Showing papers on "Exchange interaction published in 1971"
TL;DR: In this article, a new approach to the theory of non-ionic chemisorption is proposed which takes account of the strong electron-electron correlation effects on the ad-atom.
93 citations
TL;DR: The magnetic susceptibility of oxidized and reduced spinach ferredoxin has been measured over the temperature range 77–250°K and anomalous behavior is observed in both oxidation states and the data can be interpreted by assuming an exchange interaction between the metal ions.
92 citations
TL;DR: In this paper, the theory of low lying magnetic excitations of KCoF3 is developed and the parameters describing the magnetic interactions are obtained by comparison with the experimental results of the previous paper.
Abstract: For Pt. I see ibid. vol. 4, 2127. The theory of the low lying magnetic excitations of KCoF3 is developed and the parameters describing the magnetic interactions are obtained by comparison with the experimental results of the previous paper. The branch of the elementary excitation spectrum of lowest frequency is well described by a phenomenological model with an effective spin s'=1/2. The exchange interaction has the Heisenberg form, and the pseudo-dipolar form of anisotropic exchange proposed for KCoF3 is shown to be less than 8% of the isotropic exchange. A model which takes the orbital angular momentum of the Co2+ ion into account is developed by relating the elementary excitations to the quasiboson excitations between the ground state and all eleven excited states of the 4T1 orbital level. This model fits the experimental results for the two branches of lowest frequency extremely well. The interaction between real spins is found to of the Heisenberg form and the spin-orbit coupling constant is found to be 82% of the free ion value. Calculations of the relative intensity of neutron scattering as a function of wavevector transfer for the modes belonging to the two lowest branches of magnetic excitations give good agreement with experiment.
90 citations
TL;DR: In this article, the band structure of both paramagnetic and antiferromagnetic γMn is evaluated by G.F.M. with the Slater exchange approximation, and the gap mechanism similar to Cr is found to be effective around N ≈7.3.
Abstract: The band structure of both paramagnetic and antiferromagnetic γMn is evaluated by G.F.M. with the Slater exchange approximation. The observed magnetic moment (2.3µ B ) is self-consistently obtainable, if the full Slater exchange is reduced by about one-half. The situation is the same at Cr. No special charactors are observed in E ( k )-curves of γMn contrary to the case of Cr. Introducing a simple exchange interaction term - J eff δ n 2 by the random phase approximation, we extend Mueller's interpolation scheme to apply to the antiferromegnetic case, and antiferromagnetism in f.c.c. structure is examined within the limit of the rigid band rigid band approximation. If we assume the value J eff =0.060Ry, f.c.c. Mn and f.c.c. Fe are antiferromagnetic and their magnetic moments are determined as 2.3µ B and 0.7µ B , respectively, which are in good agreement with experimental values. In f.c.c. structure the gap mechanism similar to Cr is found to be effective around N ≈7.3. The theoretical prediction seems to b...
86 citations
TL;DR: In this article, the surface and bulk critical exponents of NiO were determined using the molecular field model and qualitative scaling arguments, and it was shown that the surface exchange interaction is weaker than the bulk exchange interaction.
74 citations
TL;DR: In this paper, a band-structure calculation for the ferromagnetic state of iron is given particularly careful treatment, where the roles of intra-atomic exchange and itinerancy in the origin of iron's ferromagnetism are discussed.
Abstract: A new band-structure calculation is reported for the ferromagnetic state of iron, in which the exchange interaction is given particularly careful treatment. A variational procedure was used with the wave functions expanded in terms of tight-binding functions and orthogonalized plane waves. Hybridization and spin polarization of the wave functions were allowed. Correlation corrections were incorporated. The energy bands are somewhat wider than those previously published; comparison is made with photoemission and optical reflection and x-ray emission data. The calculation leads self-consistently to the observed magnetic moment. The roles of intra-atomic exchange and itinerancy in the origin of iron's ferromagnetism are discussed.
67 citations
TL;DR: In this article, the nuclear magnetism is discussed for a system in which each nuclear spin interacts only with electrons on the same atom by the hyperfine interaction, the electrons having the singlet ground state and interacting with an appreciable exchange interaction.
Abstract: Nuclear magnetism is discussed for a system in which each nuclear spin interacts only with electrons on the same atom by the hyperfine interaction, the electrons having the singlet ground state and interacting with an appreciable exchange interaction. As the exchange interaction approaches to the threshold value to induce a spontaneous electron spin ordering, the Curie temperature of the “ nuclear spin ordering ” and the “ nuclear contribution ” to the paramagnetic susceptibility are both raised by the electron exchange enhancement factor and an appreciable electron spin polarization is also induced. There is collective mode of mainly electron spin nature and of mainly nuclear spin nature. The energy gaps at q =0 in their dispersions are obtained in some typical cases.
51 citations
Journal Article•
46 citations
TL;DR: In this article, the Kohn-Sham self-consistent scheme applied to an atomic system was investigated and it was found that while the calculated exchange energies for various atoms were accurate to within 10%, the correlation energies of atoms were too large by 2.
Abstract: In the local-effective-potential approximation of the Kohn-Sham self-consistent scheme applied to an atomic system, it was reported that while the calculated exchange energies for various atoms were accurate to within 10%, the correlation energies of atoms were too large by a factor of 2. A model system is set up to study the reason why the exchange energy estimates are so much better than those of the correlation energy even though they were treated on the same footing. It was found that, in using expressions derived from an infinite electron gas system to study finite systems, the major source of error comes from the fact that the low-lying levels of a finite system are discrete and have finite spacings. The replacement of summation by integration in the perturbation diagrams results in an overestimate of correlation energy, and a small error in the exchange energy in a finite system like an atom.
30 citations
TL;DR: In this article, the angular and temperature dependent ESR line width of single crystals of (CH3NH3)2 MnCl4 and (C2H5NH 3)2 NMCl4 has been narrowed by exchange interaction.
29 citations
TL;DR: In this article, the spin-wave dispersion relations for Gd, Dy, and Ho metal by triple-axis neutron spectrometry were reviewed and the existence of magneto-elastic anisotropy interactions was investigated.
Abstract: Recent measurements of the spin‐wave dispersion relations for Gd, Dy, and Ho metal by triple‐axis neutron spectrometry will be reviewed. Measurements along the c axis have been carried out for each metal at several temperatures, and for Gd additional measurements along the a and b axes have been made at 78°K. Information about the Fourier‐transformed exchange interaction J(q) has been obtained from data analyses, which are based on a simple Hamiltonian containing only exchange interactions for Gd and a Hamiltonian containing exchange interactions plus appropriate anisotropy interactions (the usual frozen lattice model) for Dy and Ho. For both Dy and Ho a satisfactory analysis of the data requires the use of anisotropy interaction parameters which are not in good agreement with the results of macroscopic measurements. The neutron data suggest the existence of other anisotropy interactions, perhaps magnetoelastic, in addition to those usually considered in the frozen lattice Hamiltonian. The dispersion rela...
TL;DR: In this paper, the heat capacity of cobalt formate dihydrate was measured above 1.8 K. The results showed a sharp peak at 5.12 K and the entropy gain above 2 K was estimated to be 0.33 R which is about one half of the total entropy R 1n 2 for S = 1 2.
TL;DR: The total spin state S = 2 belonging to the pair V2+-F--V2 in V-KMgF3 (sA=sB=3/2 for V2+) has been investigated by epr techniques.
Abstract: The total spin state S=2 belonging to the pair V2+-F--V2 in V-KMgF3 (sA=sB=3/2 for V2+) has been investigated by epr techniques. The other total spin states, S=1 and S=3, are not observed because of excessive broadening of the lines. The principal interactions are described by the Hamiltonian JsA, SB+Df(3sAsB7- sA,sB) where the isotropic exchange interaction is J=4.5+or-1.0 cm-1 and the anisotropic interaction is De=-0.0339+or-0.0002cm-1. De is 35% larger than the dipolar interaction calculated on a simple ionic model. Part of this discrepancy is attributed to covalent transfer of the V2+ spin on to the F- ligands which can increase the dipolar interaction by up to about 20% in the present case. The contribution from pseudodipolar exchange is shown to be negligible.
TL;DR: In this article, the authors derived a theoretical expression for the broadening which results from this relaxation process and applied it to the determination of molecular configurations, electron-electron separations and the sign of the exchange interaction.
Abstract: At high temperatures the dominant relaxation process which determines the linewidths in the electron resonance spectra of flexible biradicals is modulation of the scalar electron-electron exchange interaction. In systems of high viscosity, the modulation of the exchange interaction is often quenched, and the rotational modulation of the anisotropic magnetic interactions now constitutes the principal relaxation mechanism. In this paper we derive a theoretical expression for the broadening which results from this relaxation process. The applications of the theory to the determination of molecular configurations, electron-electron separations and the sign of the exchange interaction are illustrated by comparison with the electron resonance spectrum of bis(2,2,6,6-tetramethyl-piperidinol-1-oxyl)carbonate. The theory is also of value in understanding the spectra of partially immobilized biradical spin labels.
TL;DR: In this paper, a new solution procedure for the diffusion problem is presented, with restrictions placed upon the rotational quantum numbers of the molecular ion product, and cross section functions for charge exchange and ion atom interchange processes using the nearest resonance approximation, including allowance for the exchange interaction.
Abstract: Measurements of rate coefficients for the charge exchange collision processes Ar+N2, Ar+CO, Ar+O2, Ar+NO, N+O2, have been made in the energy range 004-2 eV in the injected ion drift tube A new solution procedure for the diffusion problem is presented Data are sensitive to secondary reactions caused by ions produced in the thermalization of the injected ions; systematic studies of suitable buffer gases habe been made to avoid errors arising from these reactions Calculations habe been made of cross section functions for charge exchange and ion atom interchange processes using the 'nearest resonance' approximation, including allowance for the exchange interaction, and with restrictions placed upon the rotational quantum numbers of the molecular ion product
TL;DR: In this article, the high field Zeeman spectra below 20 K on the transition Z1(6H152/) to G1, which displays a pronounced quintet structure, enables an evaluation of the strength of the exchange interaction to be made.
Abstract: Dysprosium phosphate (DyPO4) orders antiferromagnetically at a Neel temperature of 3.4 K; the direction of the sublattice alignment is the c axis of the tetragonal unit cell. This ordered state arises from a combination of dipolar and exchange interaction and is well described by the Ising model for a highly anisotropic system of magnetic ions with ground state g values of gc=19.5 ga=ga' approximately=0. Analysis of the high field Zeeman spectra below 20 K on the transition Z1(6H152/) to G1, which displays a pronounced quintet structure, enables an evaluation of the strength of the exchange interaction to be made. The result is confirmed by a direct determination of the interaction field from high field moment measurements at 0.5 K.
TL;DR: In this paper, the Slater mixed-density approximation is modified so as to retain effects of finite interaction range in the approximate exchange energy, and a correction for finite number of particles makes the proposed exchange-energy approximation exact for 4 He and infinite matter.
TL;DR: In this paper, the crystal structure, electron spin resonance (ESR), and static paramagnetic susceptibility of single crystals of the complex (TCNQ)2-3,3 diethyltiacarbocyanine (DTC) were investigated and the splitting of the ESR spectra was due to the anisotropy of the g-factors of non-equivalent ion-radical chains of TCNQ.
Abstract: An investigation is made of the crystal structure, electron spin resonance (ESR), and static paramagnetic susceptibility of single crystals of the complex (TCNQ)2-3,3 diethyltiacarbocyanine (DTC) It is shown that the splitting of the ESR spectra is due to the anisotropy of the g-factors of non-equivalent ion-radical chains of TCNQ The g-tensor of a single ion-radical chain of TCNQ is found to have molecular symmetry (gxx = 20026, gyy = 20034, gzz = 20021; all ±00003) The existence of splitting of the ESR spectra gives evidence that there is no exchange interaction between non-equivalent chains However, the measurements of the static paramagnetic susceptibility and the linewidth analysis indicate that the intra-chain exchange interaction I/K has a large value: 10 to 15° Thus, our results show that the spin system in the complex (TCNQ),-DTC is one-dimensional
[Russian Text Ignore]
TL;DR: In this article, an explanation for the ferromagnetism of semiconducting EuB 6 as contrasted with the antiferromagnetic properties of metallic GdB 6 is suggested, based on the Bloembergeb-Rowland exchange interaction.
TL;DR: A generalization of expressions for the anisotropic exchange interaction for the case of nonequal spins of separate ions for the ground and excited states was developed in this article, where the generalization was extended to the special case of ion spin configurations.
Abstract: A generalization of expressions for the anisotropic exchange interaction is developed for the case of nonequal spins of separate ions for the ground and excited states.
TL;DR: In this paper, the exchange interaction between pairs of V2+ ions occupying substitutional cation sites in magnesium oxide has been studied by electron paramagnetic resonance and the interaction is found to be ferromagnetic with J=-7.5+or-3 cm-1.
Abstract: The exchange interaction between pairs of V2+ ions occupying substitutional cation sites in magnesium oxide has been studied by electron paramagnetic resonance. For next nearest neighbour pairs coupled via an intervening oxygen ion, transitions within the total spin state S=2 only are observed. Transitions within the S=1 and S=3 levels are broadened by interactions which leave the S=2 level unaffected. The exchange-induced fine structure splitting, De, is almost a factor of two larger than the dipolar term Dd. Although lattice distortion, covalent spin transfer to the ligands and anisotropic exchange interactions may contribute to this discrepancy a significant part must come from so far undetermined mechanisms. The nearest neighbour pairs, which are at right angles with respect to an intervening anion, have been studied in less detail. The interaction is found to be ferromagnetic with J=-7.5+or-3 cm-1.
TL;DR: In this paper, Abrikosov et al. used the parquet theory to derive the sum of the most divergent sub-series of the perturbation expansion of the Fermi surface.
Abstract: •1 ) explained the phenomenon on the resistance minimum in dilute magnetic alloys, a new electron state appearing below some characteristic tem perature, say T x, has attracted a great interest This new electron state seems to be associated with the occurrence of the resonance scattering of conduction electrons by magnetic impurities and this resonance nature makes the treatment of the problem very difficult Kondo 1 ) has assumed the exchange interaction between conduction electrons and an impurity spin, the so-called s-d exchange interaction As pointed out by him, the non-commutativity of the spin operator and the sharpness of the Fermi surface have brought about a characteristic feature to s-d problem, namely the logarithmic divergence at the Fermi surface In more detail, the perturbation expansion turns to contain a term such as Jn (ln D / E)m, in which J is the exchange coupling constant Abrikosov 2 ) succeeded for the first time in summing up the most divergent sub-series of the perturbation expansion, using the so-called parquet theory As is the case with an electron gas, if the coupling is ferromagnetic, the sum thus obtained is finite over the whole range of energy Moreover, the sum of the next divergent sub-series turns out to be also finite and of order J as compared with the former and so on Here we notice that the sums of the next and the lower divergent terms can· be calculated from some skeleton diagrams in a simple manner; replacing the basic vertex J by the parquet diagram r and inserting the self-energy correction which itself is the sum of the most divergent corrections In this way, one may finally obtain the rearranged series of the perturbation ex
TL;DR: In this paper, the reflectivity spectra of the Z1,2 and Z3 exciton bands in CuCl were analyzed under uniaxial stress by Koda and co-workers.
TL;DR: The method of effective Hamiltonian (EFH) was applied to the excited state (2E4A2) fine structure of Cr3+−Cr3+ fourth order pairs in ruby.
Abstract: The method of effective Hamiltonian (EFH) is applied to the excited state (2E4A2) fine structure of Cr3+–Cr3+ fourth order pairs in ruby. Comparison with experimental data illustrates the importance of both the anisotropic and antisymmetric exchange interactions, and that part of isotropic exchange interaction, which is nondiagonal in the orbital variables. Various microscopical mechanisms responsible for terms in the effective Hamiltonian are discussed.
[Russian Text Ignored].
TL;DR: In this article, a coherent state representation for the spin system was defined by transforming the Heisenberg model Hamiltonian to Bose operators, which proved to be a useful basis for evaluating the partition function in a manner similar to that used previously for a superfluid.
TL;DR: In this paper, the nonlocal pseudopotentials in the OPW formalism are determined for sodium and potassium from the experimental data in the radial distortion of the Fermi surfaces, by taking the core shift in the pseudopotential as an only adjustable parameter to fit the data.
Abstract: The nonlocal pseudopotentials in the OPW formalism are determined for sodium and potassium from the experimental data in the radial distortion of the Fermi surfaces, by taking the core shift in the pseudopotential as an only adjustable parameter to fit the data. It is found that the exchange interaction between core and conduction electrons should be treated properly without using the approximate form like the slater exchange to find a reasonable value for the core shift parameter. The exchange and correlation effects among conduction electrons are taken into account in the approximate form proposed recently by Kleinman and are found to be also important. The nonlocality of the determined pseudopotentials is quite significant; the validity of the local pseudopotential approximation seems rather limited. The reason why the analysis of the Fermi surface distortion by using the local pseudopotential has been quite successful for Na but not for K is discussed.