Showing papers on "Exchange interaction published in 1973"
IBM1
TL;DR: In this article, the exchange energy is found for electrons in a two-dimensional system and in Si inversion layers which are dynamically two dimensional, and it is shown that exchange lowers the energy of the lowest subband significantly, but affects the energies of higher sub-bands and the spatial extent of the wave functions in the direction perpendicular to the surface only slightly.
Abstract: The exchange energy is found for electrons in a two-dimensional system and in Si inversion layers which are dynamically two dimensional. We find that exchange lowers the energy of the lowest sub-band in Si inversion layers significantly, but affects the energies of higher sub-bands and the spatial extent of the wave functions in the direction perpendicular to the surface only slightly.
85 citations
TL;DR: In this paper, the stochastic Liouville method has been applied to the problem of high field CIDEP and CIDNP, and the solution of the problem approach those obtained by Adrian using the Noyes molecular pair theory.
Abstract: The stochastic Liouville method has been applied to the problem of high field CIDEP and CIDNP. The full equation of motion of the density matrix for the pair of free radicals includes: (1) the spatially isotropic Liouville operator; (2) the diffusion operator; (3) selective recombination of radical pairs from the singlet electronic state; (4) the Heisenberg exchange interaction; (5) secular electronic relaxation processes; and (6) radical scavenging processes. The short range character of radical recombination and Heisenberg exchange relative to the long distance of a diffusive trajectory allows these interactions to be treated effectively as delta functions which operate at a distance corresponding to a chemical bond. Using this delta function model, the equation of motion of the density matrix is soluble exactly for: (1) the z component of the electronic magnetization for a single radical fragment, which is proportional to the intensity of an ESR line; and (2) the nuclear spin level populations of the recombination and scavenged products, which are the indirect observables in the NMR experiment. In the limits of weak electronic relaxation and slow scavenging, the solutions of the problem approach those obtained by Adrian using the Noyes molecular pair theory.
79 citations
TL;DR: In this paper, the discrepancy between the Gd EPR g shift and linewidth in YCu, YAg, and LaAg is resolved using a wave vector dependent exchange parameter J(k,k').
71 citations
TL;DR: In this paper, the optical absorption spectra of HgCr 2 Se 4 single crystals in the intrinsic transition region were measured as a function of magnetic field at a number of fixed temperatures.
Abstract: The optical absorption spectra of HgCr 2 Se 4 single crystals in the intrinsic transition region were measured as a function of magnetic field at a number of fixed temperatures. The absorption edge, 0.80 eV, at room temperature shifted to 0.27 eV at liquid helium temperature. The temperature dependence of the absorption edge was nonlinear and remarkable around the Curie temperature. The absorption edge also shifts to the lower energy side with the increasing magnetic field. The field dependence of the edge shift in weaker magnetic field was larger at the Curie temperature than it in the higher temperature region. The temperature and magnetic field dependence of the absorption edge was compared to a calculated spin correlation function in spinels with the nearest neighbour exchange interaction between localized Cr +3 ions. Other kind of exchange interaction would be required to explain the temperature dependence of the absorption edge.
53 citations
TL;DR: In this paper, the perturbation expansion in the electron-electron interaction is used to calculate the correction to the local-density approximation of the exchange energy in atoms, which gives better results than the random-phase approximation.
Abstract: Recent theories of Singwi et al. for the dielectric response beyond the random-phase approximation are examined in the density-functional formalism. Their approximation and another from the perturbation expansion in the electron-electron interaction are used to calculate the correction to the local-density approximation of the exchange energy in atoms. The latter gives better results.
46 citations
TL;DR: The theory of the magnetic excitations at low temperatures has been developed with the aid of the pseudo-boson technique in terms of the crystal field and spin-orbit parameters of the individual ions and of the exchange interactions between neighbouring ions.
Abstract: The magnetic excitations of cobalt fluoride have been studied both theoretically and experimentally. The theory of the magnetic excitations at low temperatures has been developed with the aid of the pseudo-boson technique in terms of the crystal field and spin-orbit parameters of the individual ions and of the exchange interactions between neighbouring ions. The model with surprisingly simple forms of exchange interaction gives a very good description of many of the experimental results. Measurements of the longitudinal spin correlations near the Neel temperature have been made with slow neutron inelastic scattering techniques. The results show that the longitudinal spin correlations have a small frequency width; the width at half maximum of the quasi-elastic peak is, at all temperatures and wavevectors, less than 0.12 THz.
41 citations
TL;DR: In this paper, the Ruderman-Kittel-Kasuya-Yosida interaction between localized magnetic spins on the basis of perfectly free conduction electron is calculated as a function of the Fermi wave vector of the conduction electrons.
35 citations
TL;DR: In this article, an analysis of the effects of small polaron formation on the metal insulator transition as expressed in terms of the Hubbard model is presented, where the electron-excitation coupling is treated by a canonical transformation that leads to reduced Hubbard constants for both the Coulomb interaction and the bandwidth.
Abstract: An analysis of the effects of small polaron formation on the metal‐insulator transition as expressed in terms of the Hubbard model is presented. The system dealt with contains an electronic subsystem and a rigid lattice of polarizable molecules. The electron‐excitation coupling is treated by a canonical transformation that leads to reduced Hubbard constants for both the Coulomb interaction and the bandwidth. Polaron formation leads in addition to the creation of a polarization bond in the crystal. This contribution to the total cohesive energy of the solid is shown to be equal in magnitude to the polaron binding energy. The effective antiferromagnetic exchange interaction (via virtual charge transfer) is calculated for both excitonic and phononic polarons. A discussion of the effect of increased polarizability is presented with emphasis on the possibility of stabilizing the metallic phase at low temperatures in real crystals.
34 citations
TL;DR: In this article, the authors examined the properties of a model which exhibits this behavior from a theoretical point of view and showed that the model can explain some aspects of recent observations of spin polarized photoemission from the surface of EuO.
33 citations
TL;DR: In this article, the second-order exchange energy predicted by the Murrell-Shaw and Musher-Amos (MS-MA) theory was evaluated analytically for the hydrogen molecule ion.
Abstract: The exchange polarization energy and higher-order exchange corrections arising in the second order of the Murrell-Shaw and Musher-Amos (MS-MA) theory are evaluated analytically for the hydrogen molecule ion. At large internuclear distances the second-order exchange energy predicted by MS-MA theory behaves like . It represents only 80% of the difference between the exact result of Holstein and the asymptotic value of the first-order exchange energy. The same result holds for the case of Hirschfelder-van der Avoird (HAV) and Hirschfelder-Silbey (HS) theories.
32 citations
TL;DR: In this paper, specific-heat and magnetothermal experiments are described that prove the existence of a phase transition of these effective spins when the effective field differs not too much from zero, and the results of this investigation are collected in the conclusion at the end of the paper.
TL;DR: In this paper, Landau's theory of Fermi liquid is applied to obtain the quasi-particle parameters of the interacting two-dimensional electrons in the surface inversion layers of silicon.
Abstract: Landau's theory of Fermi liquid is applied to obtain the quasi-particle parameters of the interacting two-dimensional electrons in the surface inversion layers of silicon. The calculated g -factor exhibits a good agreement with the experimental results of Fang and Stiles over a wide range of electron concentration and supports on a firmer ground Janak's original suggestion that the deviation of the g -factor from the bulk value is caused by the exchange interaction among surface electrons. Similar effects on the effective mass are briefly discussed.
TL;DR: In this article, the metal-to-insulator transition in V2O3 is described by a model that is based on the electronic band structure of this material, and various aspects of the transition, such as changes in the c/a ratio, the creation of magnetic moments, changes in covalency, the effect of p...
Abstract: The metal-to-insulator transition in V2O3 is described by a model that is based on the electronic band structure of this material. The vanadium 3d-t 2g band decomposes in the trigonal symmetry into two bands, a 1g and e π. The a 1g band consists of orbitals connecting pairs of c-axis neighbouring atoms, while the e π band consists of orbitals in the plane perpendicular to the c-axis. The change in distance between c-axis neighbours changes the nature of the a 1g band from molecular (delocalized) to atomic (localized). The localization of the a 1g electrons causes through the atomic exchange interaction also the localization of the e π electrons, and this localization creates a gap in the e π band which causes the material to become insulating. This model is treated in the Hartree-Fock approximation (the ‘Excitonic’ model) at zero and finite temperatures, and various aspects of the transition, such as changes in the c/a ratio, the creation of magnetic moments, changes in covalency, the effect of p...
TL;DR: In this article, the magnetic susceptibilities of the compounds AFeCl3(A=Tl,Rb,NH4,Cs) were investigated in the temperature region 2 −250°K.
Abstract: The magnetic susceptibilities of the compounds AFeCl3(A=Tl,Rb,NH4,Cs) were investigated in the temperature region 2–250°K. The results are interpreted in terms of an antiferromagnetic linear‐chain model. The values of the effective anisotropic intrachain exchange interaction are calculated. The exchange interaction depends on the distance between neighboring Fe2+ ions in the chains.
TL;DR: In this paper, the problems on the magnetic dilution in the ferromagnetic system are discussed by the use of the Ising model of spin 1/2, where the exchange interaction between nearest neighbors, the next nearest neighbor (n.n.) interaction has been taken into consideration, and the magnetic properties are calculated by the method of concentration expansion.
Abstract: The problems on the magnetic dilution in the ferromagnetic system are discussed by the use of the Ising model of spin 1/2. In addition to the exchange interaction between nearest neighbors, the next nearest neighbor (n.n.n.) interaction has been taken into consideration, and the magnetic properties are calculated by the method of concentration expansion. Particularly the critical concentration and the concentration dependence of the Curie temperature have been calculated for several lattice structures. In some crystal lattices, the n.n.n. interaction concerns to the change of the dimensionality of the magnetic lattice and then the effects of the n.n.n. interaction are quite remarkable in the concentration dependence. The numerical values of the critical concentration and the Curie temperature calculated in the present method are compared with the results previously calculated by various methods and good agreement is obtained.
TL;DR: The general solution of the Luttinger-Tisza approximation for the ground state of crystals with dipole-dipole and exchange interaction is given for crystals with two equivalent magnetic ions (or atoms) per unit cell in this article.
TL;DR: In this paper, the band structure of crystalline methane has been calculated in a linear-combination-of-molecular-orbitals approximation, where the Bloch sums are built up of Hartree-Fock orbitals of free molecules.
Abstract: The band structure of crystalline methane has been calculated in a linear-combination-of-molecular-orbitals approximation. In this molecular tight-binding method the Bloch sums are built up of Hartree-Fock orbitals of the free molecules. Interactions between the states of different molecules are calculated directly from molecular integrals without reducing the exchange interaction to an exchange potential. The approximations involved are shown to be well justified for a crystal made of closed-shell units. The band structure is obtained by solving secular equation in 400 points along the relevant symmetry lines. The calculated bands are relatively narrow, less than 2.5 eV wide, around the molecular levels. The band-to-band gap in solid methane is 24.5 eV. This value has the same order of magnitude as in solid rare gases.
TL;DR: In this article, an explicit expression for the exchange interaction between two weakly coupled atoms A and B in the state of highest multiplicity was obtained using the symmetric double coset (SDC) expansion of permutation groups.
TL;DR: In this article, the magnetic critical scattering from a single crystal of γ-Fe 0.537 Mn 0.463 has been studied around the (001) and (110) reciprocal lattice points.
Abstract: The magnetic critical scattering from a single crystal of γ-Fe 0.537 Mn 0.463 has been studied around the (001) and (110) reciprocal lattice points. It has been found that the longitudinal spin correlation becomes divergent at the Neel temperature T N of 479.0±1.5 K, the parallel staggered susceptibility χ // ( Q ) obeys a power law of α( T - T N ) -1.35±0.05 , in contrast with the temperature independent static susceptibility. The transverse spin correlation, however, remains finite at T N with the inverse correlation length of about 0.038 A -1 . The anisotropy of the spin correlation has been suggested not due to the crystal anisotropy, but to either the anisotropic exchange interaction or the anisotropy of the non-interacting spin susceptibility of d bands. The anisotropy of the scattering profile with respect to the wave vector around the reciprocal lattice points has been found much smaller than that expected for the type I antiferromagnet with the short range interactions.
TL;DR: In this paper, it was shown that at sufficiently large R a given induced 2l-pole exchange energy can be computed with a high accuracy using a simplified form of the polarization function obtained with neglect of charge overlap effects.
Abstract: The exchange polarization energy for the H2+ ion is expressed as an infinite sum of its angular components. At large internuclear distances R, a particular l-component, referred to as induced2l-pole exchange energy, behaves asymptotically like
For larger R this suggests a rather slow l−4 rate of convergence of the series. However, as contrasted to the analogous expansion for the induction energy the convergence speeds up considerably with decreasing internuclear separation.
It is also shown that at sufficiently large R a given induced 2l-pole exchange energy can be computed with a high accuracy using a polarization function obtained with neglect of charge overlap effects. Near the bottom of the van der Waals minimum over 99% of the exchange polarization energy can be produced using this simplified form of the polarization function.
TL;DR: In this article, the asymptotic calculation of the exchange interaction between two atoms with the same ionization potentials is carried out and it is established that the second term (of relative order R−1/2) of the series becomes zero.
Abstract: The asymptotic calculation of the exchange interaction between two atoms with the same ionization potentials is carried out. It is established that the second term (of relative order R
−1/2) of the asymptotic series becomes zero. The dependence of the atom-molecule exchange interaction on vibrational coordinates is also discussed.
TL;DR: In this article, the relationship between the multiplet splitting in core electron binding energies of radicals and the unpaired orbital spin density distribution is developed and an explicit formula derived, and the atomic intershell exchange interaction is shown to be important to determining magnitudes and trends in the multi-particle splitting.
TL;DR: The Nd monopnictides NdP, NdAs and NdSb are simple cubic type I antiferromagnets in which the crystal-field splitting is larger than the exchange energy.
Abstract: The Nd monopnictides NdP, NdAs and NdSb are simple cubic type I antiferromagnets in which the crystal-field splitting is larger than the exchange energy. The magnetic properties are calculated by means of a mean-field theory including crystal-field and magnetoelastic effects. The calculations are based on energy levels determined by inelastic neutron diffraction. Exchange constants are derived by comparing the theoretical paramagnetic susceptibility with experiments over a large temperature range. The temperature dependence of the sublattice magnetization deviates significantly from the usual molecular field curve (for J=9/2) which neglects crystal-field effects. Theoretical high-field magnetization curves are presented. The observed tetragonal distortion below the Neel temperature TN is explained by the theory. The effect of biquadratic exchange interaction is investigated.
TL;DR: In this paper, it was shown that in systems with single-electronic ground states the simultaneous diagonalization of a hyperfine, as well as an exchange interaction, gives rise to an interference between these two effects which has important consequences on the properties of such a system.
Abstract: It is shown that in systems with single-electronic ground states the simultaneous diagonalization of a hyperfine, as well as an exchange interaction, gives rise to an interference between these two effects which has important consequences on the properties of such a system. It is found, for example, that long-range order is now possible for values of the exchange below that previously thought necessary. Calculations are presented for the magnetic moment, heat capacity, susceptibility, and collective modes for a system involving praseodymium.
TL;DR: In this article, the problem of direct exchange between two Tg ions coupled to the Eg types of distortions of a cubic lattice was studied, and it was found that the exchange interaction has a complicated form, that in general it is quenched, and that it may become temperature dependent.
Abstract: The Jahn-Teller coupling is known to lead to the reduction of single parameters such as the spin-orbit coupling (the Ham effect). An important question is what it does to exchange interactions. This problem is studied for what is probably the simplest case, direct exchange between two Tg ions coupled to the Eg types of distortions of a cubic lattice. It is found that the exchange interaction has a complicated form, that in general it is quenched, and that it may become temperature dependent. The method used is a combination of the transformation method for Jahn-Teller problems and a new formulation of the exchange problem, in terms of second quantization.
TL;DR: In this paper, the spin Hamiltonian parameters for the coupled species (S=1) are:g = 2.1025,g += 2.031,A=75.1×10−4 cm−1,B=14.8×10 −4,D=276.0×10 ¼ 4 cm− 1 andE=46.7×
Abstract: ESR investigations on exchange coupled pairs of Cu ions in single crystals of Cu(dtc)2, isomorphously diluted with the corresponding diamagnetic zinc salt, are reported. The spin Hamiltonian parameters for the coupled species (S=1) are:g
‖=2.1025,g
+=2.031,A=75.1×10−4 cm−1,B=14.8×10−4,D=276.0×10−4 cm−1 andE=46.7×10−4 cm−1. While theg andA tensors show tetragonal symmetry, the zeor-field splitting tensor is rhombic and has principal axes different from those of theg andA tensors. Intensity measurements made down to 4.2 K indicate that the exchange is ferromagnetic with |FFF| ∼ 10 cm−1. Direct dipole-dipole interaction appears to be the major contribution to the zero-field splitting. A calculation on the distributed point dipole model shows that dipolar interaction is considerably modified by the high covalency of the Cu-S bond and accounts for the rhombic nature of the tensor. The possible exchange mechanisms in Cu(dtc)2—direct exchange and superexchange through the bridging sulphurs—are discussed.
TL;DR: In this paper, it was shown that in exchange-enhanced alloys the $d$-hole intra-atomic exchange energy is modified at host sites with magnetic impurities as near neighbors.
Abstract: In this paper it is postulated that in exchange-enhanced alloys the $d$-hole intra-atomic exchange energy is modified at host sites with magnetic impurities as near neighbors. When this effect is statistically averaged over the alloy, the exchange enhancement that results is concentration dependent. When applied to PdFe, it is shown that one can thereby account for the rapid increase in the concentration dependence of nuclear spin-lattice relaxation rates for both Fe and Pd sites from about 3-at.% Fe on down and for the sharp peak in the concentration dependence observed at about 0.5-at.% Fe. The model is also applied to a computation of the acoustic spin-wave stiffness constant $D$. The resulting curve for $D$ vs iron concentration $c$ bends over sharply at $c$ between 1 and 3-at.% Fe, in agreement with the observed concentration dependence of $D$ in PdFe.
TL;DR: A suitable representation for the electron atom interaction is also discussed in this article, where different cases of exchange interaction in the system (A+e+C+) are considered and corresponding expressions for this interaction are obtained.
Abstract: Different cases of the exchange interaction in the system (A+e+C+) are considered and corresponding expressions for this interaction are obtained. A suitable representation for the electron atom interaction is also discussed.