear muffin-tin oribtal method in the atomic-sphere approximation (LMTO-ASA). Results obtained using the recently proposed gradient-corrected density functional of Perdew and Wang (PW91) are presented and are compared to those obtained with the local- (spin-) density approximation (LSDA). It is found that substantially better agreement with measured quantities for both structural and electronic properties is achieved with the PW91 approximation than with the LSDA. The effects of including corrections to the ASA are briefly discussed.
TL;DR: Temperature dependence of the rare-earth contribution to magnetocrystalline anisotropy constants and magnetostriction of 3d-4f intermetallic compounds is calculated in an approximation linear in the crystal-field and single-ion magnetoelastic interactions.
Abstract: Temperature dependence of the rare-earth contribution to magnetocrystalline anisotropy constants and magnetorestriction of 3d-4f intermetallic compounds is calculated in an approximation linear in the crystal-field and single-ion magnetoelastic interactions, which are regarded as perturbations with respect to a stronger 3d-4f exchange interaction. The results for an arbitrary quantum number J are compactly formulated in terms of new generalized Brillouin functions which coincide with the known reduced hyperbolic Bessel functions in the classical limit, J\ensuremath{\rightarrow}\ensuremath{\infty}. It is shown, however, that the quasiclassical approximation is inapplicable to the systems concerned. Specific cases of some uniaxial crystal structures are considered, being of interest for permanent magnet applications.
TL;DR: In this paper, the results of broken symmetry ab initio unrestricted Hartree-Fock calculations are used to probe the angular and distance dependence of the magnetic coupling between a pair of iron centers bridged by an oxo ligand.
Abstract: The results of broken symmetry ab initio unrestricted Hartree-Fock calculations are used to probe the angular and distance dependence of the magnetic coupling between a pair of iron centers bridged by an oxo ligand. The specific complex studied was Na 2 [Fe 2 OCl 6 ]. We find the magnetic interaction to be sensitive to the Fe-O distance but rather insensitive to the Fe-O-Fe angle. Further, we calculate J, the Heisenberg coupling constant, to be -170.0 cm -1 , when the Fe-O distance is 1.75 A
TL;DR: In this article, the irreducible tensor method is used to deduce the effective Hamiltonian in the manifold of the ground multiplet of a 3d n ion in a tetrahedral crystal field.
Abstract: We present a theoretical study of the effective exchange interaction arising from the hybridization between the valence-band states and the localized d orbitals of a transition-metal impurity in a II-VI semiconductor. The irreducible tensor method is used to deduce the effective Hamiltonian in the manifold of the ground multiplet of a 3d n ion in a tetrahedral crystal field. There is no coupling in the cases of Sc 2+ and Ti 2+ ions
TL;DR: The magnetic moment of Cr overlayers on Fe(100) was investigated by spin-resolved core level photoemission as mentioned in this paper, and the results suggest that at room temperature the moment of a Cr monolayer on Fe is of the order of 0.5 to 1μB per Cr atom.
Abstract: The magnetic moment of Cr overlayers deposited on Fe(100) was investigated by spin-resolved core level photoemission. Data for the Cr 3p level show that a monolayer of Cr is ferromagnetically ordered with a magnetic moment oriented antiparallel to the Fe moments. The results suggest that at room temperature the moment of a Cr monolayer on Fe is of the order of 0.5 to 1μB per Cr atom.
TL;DR: In this article, the staggered magnetization of the Heisenberg antiferromagnet on triangular lattice is calculated by means of the usual spin-wave theory, and the magnetization is derived from the ground-state energy as its derivative with respect to the staggered field, and given in a form of 1/S expansion, S being the magnitude of spins.
Abstract: The staggered magnetization of the Heisenberg antiferromagnet on triangular lattice is calculated by means of the usual spin-wave theory. The magnetization is derived from the ground-state energy as its derivative with respect to the staggered field, and given in a form of 1/ S expansion, S being the magnitude of spins. The second-lowest correction, a term of O (1/ S ), consists of two contributions; one from the first-order effect of four-boson terms in the Hamiltonian, and another from the second-order perturbation due to a three-boson term. Each contribution diverges when the exchange interaction is isotropic, but the divergent parts of the two contributions are found to cancel, leaving a finite result for the staggered magnetization to this order. Numerical result for the staggered magnetization is S -0.2613+0.0055/ S .
TL;DR: In this paper, the magnetic structure of the magnetization in ferrimagnetic Fe/Gd multilayer films has been investigated and the experimental results of the field and temperature dependence of magnetization agree fairly well with the calculated ones based on the molecular field model.
Abstract: Spin-flop and compensation phenomena of the magnetization in ferrimagnetic Fe/Gd multilayer films have extensively been investigated. It turns out that experimental results of the field and temperature dependence of magnetization agree fairly well with the calculated ones based on the molecular field model. In the calculation, we have obtained the magnetic structure, assuming that the composition is modulated stepwise, and that the exchange interactions in Fe and Gd layers are the same values as those in bulk Fe and Gd metals, respectively. Both longitudinal and transverse magnetoresistances show a crossover near the spin flop field due to the change in the magnetic structure. This crossover behavior is qualitatively well simulated by the calculation on the assumption of the parallel current flow in each atomic layer.
TL;DR: A systematic study of 3s core-level photoemission spectra of Mn and Fe dihalides shows that exchange splitting, intrashell electron correlation, and final-state screening (charge-transfer satellite) effects all contribute to their satellite structures.
Abstract: A systematic study of 3s core-level photoemission spectra of Mn and Fe dihalides shows that exchange splitting, intrashell electron correlation, and final-state screening (charge-transfer satellite) effects all contribute to their satellite structures. In naturally explains both the facts that 3s satellites in ${\mathrm{MnF}}_{2}$ and ${\mathrm{FeF}}_{2}$ can be well understood by the exchange-splitting but that 3s splittings in other compounds are not proportional to their magnetic moments in general. We find that only when the charge-transfer satellite in the 2p spectra is negligible does the 3s splitting reflect the local moment of the ground state.
TL;DR: A widely used self-consistent-field theory in which exchange and correlation is incorporated through the local-density approximation is found to underestimate slightly the magnitude of the interaction, while a nonlocal theory involving a variational solution of the Bethe-Salpeter equation for the density-density correlation function compares well with experiment.
Abstract: We present a detailed comparison between experiment and theory of the magnitude of the exchange-correlation Coulomb interaction in the collective intersubband spin-density excitation of the electron gas confined to GaAs/AlGaAs quantum wells. A widely used self-consistent-field theory in which exchange and correlation is incorporated through the local-density approximation is found to underestimate slightly the magnitude of the interaction, while a nonlocal theory involving a variational solution of the Bethe-Salpeter equation for the density-density correlation function compares well with experiment.
TL;DR: In this paper, a new type of effective field theory (NEFT) was developed for the quantum spin system with anisotropic exchange interaction, and the Curie temperature Tc and spontaneous magnetization m were calculated for all Ising-, Heisenberg- and XY-like spin systems.
Abstract: A new type of effective field theory (NEFT) is developed for the quantum spin system with anisotropic exchange interaction. The calculation is based on a two-atom cluster approximation, and effects from the rest spins are treated by the operator expansion technique assuming Ising character for surrounding spins. The Curie temperature Tc and spontaneous magnetization m are calculated for all Ising-, Heisenberg- and XY-like spin systems, and discussed comparing with results by other traditional pair spin theories. It is practically confirmed that Tc of the NEFT correctly reflects details of the geomtry of the lattice more than coordination number, and that it gives no anti-Curie point even for the XY-like spin system.
TL;DR: In free-standing slabs, the onset of magnetism is obtained for a J value much smaller than in the bulk, i.e., at smaller J values than the ferromagnetic structures.
Abstract: We perform a systematical study of V slabs from one to five planes. Various configurations are considered: ferromagnetic, layered-antiferromagnetic, and in-plane ferromagnetic. The local magnetic moments are deduced, within a Hubbard Hamiltonian, versus the exchange integral J and the lattice parameter. In bulk vanadium, antiferromagnetic structures occur more readily, i.e., at smaller J values than the ferromagnetic structures. In free-standing slabs, the onset of magnetism is obtained for a J value much smaller than in the bulk
TL;DR: In this paper, the high-order corrections in the polarization expansion for the interaction energy of two ground-state hydrogen atoms are computed for a wide range of interatomic distances R. At large R, the convergence radius ρ of the expansion is only slightly greater than unity, e.g. ρ = 1.0000000031 at the van der Waals minimum for the triplet state.
TL;DR: In this paper, the probability of recombination of primary geminate radical pairs derived from optically active methyldeoxybenzoin (MDB) and from diastereomerically pure 2,4-diphenylpentan-3-one (DPP) have been determined in alkyl sulfate micelles of different sizes.
Abstract: The probability of recombination (P r ) of the primary geminate radical pairs derived from optically active methyldeoxybenzoin (MDB) and from diastereomerically pure 2,4-diphenylpentan-3-one (DPP) have been determined in alkyl sulfate micelles of different sizes. These probabilities have been measured by monitoring the extent of isomerization in the recovered ketone as a function of conversion. The P r values for these two ketones, as a function of micelle size, display disparate behavior: P r for MDB increases as the micelle size increases, while P r for DPP decreases as the micelle size increases