Showing papers on "Exchange interaction published in 1979"
TL;DR: The phase diagram of the Kondo lattice was discussed in this paper, where the authors generalize to the lattice a method proposed by Yoshimori and Sakurai for the single-impurity Kondo problem.
Abstract: We discuss the phase diagram of the Kondo lattice: we generalize to the lattice a method proposed by Yoshimori and Sakurai for the single-impurity Kondo problem; this method transforms the Kondo exchange interaction into a fictitious $s\ensuremath{-}f$ hybridization, and gives a resonance of width ${T}_{K}$ at the Fermi level. We study the Kondo phase and compare its energy with the energy of the magnetic phase. The Kondo state is stable when the exchange interaction is larger than a critical value; this state is insulating when the conduction band is half filled.
220 citations
TL;DR: In this article, a large body of data is reviewed, which illustrates how the high pressure technique can be used to gain information about the magnetic and electronic state of dilute magnetic alloys.
Abstract: A large body of data is reviewed, which illustrates how the high pressure technique can be used to gain information about the magnetic and electronic state of dilute magnetic alloys. Values for the pressure dependence of the elementary effective exchange interaction between a magnetic impurity spin and the conduction electron sea are extracted from the data and tabulated for a number of extremely dilute alloys containing both transition metal and rare earth impurities. Results of experiments on host alloy series employing ‘lattice pressure’ are compared to the present ‘external pressure’ results and critically analysed; it is shown how such a comparison can be used to give information about the extent of the electronic screening around an impurity potential. The effect of pressure on impurity-impurity interactions in spin glasses is also examined; a comparison of the pressure studies on extremely dilute alloys to those on spin glasses allows an estimate of the nature of the interaction mechanisms...
93 citations
IBM1
TL;DR: In this article, the systematics of the Fe-Fe exchange in amorphous rare-earth---Fe alloys, without the complications associated with the magnetic characteristics of the rare earth elements, have been prepared with a wide range of Fe concentrations.
Abstract: In order to study the systematics of the Fe-Fe exchange in amorphous rare-earth---Fe alloys, without the complications associated with the magnetic characteristics of the rare-earth elements, amorphous films of Fe alloyed with La, Lu, Y, and Zr have been prepared with a wide range of Fe concentrations. Magnetization and M\"ossbauer-effect measurements were made. The magnetic properties of the alloys depended critically on the choice of rare earth (or rare-earth-like element). YFe and LuFe alloys were found to have spin-glass characteristics while LaFe and ZrFe alloys were found to be ferromagnetic, but with evidence that exchange fluctuations were nearly as large as the average exchange. Thus the nature of the Fe-Fe exchange interaction depends critically upon the species of the rare earth. The most important parameter in determining the magnetic behavior of these alloys appears to be the size of the rare-earth atom, with large rare-earth atoms resulting in a smaller ratio of exchange fluctuations to exchange. The same dependence of the magnetic properties upon rare-earth size appears to be important in the case of magnetic-rare-earth atoms; however, the effect of rare-earth---Fe exchange also becomes important and these effects are discussed.
56 citations
TL;DR: In this paper, a relativistic generalisation of the Bloch theory of a magnetic electron gas was presented, and it was shown that states of uniform magnetisation as in the non-relativistic theory do not appear as ground states in the Hartree-Fock approximation including transverse photon contributions.
Abstract: The authors present a relativistic generalisation of the Bloch theory of a magnetic electron gas. It is shown that states of uniform magnetisation, as in the non-relativistic theory, do not appear as ground states in the Hartree-Fock approximation including transverse photon contributions. The exchange energy changes sign for certain values of the relativistic parameter ( beta =h(cross)kF/mc) and magnetisation so that spiral spin arrangements may be favoured.
47 citations
TL;DR: In this article, the Hohenberg-Kohn theorem is generalized to unrestricted Hartree-Fock (UHF) wave functions, and it is shown that the UHF wave function functional ψ[ρ] exists for all such densities.
Abstract: The Hohenberg–Kohn theorem is generalized to unrestricted Hartree–Fock (UHF) wave functions. It is postulated that each N‐electron density can be expanded in many sets of orbitals, and these orbital sets are continuously deformable into one another. Subject to these postulates several conclusions follow: The UHF wave function functional ψ[ρ] exists for all such densities. It consists of those orbitals which minimize the sum of kinetic and exchange energies, and it can always be chosen to be a ground state wave function. The exact exchange energy, including self‐repulsion, is also a functional of the electron density. It is implicitly defined as the expectation value of exchange energy for the wave function functional ψ[ρ]. This work also addresses some general properties of local exchange potentials. A local exchange potential is a multiplicative potential which replaces the exchange operator in the UHF equations. Every method which employs a local exchange potential is variationally equivalent to minimiz...
45 citations
TL;DR: Mossbauer measurements were made on the disordered binary alloys Ni3Fe NiFe and FeCo at different temperatures and the distribution of hyperfine magnetic fields has been evaluated using a model-independent method of analysis proposed by Window as discussed by the authors.
Abstract: Mossbauer measurements were made on the disordered binary alloys Ni3Fe NiFe and FeCo at different temperatures and the distribution of hyperfine magnetic fields has been evaluated using a model-independent method of analysis proposed by Window (1971). The full width at half-maximum of the P(H) distribution is found to remain constant for Ni3Fe with respect to temperature. It increases for NiFe but decreases for FeCo with increase of temperature. The full width at half-maximum is correlated to the exchange interaction and the measurements show that the range of exchange interaction is shorter in NiFe than in Ni3Fe. In FeCo all the atoms are found to have the same magnetic ordering temperature. The reduced value of the average field for NiFe is fitted to the Brillouin function.
32 citations
15 Sep 1979
TL;DR: In this article, the temperature dependence of the magnetic susceptibility of the title compound was studied in the range 3.6-300 K. The experimental data were interpreted with a hamiltonian taking into account the distorsion and the spin-orbit coupling around the Co(II) ion on one hand, and the Cu(II)-Co( II) interaction on the other.
Abstract: The temperature dependence of the magnetic susceptibility of the title compound was studied in the range 3.6–300 K. This heterobinuclear complex may be considered as the simplest polynuclear system in which the problem of the orbital degeneracy occurs. The experimental data were interpreted with a hamiltonian taking into account the distorsion and the spin-orbit coupling around the Co(II) ion on one hand, and the Cu(II)-Co(II) interaction on the other. From this hamiltonian, a quite satisfying simulation of the experimental magnetic curve was obtained. The effective exchange interaction parameter J of the −JSCu SCo term of the hamiltonian was found equal to =62 ± 2 cm−1. This value was compared to those obtained with the [CuCu], [CuNi] and [CuMn] complexes prepared with the same bichelating ligand. This comparison was carried out in a framework of an orbital model, previously established in the case of interacting ions without orbital momentum and here extended to the case where one of the interacting ions has an orbital degeneracy.
31 citations
TL;DR: In this paper, the first order electrostatic and exchange interaction energies in H2O-H2O and H 2O*−Ne dimers were calculated and correlated with the spatial distribution of the Rydberg state.
Abstract: In order to interpret the solvation blue shift in the 1A1→1B1 UV band in H2O (observed in liquid water, ice, and H2O embedded in rare gas matrices) we have made ab initio calculations of the first order electrostatic and exchange interaction energies in H2O–H2O and H2O*–Ne dimers, after extending the usual symmetry adapted perturbation expressions to excited state molecules.We have found this blue shift to be caused mainly by the enlarged exchange repulsion between the excited H2O molecule and its neighbors, originating from the extended (Rydberg) character of the excited 1B1 state. The orientational dependence of this exchange repulsion has been calculated and correlated with the spatial distribution of the Rydberg state. The transition‐dipole resonance interaction was found to be of little importance. These results were confirmed by supermolecule MO calculations on the ground state and excited dimers which showed moreover, an enlarged polarization of the excited H2O ( compared with the ground state), as...
31 citations
TL;DR: In this paper, the magnetic field dependence of the E.S.R. linewidth in amorphous silicon has been measured in order to investigate the influence of the exchange interaction on the magnetometer.
Abstract: The magnetic-field dependence of the E.S.R. linewidth in amorphous silicon has been measured in order to investigate the influence of the exchange interaction on the E.S.R. linewidth. A different field dependence was obtained for amorphous silicon prepared by the glow-discharge technique and by electron-beam evaporation. The experimental results are discussed in terms of exchange-coupled spins which are distributed either homogeneously or inhomogeneously. It is concluded that exchange interaction is necessary to account for a variety of experimental results obtained in these materials.
26 citations
TL;DR: In this paper, the first order phase transition observed in alkali-TCNQ salts is explained by the spin-lattice interaction caused by the modulation of the exchange interaction due to lattice distortion.
Abstract: The dimerization phase transition of alkali-TCNQ salts has been studied from the standpoint of the localized electron system. The one-dimensional antiferro-magnetic Heisenberg model is used. In this model the spin-lattice interaction is caused by the modulation of the exchange interaction due to lattice distortion. Within the Hartree-Fock and adiabatic approximations, the displacement, specific heat, and susceptibility are calculated as functions of temperature. The first order phase transition observed in alkali-TCNQ salts is explained by this theory. Finally, the dimerization phase transition of the Ising chain is studied to discuss the effect of the anisotropy of the exchange interaction on the structural phase transition.
26 citations
TL;DR: The contribution of phonons to the Hubbard-type exchange interaction parameter is shown to be much smaller than the electron-phonon massenhancement parameter as a consquence of Migdal's theorem as mentioned in this paper.
Abstract: The contribution of phonons to the Hubbard-type exchange interaction parameter is shown to be much smaller than the electron-phonon mass-enhancement parameter $\ensuremath{\lambda}$ as a consquence of Migdal's theorem. Application to Zr${\mathrm{Zn}}_{2}$ and the connection with $p$-state pairing are briefly discussed.
TL;DR: Amorphous (FexMo1−x)75P16B6Al3 with x=0.7 and x = 0.2 have been studied by 57Fe Mossbauer spectroscopy as mentioned in this paper.
Abstract: Amorphous (FexMo1−x)75P16B6Al3 with x=0.7, 0.8, 0.9, 0.95 and 1.0 have been studied by 57Fe Mossbauer spectroscopy. The magnetic ordering temperature decreases drastically from 640 K for x = 1.0 to 26 K for x = 0.7. The result suggests an antiferromagnetic exchange interaction between Fe and Mo. Anomalous magnetic hyperfine interactions have been observed at 4.2 K. The P(H) analyses indicate a two‐maxima function of H. The intensity of the low‐field component increases with Mo content and at the expense of the high‐field component. This indicates that there is a substantial number of Fe atoms which are weakly magnetic or have small moments.
TL;DR: The magnetic susceptibility of NaCeS2 has been measured between 3.7 and 297 K by the Faraday method as discussed by the authors, and the high temperature region (T > 150 K) shows Curie-Weiss behavior.
Abstract: The magnetic susceptibility of NaCeS2 has been measured between 3.7 and 297 K by the Faraday method. In this compound cerium has the oxidation state +3. Below 4.8 K, antiferromagnetic ordering exists. Only the high temperature region (T > 150 K) shows Curie-Weiss behavior. Below 150 K large deviations from the Curie-Weiss straight line are present. Cubic crystal field splitting in the J = 5 2 ground state of Ce3+ and isotropic exchange alone do not explain the data in the paramagnetic region, but an extended molecular field model, which takes into consideration different exchange interaction parameters for the Γ7 and Γ8 crystal field states, gives good agreement between the measured and calculated susceptibility values.
TL;DR: The energy of exchange repulsion between two closed-shell systems described by determinantal wave functions has been represented as a sum of contributions arising from the interaction of two, three and four orbitals at a time.
Abstract: The energy of exchange repulsion between two closed-shell systems described by determinantal wave functions has been represented as a sum of contributions arising from the interaction of two, three and four orbitals at a time. These contributions have been calculated for the interaction of two neon atoms. It has been found that in the van der Waals minimum region the two-orbital components are of secondary importance and that about 90% of the total exchange energy originates from the three-orbital interactions ofL-shell electrons. The four-orbital as well as the double-exchange terms have been found negligible. The approximate algorithms for evaluation of the exchange repulsion energy have been tested and discussed.
TL;DR: In this article, the spin wave energy dispersion in the (010) plane of the distorted perovskite KCuF3, which exhibits many magnetic properties of the spin-1/2 one-dimensional antiferromagnet, has been investigated at 4.7K (TN=39K).
Abstract: Using inelastic neutron scattering techniques, the spin wave energy dispersion in the (010) plane of the distorted perovskite KCuF3, which exhibits many magnetic properties of the spin-1/2 one-dimensional antiferromagnet, has been investigated at 4.7K (TN=39K). The measurements confirm the very strong exchange interaction between the spins in the (001) direction, and show that in this direction the expression for the excitation energies of the spin-1/2 antiferromagnetic chain given by des Cloizeaux and Pearson (1962) is obeyed. The exchange interaction between these chains is found to be only 1.6% of that within the chains.
TL;DR: In this paper, it was shown by small-angle neutron scattering that the magnetic structure of Invar alloys in the ground state is characterized by the occurrence of static magnetic fluctuations on the scale of 10-12 A. These fluctuations are due to antiferromagnetic iron pair interactions.
TL;DR: This paper analyzed the Mossbauer spectra for amorphous Fe78B12Si10 at several temperatures and found that the exchange interactions in this and other similar transition metal-metalloid alloys are predominantly long range; that is, although the hyperfine field distribution is broad, the exchange interaction distribution is narrow.
TL;DR: In this paper, the magnetocrystalline anisotropy in Co, YCo5, GdCo5 and SmCo5 was analyzed using a single-ion crystal field and isotropic exchange interaction.
Abstract: Experimental data on the magnetocrystalline anisotropy in Co, YCo5, GdCo5, SmCo5 and Y2Co17 is analysed using a single-ion crystal field and isotropic exchange interaction. The large magnetic anisotropy at high temperatures in the alloys is due to significant deviations in the alloy lattices of the ratio c/a from the ideal square root (8/3) ratio.
TL;DR: In this paper, the authors compared the Curie temperature of Fe80P20 and Fe80B20 with 57Fe Mossbauer spectroscopy and concluded that both the mean exchange interaction (J0) and the width (ΔJ) of the distribution of exchange interactions are considerably smaller in Fe 80P20 compared to Fe 80B20.
Abstract: Binary amorphous Fe80P20 has been studied by 57Fe Mossbauer spectroscopy. The results from this study are compared with those of Fe80B20 so that the influence due to the metalloid elements can be elucidated. The Curie temperature of TC=580 K for Fe80P20 is considerably lower than that of 685 K for Fe80B20. The hyperfine field distribution {P(H) } of Fe80P20 is distinctively asymmetrical as opposed to a nearly symmetrical P(H) in Fe80B20. From the temperature dependence of the hyperfine field and the values of TC we have concluded that both the mean exchange interaction (J0) and the width (ΔJ) of the distribution of exchange interactions {P(J) } are considerably smaller in Fe80P20. A large difference in the isomer shift has also been observed in the two alloys. It is suggested that these large changes are in part caused by the electronic differences of phosphorus and boron. At high temperatures Fe80P20 crystallizes into Fe3P and α‐Fe.
TL;DR: In this article, a new method has been developed at Osaka University for producing a mega-gauss field without destruction of the coil, and the effect of high field effects was reported in submillimeter ESR experiments.
Abstract: A new method has been developed at Osaka University for producing a mega‐gauss field without destruction of the coil. As one of the applications of this system, submillimeter ESR experiments have been done at low temperatures by using HCN (λ=337μm) and H2O (λ=119μm) lasers in a field up to 0.5 MOe. We report some novel high field effects observed in these experiments. The g‐shift due to the SH3 term is expected to be appreciable in such a high magnetic field. This effect was found in a study of Co‐Tutton salt at 77 K. The experimental result showed 2% smaller g value at 119 μm than at 337 μm. This was explained quantitatively by an extensive calculation based on the Abragam‐Pryce theory. So‐called exchange splitting was observed in (NH4) 2CuCl4⋅2H2O, Cu(NH3) 4SO4⋅H2O (CTS) and CuCl2⋅2H2O. At 4.2 K the two observed lines were of quite different intensities and the weaker one showed a remarkable shift. These phenomena can be explained successfully by molecular field theory, and it is shown from the direction of the shift that the exchange interaction between inequivalent spins is antiferromagnetic for CTS and ferromagnetic for the others.
TL;DR: In this article, the authors developed the technique of determining the magnetic structures liable to occur in a crystal by analyzing the exchange Hamiltonian, based on Bertaut's idea that the exchange matrix eigenfunction corresponds to some magnetic structure.
TL;DR: In this article, the rotational energy transfer induced in an openshell molecule by collision with an open-shell atom is investigated and related to the behaviour of unpaired electron spins during inelastic collisions.
Abstract: The theory is developed for the rotational energy transfer induced in an open-shell molecule by collision with an open-shell atom. The consequences of the exchange interaction between such systems are investigated and related to the behaviour of unpaired electron spins during inelastic collisions. The coupled equations for the closed shell case are first developed, and generalized equations derived for the matrix elements of a spin-independent potential. The spin-exchange interaction potential of openshell species is then expressed in a form suitable for scattering theory and this leads to coupling matrix elements in a basis which includes electron spin. Nuclear spin is also included by a simple extension of the basis set. It is then argued that many open-shell collisions leading to rotational energy transfer will be sufficiently weak that the coupled equations can be treated by use of the restricted distorted-wave. Born approximation. This method leads to the derivation of expressions for scattering cross-sections in both the spin-independent and spin-correlated cases. The influence of exchange forces is manifest in branching fractions for spin multiplets, which relate the cross-sections for the different $\Delta J$ associated with each change in rotational quantum numbers. A general expression for the branching fractions in hyperfine multiplets is also derived. The discussion deals with the extent to which exchange forces will influence rotational energy transfer in practice. It shows how the results of experimental investigations such as those in the following paper might be interpreted. The way in which rotational propensity rules may be affected by exchange interactions is illustrated by reference to the model systems H + CN and H + NH$_{2}$. In conclusion it is noted that open-shell open-shell collisions take place naturally both in the upper atmosphere and in interstellar space.
TL;DR: In this paper, the crystal-field and exchange parameters of SmN have been deduced from the results of diffraction experiments, which allow a consistent interpretation of all the experimental results.
TL;DR: In this paper, the effects of the biquadratic exchange interaction and the uniaxial anisotropy on the Curie temperature of the ferromagnetic spin system of spin one with anisotropic exchange interaction have been calculated with the use of the pair model approximation.
Abstract: The effects of the biquadratic exchange interaction and the uniaxial anisotropy on the Curie temperature of the ferromagnetic spin system of spin one with anisotropic exchange interaction have been calculated with the use of the pair model approximation. The dependence of the Curie temperature on the biquadratic exchange interaction and on the uniaxial anisotropy have been calculated for crystal lattices of different coordination numbers and for spin systems of various anisotropy parameters of the exchange interaction and discussed in comparative way. In a certain range of the anisotropy parameter of the exchange interaction, the biquadratic exchange interaction is shown to have no effect on the Curie temperature.
TL;DR: In this paper, the influence of the exchange interaction on electron bands and electrical resistivity is studied, valid up to the region where the level broadening exceeds the average thermal energy but is small compared to the bandwidth.
Abstract: In the $s\ensuremath{-}f$ model electrons in the conduction band are coupled with the lattice of localized magnetic moments by exchange interaction. In this paper the influence of the exchange interaction on electron bands and electrical resistivity is studied. An intermediate-coupling theory is presented, valid up to the region where the level broadening exceeds the average thermal energy but is small compared to the bandwidth. Using the functional-derivative method the spin correlations are expressed in terms of the connected correlation functions. The functional-derivative method also provides a decoupling recipe for the electron Green's functions. Concentrating on the two-spin correlations the single-particle Green's function is derived by a decoupling method and is shown to be equivalent to a perturbation expansion. The finite lifetime is obtained for all band energies. The absorption edge, derived from density of states, shows in ferromagnetic semiconductors the familiar red shift and in addition a blue shift of magnetic origin in the paramagnetic region. Mobility is derived from the two-particle Green's function calculated by a decoupling method. Level broadening affects both the acceleration and the scattering part, resulting generally in smaller mobilities than predicted by the weak-coupling theory. In addition, corrections to the ordinary acceleration term are obtained. Results for the ferromagnetic semiconductors EuS and EuO are presented. The narrow mobility minimum occurring at ${T}_{C}$ in the weak-coupling case is considerably broadened in temperature. The minimum mobilities are around 3 ${\mathrm{cm}}^{2}$/Vsec in both materials. The low mobility near ${T}_{C}$ is partly caused by the intense scattering and partly by the decrease in the acceleration term. The results compare reasonably well with experiments.
TL;DR: In this paper, the Luttinger model with additional Heisenberg type Hamiltonian for free carriers-Mn ions exchange interaction was used to explain the strong influence of the exchange interaction on the positions of magnetotransmission minima.
TL;DR: In this paper, a theory of superconductivity for metals in which there are localized spins is presented, and the spins interact with the conduction electrons via an exchange interaction and with one another via a direct Heisenberg interaction, as well as indirectly via conduction electron.
Abstract: In this paper a theory of superconductivity for metals in which there are localized spins is presented. The spins interact with the conduction electrons via an exchange interaction and with one another via a direct Heisenberg interaction, as well as indirectly via the conduction electrons. The spins are treated as classical vectors in a mean-field approximation. The superconducting pair-breaking mechanism is treated in the approximation of Abrikosov and Gor'kov. Complete interplay of magnetization and pair-breaking processes is taken into account. Phase diagrams are presented. A treatment of alloys of two different magnetic ions is included in a simple approximation. All results are in good qualitative agreement with the experiment.
TL;DR: For a spin one-half Ising ferromagnet with two-dimensional quadratic lattice, the effects of the apparent three spin interaction, which is reduced effectively to the bilinear exchange interaction between next nearest neighbors, on the Curie temperature, magnetization and the magnetic specific heat have been calculated with the use of Bethe-Peierls theory as mentioned in this paper.
Abstract: For a spin one-half Ising ferromagnet with two-dimensional quadratic lattice, the effects of the apparent three spin interaction, which is reduced effectively to the bilinear exchange interaction between next nearest neighbors, on the Curie temperature, magnetization and the magnetic specific heat have been calculated with the use of Bethe-Peierls theory. The ferromagnetic order is shown to become unstable when the ratio of the three spin interaction to the bilinear exchange interaction amounts to -1/3. Also it is pointed out that the three spin interaction gives significant changes on the Curie temperature and on the temperature dependences of the magnetization and the magnetic specific heat.
TL;DR: The dependence on distance of the exchange integrals J was investigated for the first and second nearest Cr3+-pairs in ruby by uniaxial pressure along the C3-axis as mentioned in this paper.