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Showing papers on "Exchange interaction published in 1984"


Journal ArticleDOI
TL;DR: In this article, the potential energy arises from the 4s conduction electron spin making a small angle with the local s−d exchange field, and a solution of the electron transport equations in the wall is obtained.
Abstract: Since the wall thickness is at least 102 electron wavelengths, a domain wall acts, through the s‐d exchange interaction, like a very weak and smooth potential barrier of height ≂10−2 eV, which does not reflect conduction electrons appreciably. The potential energy arises from the 4s conduction electron spin making a small angle with the local s‐d exchange field. Anisotropic s‐d exchange may also contribute to the potential barrier. A solution of the electron transport equations in the wall is obtained. In order for an electron current crossing the wall to exert an appreciable drive force on it, nonzero interband electron scattering by impurities or phonons is needed. The electron density for a given band varies slightly with location inside the wall, and depends on the current. Mutual electrostatic shielding between bands is taken into account. The drive force per unit wall area is F≂2Ms μ−1i (ve −vw), where ve and vw are electron drift speed and wall speed. In other words, this drive force at ve ≠0 is g...

474 citations


Journal ArticleDOI
TL;DR: In this article, the electrostatic and exchange interactions between two ground state 3Σ−g O2 molecules have been calculated ab initio by means of first order exchange perturbation theory, and the nonorthogonality problem has been handled in a second-quantized holeparticle formalism by a generalization of Wick's theorem.
Abstract: The electrostatic and exchange interactions between two ground state 3Σ−g O2 molecules have been calculated ab initio by means of first order exchange perturbation theory. The nonorthogonality problem has been handled in a second‐quantized hole‐particle formalism by a generalization of Wick’s theorem. The splitting between the spin states, S=0, 1, and 2, of the O2–O2 dimer is accurately represented by the Heisenberg Hamiltonian. By means of a spherical expansion for the orientational dependence and exponential functions for the distance dependence of the expansion coefficients, complete analytic potential surfaces have been evaluated, both for the spin‐independent term in the Heisenberg Hamiltonian ∼(ΔE) and for the exchange coupling parameter J. The strong anisotropy and distance dependence of J indicate that magnon–libron and magnon–phonon coupling in solid O2 are likely to be strong. A simple four‐electron model containing the O2 open shells only reproduces the structure dependence of J qualitatively, ...

101 citations


Journal ArticleDOI
TL;DR: In this article, the Brillouin-like function was used to obtain the s-d exchange constants in Zn 1−x Mn x Se : N o α = 0.26 eV, N o β = −1.31 eV.

85 citations


Journal ArticleDOI
TL;DR: In this article, the spin dynamics of weakly interacting, spin-polarized quantum gases are discussed in terms of a quasiparticle picture of these systems, and the theory is used to discuss magnetic resonance experiments in spin polarized atomic hydrogen.
Abstract: The spin dynamics of weakly interacting, spin-polarized quantum gases are discussed in terms of a quasiparticle picture of these systems. Quantum mechanical exchange between identical particles introduces "molecular" magnetic fields which give rise to the precession of the spin current; this in turn leads to coherent oscillations of the magnetization. The theory is used to discuss magnetic resonance experiments in spin-polarized atomic hydrogen.

53 citations


Journal ArticleDOI
TL;DR: Theoretical studies have investigated the temperature dependence of the magnetization at the surface of ferromagnets and it has become clear that surface anisotropy can significantly influence this temperature dependence.
Abstract: Theoretical studies have investigated the temperature dependence of the magnetization at the surface of ferromagnets. It has become clear that surface anisotropy can significantly influence this temperature dependence. For isotropic exchange uniform throughout the sample the temperature dependence of the magnetization varies as M(T)/M(0)≊(1−BT3/2) with a B factor at least twice as great as the bulk value. For cases in which the exchange interaction is weaker in the surface layer, or in which there is a significant surface exchange anisotropy a linear temperature dependence may result. These theoretical results have seen little experimental test. We report here measurements made on epitaxial (110) Fe films in which different temperature dependences are found depending upon the interfacial material chosen as a covering layer. The ferromagnetic films were made of 56Fe, permitting Mossbauer spectroscopic measurements of the magnetic hyperfine field of the surface alone by growing a surface layer of 57Fe. Thes...

51 citations



Journal ArticleDOI
TL;DR: In this paper, the majority and minority spin states of the exchange-split virtual bound state of Mn impurities in Cu and Ag are studied with high-resolution photoemission and bremsstrahlung isochromat spectroscopy.
Abstract: The majority- and minority-spin states of the exchange-split virtual bound state of Mn impurities in Cu and Ag are studied with high-resolution photoemission and bremsstrahlung isochromat spectroscopy. The exchange splitting is found to be close to the atomic value. The majority-spin state is strongly hybridized with the host-metal $d$ band resulting in its delocalization. The minority-spin states are localized but close to the Fermi level so that a description of the physical properties in terms of a spin Hamiltonian is not appropriate.

45 citations


Journal ArticleDOI
TL;DR: In a spin-polarized photoemission experiment as discussed by the authors, the escaping polarized electrons interact with a paramagnetic surface layer of variable thickness, and the exchange constant acting between the photoelectrons and the paramagnetic moments is obtained.
Abstract: In a spin-polarized photoemission experiment the escaping polarized electrons interact with a paramagnetic surface layer of variable thickness. From the depolarization of the photoelectrons the exchange constant acting between the photoelectrons and the paramagnetic moments is obtained.

41 citations


Journal ArticleDOI
TL;DR: In this article, the Curie temperature of a two-dimensional quadratic Ising ferromagnet with mixed spins of S = 1/2 and S =1 has been calculated with the use of Bethe-Peierls theory.
Abstract: For the two-dimensional quadratic Ising ferromagnet with mixed spins of S =1/2 and S =1, the Curie temperature T c has been calculated with the use of Bethe-Peierls theory. Assuming the bilinear exchange interactions J 1 between nearest neighbors (n.n.) of the different spins, J 2 and J 3 between two kinds of next nearest neighbors (n.n.n.) of the same spins, and the biquadratic exchange J 1 ′ between n.n. and J 2 ′ between n.n.n. of spins S =1, the behaviors of T c as a function of these exchange parameters are investigated. The ferromagnetic order is shown to be unstable when the ratio J 1 ′ / J 1 amounts to -1.85. It is also pointed out that J 1 ′ and J 2 ′ give a qualitatively different effect on T c . Furthermore, it turns out that the exchange interaction J 2 between n.n.n. of spins S =1 gives more significant effect on T c than J 3 between n.n.n. of spins S =1/2.

37 citations


Journal ArticleDOI
TL;DR: In this paper, the q 5 2 power law is well borne out at T = Tc, and strong zero-wavenumber relaxation due to spin nonconserving forces can make the predicted hydrodynamic spin diffusion at T > Tc unobservable.

33 citations


Journal ArticleDOI
TL;DR: In this article, magnetic susceptibility and specific heat data are presented on the S = 1 2 antiferromagnetic Heisenberg chain Cu(pyrazine) (NO 3 ) 2 in the range 0.05 K T.

Journal ArticleDOI
01 Apr 1984
TL;DR: In this article, a theory of near-resonant charge exchange (NRCE) in ion + molecule or molecular ion + atom collisions is presented and applied to the H 2 + + Mg collision at medium energies.
Abstract: A theory of near-resonant charge exchange (NRCE) in ion + molecule or molecular ion + atom collisions is presented and applied to the H 2 + + Mg collision at medium energies. The NRCE probabilities are obtained within the impact-parameter method (IPM) using the short collision time approximation (sudden transition for the nuclear motion in the molecule). The relevant exchange interactions are determined in the framework of the asymptotic theory of NRCE, using elementary linear combinations of atomic orbitals (ELCAOs) to describe the molecular orbital of the active electron that is captured to/from the molecule. The corresponding formulas appear as mere superpositions of ion + atom-like results and provide the full dependence of the exchange interaction upon the internal coordinates of the triatomic collision system. The application to the H 2 + + Mg collision deals with the dissociative charge exchange into the b 3 Σ u + (direct dissociation), the a 3 Σ g + (radiative dissociation) and the c 3 Π u (predissociation) states of H 2− . The treatment incorporates explicitly the charge-induced-dipole (a-b, c) and charge-quadrupole interactions in the highly polarizable outgoing channels considered. Results of the IPM close-coupling calculations for a few energies and diatom orientations are presented and compared with experiment.

Journal ArticleDOI
E. Kisker1
TL;DR: In this paper, the authors compared the results of a model calculation on the temperature-induced changes in the spin-resolved energy distribution curves, based on transverse fluctuations of microscopic regions of constant magnetic moments.

Journal ArticleDOI
Hideo Fukutome1
TL;DR: In this paper, a new microscopic theory for the electronic and lattice structures of crystal and defects of Se and Te was proposed, where electron correlation in valence P electrons produces a charge density wave (CDW) of vector nature, the vector CDW (VCDW), which has the period of three and keeps every atom neutral.
Abstract: A new microscopic theory is proposed for the electronic and lattice structures of crystal and defects of Se and Te. Consideration of the valence bond picture shows that electron correlation in valence P electrons produces a charge density wave (CDW) of vector nature, the vector CDW (VCDW), which has the period of three and keeps every atom neutral. Defects including valence alternation pairs and recombinations of helical chains may be generated as' low energy solitonic excitations of the VCDW. Amorphous Se and Te may be regarded as an assembly of solitonic excitations in the VCDW. A formulation of the VCDW and its soli tonic excitations is given in the HF approximation. Valence P electrons are described by an INDO type Hamiltonian with the nearest neighbour transfer and exchange interactions, intraatomic Coulomb repulsion and exchange and interatomic Coulomb repulsion. The remaining closed shell part of each atom is represented as a core with a repulsive potential. The lattice geometry is determined by the balance of the cohesive force of P electrons and the repulsion of cores. The effective intraatomic Coulomb interaction in a neutral atom has the form of a negative on-site interaction which stabilizes the VCDW. An equation is obtained which determines self-consistently the electronic and lattice structures of the VCDW and its solitonic defects. The VCDW and its defects always accompany not only an electron density modulation but also a bond order modulation so that they have lattice structures distorted from a standard cubic lattice. The trigonal lattice of the crystalline Se and Te can be explained as due to the presence of the VCDW.

Journal ArticleDOI
TL;DR: In this article, spin-flip Raman scattering, magnetization, and susceptibility data for Zn0.97Mn 0.03Se are reported, and the exchange energy Noα = 243 ± 10 meV for the conduction electrons is obtained from an analysis of the Raman and magnetization data.

Journal ArticleDOI
TL;DR: In this article, the Bethe-Peierls method was used to investigate the effect of higher-order exchange interactions on the Curie temperature of the two-dimensional quadratic Ising ferromagnetic of spin one, and the three-site four-spin interaction (Si.Sj)(Sj.Sk) was shown to give a more significant effect than the biquadratic exchange interaction and the bilinear exchange interaction between the next-neighbour spins.
Abstract: The effects of the higher-order exchange interactions of the type (Si.Sj)2 and (Si.Sj)(Sj.Sk) on the Curie temperature of the two-dimensional quadratic Ising ferromagnetic of spin one have been investigated with use of the Bethe-Peierls method. Apart from the dominant bilinear exchange interaction between the nearest-neighbour spins, the three-site four-spin interaction (Si.Sj)(Sj.Sk) is shown to give a more significant effect on the Curie temperature than the biquadratic exchange interaction and the bilinear exchange interaction between the next-nearest neighbour spins. When the ratio of the three-site four-spin interaction to the bilinear exchange interaction between the nearest-neighbour spins becomes -0.22 the ferromagnetic order is shown to disappear. The calculation has been extended to the case of a simple cubic Ising ferromagnet, and the three-site four-spin interaction is also shown to be significant with the critical ratio -1.17, which is compared with -0.22 of the quadratic Ising ferromagnet. The origin of the three-site four-spin interaction has also been discussed by taking into consideration the magnetoelastic effect and perturbation expansion.

Journal ArticleDOI
TL;DR: In this paper, the effect of exchange interaction with magnetic ions on the electron band structure is considered and exchange splitting of donor states, and of acceptor states in wide-gap DMS is discussed, as well as the boil-off of acceptors in narrow gap DMS due to exchange interaction.

Journal ArticleDOI
TL;DR: In this article, it was shown that in those alloys in which the linear chains of magnetic atoms are not disturbed, the exchange coupling constants become positive leading to ferromagnetic coupling when the distance between Mn atoms becomes equal to 2.83 A or more.

Journal ArticleDOI
TL;DR: In this paper, quantum mechanical calculations of the differential, momentum transfer, and integral cross sections for electron-CH4 elastic scattering in the energy range 20-500 eV were presented.
Abstract: We report quantum mechanical calculations of the differential, momentum transfer, and integral cross sections for electron‐CH4 elastic scattering in the energy range 20–500 eV. The e−‐CH4 interaction term is composed of three local spherical potentials, namely, the static, the exchange, and the polarization. The static potential is generated without additional approximations from near‐Hartree–Fock methane wave functions; the exchange interaction is included in the free‐electron‐gas‐exchange (FEGE) model; and for polarization, we employ a parameter‐free ab initio potential of Jain and Thompson. All the cross sections are in good accord with recent absolute experiments.

Journal ArticleDOI
TL;DR: In this paper, the phase diagram of the stable states in the presence of the magnetic field is obtained for the quasi-one-dimensional Heisenberg antiferromagnet coupled with the lattice distortion.
Abstract: The phase diagram of the stable states in the presence of the magnetic field is obtained for the quasi-one-dimensional Heisenberg antiferromagnet coupled with the lattice distortion. The spin-flop state and the state having spin-solitons appear as the possible ground states besides the spin-Peierls state and the Neel state which are the ground state in the absence of the magnetic field. Three types of field-induced phase transitions are shown to exist depending on the relative strength of the weak interchain exchange interaction to the spin-lattice coupling.

Journal ArticleDOI
TL;DR: In this paper, first principles calculations of spin and angle-resolved photoemission spectra for Fe(100) at T = 0 and T = T c, based on the KKRCPA treatment of the disordered local moment model, are presented.

Journal ArticleDOI
TL;DR: In this paper, a non-collinear spin arrangement escorted with a crystallographic distortion was observed in the terbium iron garnet: Tb3Fe5O12 at low temperature.

Journal ArticleDOI
TL;DR: The 3s-3p impact excitation of spin-polarised Na atoms by unpolarised electrons has been studied in this paper, where the fluorescence light emitted in the decay of the excited state exhibits linear polarisation caused by collisional induced 3p alignment, as well as circular polarisation resulting from the spin orientation of the 3p electron at the time of decay.
Abstract: The 3s-3p impact excitation of spin-polarised Na atoms by unpolarised electrons has been studied. The fluorescence light emitted in the decay of the excited state exhibits linear polarisation caused by the collisional induced 3p alignment, as well as circular polarisation resulting from the spin orientation of the 3p electron at the time of the decay. Since the exchange interaction causes a spin flip, the degree of circular light polarisation is a measure for the contribution of the exchange channel to the total excitation cross section. At small impact energies where exchange becomes important, the authors found a decrease of the circular polarisation. They analysed the hyperfine coupling between the excited electron and the polarised nucleus, and calculated the light polarisation from theoretical excitation cross sections. Comparison of experiment and theory shows reasonable agreement.

Journal ArticleDOI
TL;DR: In this paper, the dependence of the exchange integral upon homogeneous deformations in the first and second order is taken into account, and correlated equations of state for magnetic and elastic ferromagnetic subsystems are obtained.

Journal ArticleDOI
TL;DR: In this article, a relativistic multiple scattering theory for low-energy electron diffraction (LEED) from ferromagnets has been extended to allow for arbitrary magnetisation orientation and to take account of thermal lattice vibrations.
Abstract: A fully relativistic multiple scattering theory for low-energy electron diffraction (LEED) from ferromagnets has been extended to allow for arbitrary magnetisation orientation and to take account of thermal lattice vibrations. Time-reversal and spatial symmetries were used to derive general results and to reduce the computational labour. Numerical results are presented for the ferromagnetic surfaces Ni(001), Fe(110) and Gd(0001). The exact spin-orbit and exchange-induced scattering asymmetries are found to be excellently approximated by spin-orbit-only and exchange-only asymmetries as well as by experimentally more convenient asymmetries in the cases of Ni and Fe, and more moderately so in the case of Gd. A new type of scattering asymmetry, which is brought about by an interplay between spin-orbit and exchange interaction already for unpolarised primary electrons, is predicted to reach sizeable values (up to about 40% for Gd) and to respond very sensitively to assumed changes in the magnetisation of the top layer. This suggests, firstly, the feasibility of studying surface ferromagnetism by unpolarised LEED and, secondly, an enhanced accuracy and reliability when using polarised electrons.

Journal ArticleDOI
TL;DR: The ground state of the holmium ion in ferromagnetic HoAl2 is discussed in the light of available experimental evidence, including hitherto unpublished NMR measurements on165Ho as discussed by the authors.
Abstract: The ground state of the holmium ion in ferromagnetic HoAl2 is discussed in the light of available experimental evidence, including hitherto unpublished NMR measurements on165Ho. The measured quadrupole splitting is not consistent with the ground state derived from neutron form factor experiments, but is compatible with exchange and crystal field parameters derived from magnetization measurements and neutron spectroscopy in the context of the conventional three-parameter mean-field model. A more detailed analysis of the NMR data indicates that the exchange interaction in HoAl2 is over 20% stronger than that derived, using mean-field theory, from the Curie temperature. Using the revised exchange constant and a weighted average of published crystal field parameters, we obtainμ = (9.39 ± 0.05)μ B for the moment on the Ho3+ ion atT =0. The contribution of orbitally polarized conduction electrons to the hyperfine field at the holmium nucleus is estimated to be (−1.4±2.0) T.


Journal ArticleDOI
TL;DR: In this paper, the stability of ferromagnetic systems in intermediate valence systems which fluctuate between a magnetic (J≠0) and a non-magnetic (J=0) state as e.g. EuO was studied.
Abstract: We study the stability of ferromagnetism in intermediate valence systems which fluctuate between a magnetic (J≠0) and a non-magnetic (J=0) state as e.g. EuO. We consider thes-f model extended by a hybridization term as a good description of the normal valence as well as the intermediate valence phase of such materials. Special attention is devoted to the competing influence ofs-f exchange ands-f hybridization on the Curie temperatureTc. For large gaps between the localizedf-level and the conduction band (normal valence phase!)s-f exchange ands-f hybridization both tend to stabilize magnetism giving rise to an effective exchange interaction betweenf-moments. This effective exchange increases with decreasing gap leading to a substantialTc-enhancement for small gaps. In the intermediate valence phase, however, electronic fluctuations destroy the collective magnetism, and that twofold, namely by reducing the local magnetic moment and by enhancing entropy-influences. The latter leads toTc→0, therewith determining the boundary between the ferromagnetic and paramagnetic phase. A corresponding phase diagramm, in dependence of hybridizationV andf-level positionEf, is derived and discussed.

Journal ArticleDOI
TL;DR: In this paper, it was shown that the Cd 1-x Mn 2+ exchange interaction is responsible for the field and temperature dependence of the polarization in the presence of a weak magnetic field.

Journal ArticleDOI
TL;DR: In this paper, the single-crystal gadolinium dielectric permeability spectrum was investigated experimentally and theoretically in the frequency range 0.5 ⩽ h ω ⩾ 1 eV in terms of intra-atomic light absorption and the magnetic order parameter dependence of the coherence degree of angular parts of quasi-bound 5d-electron wave functions.