Showing papers on "Exchange interaction published in 1976"
TL;DR: In this article, a model for exchange interaction taking into account the impact of the m.o.s. concept in inorganic chemistry was proposed, which is applied to the study of binuclear complexes of chromium(III).
Abstract: A model is proposed for exchange interaction taking into account the impact of the m.o. concept in inorganic chemistry. We define four principles that such a model should follow; invariance with respect to a unitary transformation between the orbital basis functions, validity of Heitler–London wavefunctions for the low lying terms, no difference in nature between direct and indirect exchange interactions, and the possible interpretation of the phenomenon by considering only the ground configuration (the coupling between ground and charge transfer configurations only leads to a small second order effect). Within this framework, we express the interaction hamiltonian as the sum of a one-electron operator coupling the magnetic orbitals in such a way that its eigenfunctions and eigenvalues are respectively the m.o.s. built from the magnetic orbitals and their energies, and a bielectronic operator. When the magnetic orbitals of similar symmetry are not orthogonal, the effect of the one electron operator on the energy differences between the low lying terms is largely predominant. The model is applied to the study of binuclear complexes of chromium(III).
228 citations
TL;DR: In this article, a general group-theoretical scheme is developed to discuss any symmetry-breaking effects on the 12fold $1s$-exciton states originating from an $s$like and $p$-like electron-hole pair.
Abstract: A general group-theoretical scheme is developed to discuss any symmetry-breaking effects on the 12-fold $1s$-exciton states originating from an $s$-like and $p$-like electron-hole pair. All the possible effects on the conduction and valence bands are taken into account by an effective Hamiltonian formalism. For the electronhole exchange interaction, the simplest term (including dipole-dipole interaction) is considered. The symmetry-breaking effects treated here can be anything; e.g., a magnetic field, an electric field, stress, the finiteness of exciton wave vector, etc., and even the products of them. As a group-theoretical treatment, this theory includes all the relevant previous theories as special cases.
155 citations
TL;DR: In this article, a prescription for exchange and correlation in the density-functional formalism with a nonlocal density dependence is given, which is exact in the almost homogeneous limit, charge-conserving, and always finite.
116 citations
TL;DR: In this article, the spin-orbit coupling constant, ξ2p, has been shown to be essentially invariant over the oxidation state range 0 to VI, and it has thus been possible to describe the alterations in the 2p separations in terms of covalency effects which modify the degree of exchange interaction.
111 citations
IBM1
TL;DR: In this paper, the Mossbauer spectrum was analyzed in terms of a distribution of hyperfine fields which suggests a spatial distribution of magnetization that is compatible with the exchange fluctuation as deduced from the temperature dependence of magnetisation.
Abstract: Experimental results of magnetization and M\"ossbauer measurements on an amorphous alloy ${\mathrm{Fe}}_{75}$${\mathrm{P}}_{15}$${\mathrm{C}}_{10}$ are presented to show that there is a sizable fluctuation in exchange interaction in amorphous ferromagnets. Like several other amorphous ferromagnetic alloys, the spontaneous magnetization as a function of the reduced temperature for the amorphous alloy falls characteristically below those of crystalline ferromagnets such as ${\mathrm{Fe}}_{3}$P and Fe. A comparison of the magnetization data with Hadrich's theory for amorphous ferromagnets suggests that in the amorphous alloy the average variation in the exchange constant ($J$) can be as large as $J$ itself. The M\"ossbauer spectrum is analyzed in terms of a distribution of hyperfine fields which suggests a spatial distribution of magnetization that is compatible with the exchange fluctuation as deduced from the temperature dependence of magnetization. The origin of magnetization fluctuation in amorphous alloys is discussed. It is pointed out that a broad distribution of magnetic ordering is consistent with the experimental observation of the coexistence of Kondo-type resistance minimum and ferromagnetism in amorphous alloys.
93 citations
TL;DR: In this article, a previously described model for exchange interaction is applied to the study of antiferromagnetic coupling in binuclear oxo-bridged iron (III) complexes.
Abstract: A previously described model for exchange interaction is applied to the study of antiferromagnetic coupling in binuclear oxo-bridged iron (III) complexes The energies of the magnetic orbitals (singly occupied d orbitals of each transition ion, partially delocalized towards the ligands surrounding this ion), and of the mos built from these magnetic orbitals are calculated, using the Angular Overlap Model The wavefunctions associated with the low lying terms are expressed in the form of HL functions and the relative energies of these terms are calculated from a one electron matrix, which couples the magnetic orbitals in such a way that its eigenfunctions an eigenvalues are the mos and their energies An interpretation of the relative magnitudes of antiferromagnetic coupling in FeIII—O—FeIII and CrIII—O—CrIII dimers is proposed
81 citations
TL;DR: A two-iron-two-sulphur non-haem iron protein, the ferredoxin from Spirulina maxima, has been studied by means of electron paramagnetic resonance (EPR) in the range where the spectrum loses resolution with increasing temperature.
55 citations
TL;DR: In this article, an exactly soluble model for a spin-glass phase transition is presented, which is essentially a mean-field theory; but instead of "bond" randomness of the exchange interaction (as used by other authors), a site randomness is assumed.
Abstract: An exactly soluble model for a spin-glass phase transition is presented. It is essentially a mean-field theory; but instead of "bond" randomness of the exchange interaction (as used by other authors), a "site" randomness is assumed. This enables one to calculate the "quenched" free energy without any uncertain mathematical procedures. Typical results are given for a variety of interesting cases.
52 citations
01 Sep 1976
TL;DR: In this article, the present state of knowledge and understanding of the basic magnetic properties of amorphous alloys is reviewed, including magnetic moments, exchange interaction, temperature dependence of the magnetization and anisotropy.
Abstract: The present state of knowledge and understanding of the basic magnetic properties of amorphous alloys is reviewed. It covers magnetic moments, exchange interaction, temperature dependence of the magnetization and anisotropy for two categories: metal‐metalloid and rare earth‐transition metal amorphous alloys. Some apparent discrepancies in our present knowledge are pointed out.
45 citations
TL;DR: A review of theoretical concepts and experimental data concerning the spin-Peierls transition in a one-dimensional spin system with antiferromagnetic exchange interaction is given in this article.
Abstract: A review is given of theoretical concepts and experimental data concerning the spin-Peierls transition in a one-dimensional spin system with antiferromagnetic exchange interaction (an analog of Peierls instability of a one-dimensional metal). Analysis of experimental data confirms the existence of the spin-Peierls transition in TTF-CuBDT, TTF-AuBDT, and MEM(TCNQ)2 crystals. The magnitude of the spin-phonon interaction in crystals undergoing the spin-Peierls transition at low temperatures is discussed together with the role of fluctuations in transitions of this type. The influence of magnetic fields on spin-Peierls transitions is examined.
45 citations
TL;DR: The magnetic phase diagram and properties of TbCu 1-X Zn X system with the cubic CsCl type structure have been studied by neutron diffraction and magnetic measurements as mentioned in this paper.
Abstract: Magnetic structure of TbCu 1- X Zn X system with the cubic CsCl type structure has been studied by neutron diffraction and magnetic measurements. In Cu-rich region ( X <0.5). the antiferromagnetic structure is conserved, which is TbCu type with (π π 0) mode. When X increases further, the magnetic state suddenly transforms to a ferromagnetic state with canted spin arrangement of which antiferromagnetic mode is (π π 0). In the region with the canted spin arrangement (0.5< X <0.7), the magnetic state approaches to a simple ferromagnetic state with increasing temperature, and transforms not only to a complete ferromagnetic state with increasing temperature, and transforms not only to a complete ferromagnetic state, but also directly to a paramagneticstate. This magnetic phase diagram and properties are fairly well explained by the theory based on the s-f exchange interaction with the low density 4s-electrons, assuming the electronic band structure of YZn.
TL;DR: In this article, a time-dependent radial density function is proposed to describe the distribution of acceptor molecules around donors, and an analytic equation is derived for the increase in the effective encounter distance as the diffusion coefficient decreases.
Abstract: Static quenching by dipole–dipole and exchange mechanisms is discussed in terms of a time dependent radial density function, which describes the distribution of acceptor molecules around donors. The final equations for the time dependence of the donor concentration agree with those derived previously using an alternative technique. The radial density function provides a helpful physical insight into the short comings of the active sphere treatment. The effect of an exchange interaction on diffusion-controlled reactions is discussed, and an analytic equation derived for the increase in the effective encounter distance as the diffusion coefficient decreases. The transition from diffusive to static quenching is discussed, and the two regions linked qualitatively.
TL;DR: In this paper, the spin wave interaction plays a rather important role in the nearly two-dimensional magnetic system and gives rise to a logarithmic term in the expansion of the magnetization with respect to the temperature.
Abstract: The temperature and the magnetic field dependences of the magnetization of the ferromagnetic layer-type compound K 2 CuF 4 have been analyzed by the spin wave theory which takes into account the spin wave interaction. It is shown that the spin wave interaction plays rather important role in the nearly two-dimensional magnetic system and gives rise to a logarithmic term in the expansion of the magnetization with respect to the temperature. The apparent T 3/2 temperature dependence of the magnetization can be shown to be realized in a certain temperature region. With the use of the exchange interaction constants estimated in the previous investigations, the present calculation shows excellent agreements with the experiments.
TL;DR: In this paper, the effect of exchange interaction between electrons on the electron-phonon interaction in metals was studied within the generalized random phase approximation, and the phonon frequency of a metal was found to be closely related to the magnetic susceptibility of the metal.
Abstract: The effect of the exchange interaction between electrons on the electron-phonon interaction in metals is studied within the generalized random phase approximation. The phonon frequency of a metal is found to be closely related to the magnetic susceptibility of the metal. The sound velocity of the jellium model, for instance, is inversely proportional to the square root of the paramagnetic spin susceptibility. In particular, in the jellium model the occurrence of a charge density wave and a spin density wave is found to be simultaneous. Finally, the electron-phonon coupling constant λ is found to be enhanced significantly by the exchange interaction.
TL;DR: In this article, a canting spin ordering mechanism for degenerate antiferromagnetic semiconductors based on the s - f exchange model is studied. But the phase diagram is different from that in the double exchange model, and the canting ordering can exist only for a finite value of concentration with a nearly constant ferromagnetic component in the whole temperature range.
Abstract: A canting spin ordering mechanism in degenerate antiferromagnetic semiconductors is studied based on the s - f exchange model. It is shown that even in the broad band case, as is similar to the double exchange mechanism for the narrow band case, the canting spin ordering is stable in low concentration of the conduction electron where the Fermi energy is comparable to or smaller than the s - f exchange energy. The phase diagram is different from that in the double exchange, the canting ordering can exist only for a finite value of concentration with a nearly constant ferromagnetic component in the whole temperature range and thus makes the transition to the ferromagnetic ordering with increasing temperature. These properties are consistent with the experiments in La 1- x Ca x MnO 3 and TbCu 1- x Zn x .
TL;DR: In this article, the Hamiltonian for a completely degenerate d-band including intra-atomic Coulomb and exchange interactions is derived and studied using the alloy analogy method, and the dependence of the magnetization on the exchange constant and on the number of electrons per atom is calculated for strong Coulomb correlation and for uncorrelated case.
Abstract: The Hamiltonian for a completely degenerate d-band including intra-atomic Coulomb and exchange interactions is derived and studied using the alloy analogy method. Green's function, the magnetic susceptibility and a criterion for the appearance of ferromagnetism are obtained by this method. The dependence of the magnetization on the exchange constant and on the number of electrons per atom is calculated for strong Coulomb correlation and for the uncorrelated case. It is shown that Coulomb correlation of any strength leads to a decrease of the exchange interaction constant needed to produce ferromagnetism and additionally to a change in the shapes of the magnetic dependences for (and only for) weakly ferromagnetic metals.
[Russian Text Ignored.]
TL;DR: In this article, the nuclear magnetic resonances of Y2(FexCo1-x)17 and Y(FeyCo 1-y)5 were observed at liquid N 2 temperature using the spin echo method.
Abstract: Nuclear magnetic resonances of Y2(FexCo1-x)17 and Y(FeyCo1-y)5 are observed at liquid N2 temperature using the spin echo method. A different Y2(FexCo1-x)17 NMR behavior from that of Y(FeyCo1-y)5 is interpreted by the existence of antiferromagnetic exchange interaction of the Fe–Fe pair, with the shortest distance in Y2(FexCo1-x)17. Intensity changes with x of Y2(FexCo1-x)17 are consistent with the magnetic anisotropy behavior of the single crystal. It is also shown that replacement of Co by Fe in Y2(FexCo1-x)17 proceeds with a preference.
TL;DR: In this paper, the effects of the biquadratic exchange interaction on the temperature dependence of the magnetic specific heat and sublattice magnetization have been calculated with the use of the spin wave theory for linear chain antiferromagnet.
Abstract: The effects of the biquabratic exchange interaction on the temperature dependence of the magnetic specific heat and sublattice magnetization have been calculated with the use of the spin wave theory for linear chain antiferromagnet. The antiferromagnetic spin structure changes abruptly and begins to make a cant at a certain ratio P c of the biquadratic exchange interaction to the Heisenberg one, which is reasonably small enough to appear in the real antiferromagnet with large spin. This change of the spin structure is shown to give significant effects on the magnetic properties.
TL;DR: In this paper, the electrical resistivity contribution from scattering of conduction electrons by Tb $4f$ electrons has been calculated in the paramagnetic regime in order to examine the competing effects of the crystal field and the exchange interaction.
Abstract: The electrical resistivity of ${\mathrm{Tb}}_{c}{\mathrm{Y}}_{1\ensuremath{-}c}\mathrm{Sb}$ has been measured as a function of temperature and of Tb concentration. The resistivity contribution from scattering of conduction electrons by Tb $4f$ electrons has been calculated in the paramagnetic regime in order to examine the competing effects of the crystal field and the exchange interaction. Excellent agreement with experiment is obtained for the entire range of $c$ with one value for each of the two adjustable parameters, the Fermi momentum, and the electron-ion exchange constant.
TL;DR: In this paper, the temperature dependence of the magnetic susceptibility (300 → 1.6°K) and ESR (300 − 6°K ) of amorphous germanium have been determined.
TL;DR: In this paper, the role of the interatomic exchange interaction in Ni-Co alloys has been investigated in order to explain the observed values of D. The experimental results seem to support that the contributions to the spin wave dispersion relation from the itinerant and localized characters of electrons are additive as shown by Englert et al and Yamada et al.
Abstract: Magnetization measurements of f. c. c. Ni-Co alloys using pendulum-type magnetometer have been made from liquid He temperature to room temperature. Magnetization vs temperature curves have been analyzed on the basis of the spin wave theory. The exchange integral J and the exchange stiffness constant D are estimated. The composition dependence of D is not consistent with that obtained by Hinoul et al . from spin wave resonance experiments nor with that obtained by Wakoh from the calculation on the basis of itinerant electron model. The experimental results seem to support that the contributions to the spin wave dispersion relation from the itinerant and localized characters of electrons are additive as shown by Englert et al . and Yamada et al . The role of the inter-atomic exchange interaction in Ni-Co alloys seems to be important in order to explain the observed values of D .
TL;DR: In this paper, the magnetic excitation spectrum of NdSb has been studied by neutron inelastic scattering and the experimental data are satisfactory described in terms of a cubic crystal field, an isotropic Heisenberg exchange and a large quadrupolar exchange interaction.
Abstract: The magnetic excitation spectrum of NdSb has been studied by neutron inelastic scattering. The experimental data are satisfactory described in terms of a cubic crystal field, an isotropic Heisenberg exchange and a large quadrupolar exchange interaction.
TL;DR: In this article, the authors examined the transport properties of the exchange interaction between carriers in a relatively wide band and localized magnetic moments, with special reference to the properties of europium compounds.
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01 Jan 1976
TL;DR: In this article, the connection between Equation of Motion Technique and Perturbation Theory Approach to the Evaluation of Double Time Green's function is discussed. But the authors do not discuss the application of double-time green's function to the analysis of magnetic properties of actinides.
Abstract: A Many Electron Theory of Localised Moments in Metals.- Magnetic Properties of a Dense Interacting Electron Gas.- Conceptual Phase Diagrams and Their Applications to Itinerant Electron Magnetism.- Narrow Band Magnetism of Alloys.- The Static and Dynamic Impurity Spin Susceptibility of Kondo Alloys.- Magnon Interaction in the Itinerant Electron Model of Ferromagnetism.- Studies of Ferro- and Paramagnetic Nickel by Positron Annihilation.- Theory of Magnetic Properties of Rare Earths and Their Compounds.- Exchange Interaction in the Heavy Rare Earth Metals Calculated from Energy Bands.- Lattice Effects and the Magnetic Behaviour of Rare Earth Compounds.- Elementary Excitations of High Degree Pair Interactions in Rare Earth Compounds.- Magnetic Properties of Actinides and Their Compounds.- Exploratory Band Structure Calculations for Actinide Compounds.- Magnetism in Actinides.- Thermodynamic Properties of the One-Dimensional Hubbard Model.- Weak Self-Consistent Approximation Scheme.- On the Connection between Equation of Motion Technique and Perturbation Theory Approach to the Evaluation of Double Time Green's function.- First Order Green Function Theory of a Heisenberg Ferromagnet.- Spin-One Lattice-Gas Model.- Dipolar and Quadrupolar Ordering in Magnetic Crystals.- One and Two Magnon Light Scattering in Insulating Antiferromagnets and Its Possible Relevance for the Investigation of the Short Range Interatomic Correlations.- Two-Fluid Hydrodynamic Description of Magnetic Crystals.- Impurity Ferromagnetism in Non-magnetic Semiconductors.- Phonon Hydrodynamics in Solids.- The Spin-Phonon Interaction in Anharmonic Ferromagnetic Crystals.- The Symmetry Properties of Magnetoelastic Waves and the Determination of Selection Rules for Magnon-Phonon Interactions.- Sound Absorption in Magnetics.- Contributors.
TL;DR: In this paper, the first nearest-neighbour exchange interaction was taken into account to calculate the electronic density of states in both the ferromagnetic and the paramagnetic phases of nickel-copper alloys.
Abstract: The coherent-potential approximation (CPA) has been employed to calculate the electronic density of states in both the ferromagnetic and the paramagnetic phases of nickel-copper alloys. The calculation takes into account in an approximate way the first nearest-neighbour exchange interaction, which is important in these alloys, the copper being nonmagnetic. The general satisfactory agreement with the available experimental data supports CPA as a good approach to the alloy problem.
TL;DR: In this article, exchange interaction between two 2 T 2g terms in Cs3Ti2Cl9 was studied. But the authors focused on the interaction between the two terms.
Abstract: (1976). Exchange interaction between two 2 T 2g terms in Cs3Ti2Cl9. Molecular Physics: Vol. 31, No. 3, pp. 957-961.
TL;DR: In this article, a single-ion hamiltonian was used to determine the energy level splitting within the F 5/2 ground state multiplet in the antiferromagnet CeP.
TL;DR: In this article, the frequency and temperature dependence of the linewidth of four solid organic radicals were investigated and the dipole-dipole interaction of the two nitroxide radicals included in this study was found to be temperature dependent, indicating changes in intermolecular spin separation with temperature.
Abstract: Investigations of the E.S.R. linewidths of exchange narrowed lines from solid organic free radicals allow one to obtain information about both the exchange interaction and the electron-electron dipolar interaction in some instances. In cases in which the dipolar interaction is incompletely averaged by spin exchange one can use the frequency dependence of the E.S.R. linewidth to determine the magnitudes of the exchange frequency and the dipolar interaction. This paper reports results from a study of the frequency and temperature dependence of the linewidth of four solid organic radicals. The dipole-dipole interaction of the two nitroxide radicals included in this study was found to be temperature dependent, indicating changes in intermolecular spin separation with temperature. The exchange energy of these two radicals appeared to vary exponentially with the separation of the spins through most of the temperature interval which was investigated.
TL;DR: In this article, the surface spin susceptibility of a nearly ferromagnetic metal was examined for the case of an exchange interaction with finite range and varying with the distance from the surface.
TL;DR: In this paper, a new infinite-order perturbation approach to the theory of spin waves in strongly anisotropic magnets is introduced, and the system is transformed into one with effective two-ion anisotropy and considerably reduced ground-state corrections.
Abstract: A new infinite-order perturbation approach to the theory of spin waves in strongly anisotropic magnets is introduced. The system is transformed into one with effective two-ion anisotropy and considerably reduced ground-state corrections. A general expression for the spin-wave energy, valid to any order, is given in terms of a renormalized exchange interaction and two anisotropy parameters. The relation between them and the fundamental parameters is given explicitly to second order. (AIP)