scispace - formally typeset
Search or ask a question

Showing papers on "Exchange interaction published in 1991"


Journal ArticleDOI
TL;DR: It is shown that Co slabs are indirectly exchanged coupled via thin Cu layers with a coupling that alternates back and forth between antiferromagnetic and ferromagnetic superlattices, confirming theoretical predictions more than 25 years old.
Abstract: Confirming theoretical predictions more than 25 years old, we show that Co slabs are indirectly exchange coupled via thin Cu layers with a coupling that alternates back and forth between antiferromagnetic and ferromagnetic Four oscillations are observed with a period of \ensuremath{\simeq}10 \AA{} Moreover, the antiferromagnetically coupled Co/Cu superlattices exhibit extraordinarily large saturation magnetoresistances at 300 K of more than 65%

1,141 citations


Journal ArticleDOI
Stuart S. P. Parkin1
TL;DR: The exchange-coupling strength is found to increase systematically from the 5d to 4d to 3d metals and exponentially with increasing number of d electrons along each period.
Abstract: We show that oscillatory indirect magnetic exchange coupling via transition metals sandwiched between ferromagnetic layers of Fe, Co, Ni, or Ni alloys is a general phenomeonon. Surprisingly, the oscillation period is approximately the same, \ensuremath{\simeq}10 \AA{}, in all the transition metals in which we observe coupling with the single exception of Cr, for which it is much longer. Furthermore, the exchange-coupling strength is found to increase systematically from the 5d to 4d to 3d metals and exponentially with increasing number of d electrons along each period.

902 citations


Journal ArticleDOI
TL;DR: From atomic calculations in crystal-field symmetry, a very strong circular and linear dichroism in the 2p x-ray absorption edges of magnetically ordered 3d transition-metal ions is found, providing a basis for the study of magnetic x-rays dichroISM on materials with localized 3d electrons.
Abstract: From atomic calculations in crystal-field symmetry we find a very strong circular and linear dichroism in the 2p x-ray absorption edges of magnetically ordered 3d transition-metal ions. The spectral shape changes drastically with the character of the ground state, which is determined by the presence of a crystal field, and the relative magnitudes of the exchange and 3d spin-orbit interaction. The difference in integrated intensity of the 2p absorption for left- and right-circular polarization provides a measure for the 3d spin-orbit coupling in spherical and crystal-field symmetry. The anisotropic branching ratio depends on the spin-orbit interaction and the Van Vleck contribution of the exchange interaction. The results of our calculations provide a basis for the study of magnetic x-ray dichroism on materials with localized 3d electrons.

380 citations


Journal ArticleDOI
J. C. Slonczewski1
Abstract: We show how spatial fluctuations of chromium thickness amounting to one atomic monolayer account phenomenologically for the biquadratic magnetic coupling recently reported in epitaxial Fe/Cr/Fe trilayers. Corresponding fluctuations of the short-period oscillatory term of conventional exchange coupling induce static waves of magnetization whose energy has the observed biquadratic form. An existing calculation of conventional exchange and its recent direct measurements in highly ordered trilayers support our interpretation.

341 citations


Journal ArticleDOI
TL;DR: A close analogy between oscillations in the exchange coupling and de Haas-van Alphen oscillations is established and exploited to show that the period, asymptotic decay, and temperature dependence of the oscillations are determined by properties of the Fermi surface in the spacer layer.
Abstract: A theory of oscillations in the exchange coupling between two transition-metal ferromagnets separated by a nonmagnetic transition-metal spacer is developed for a one-band model. A close analogy between oscillations in the exchange and de Haas--van Alphen oscillations is established and exploited to show that the period, asymptotic decay, and temperature dependence of the oscillations are determined by properties of the Fermi surface in the spacer layer. The theory describes many features of the oscillations in the exchange coupling observed recently in Co/Ru, Co/Cr, and Fe/Cr superlattices.

336 citations


Journal ArticleDOI
TL;DR: In this article, it was shown that when the magnetostatic energy is small compared to the exchange energy, the resonance modes are a quadratic function of the reciprocal size.
Abstract: Magnetostatic resonance modes are usually calculated by assuming that the exchange energy is negligible compared to the magnetostatic energy. It is shown that in the other extreme, when the magnetostatic energy is small compared to the exchange energy, the resonance modes are a quadratic function of the reciprocal size.

254 citations


Journal ArticleDOI
TL;DR: The exact spectrum and thermodynamics of the S=1/2 Heisenberg chain with inverse-square exchange are explicitly obtained in closed form, and a description in terms of semionic spin- 1/2 «spinon» excitations is developed.
Abstract: The exact spectrum and thermodynamics of the S=1/2 Heisenberg chain with inverse-square exchange are explicitly obtained in closed form, and a description in terms of semionic spin-1/2 ``spinon'' excitations is developed. The unexpected degeneracies of the spectrum lead to a new representation of the k=1 SU(2) Wess-Zumino-Witten conformal field theory that exposes an infinite set of SU(2) symmetries of that model.

225 citations


Journal ArticleDOI
TL;DR: A phase diagram of the one-dimensional S=1/2 frustrated ferromagnetic Heisenberg model in a magnetic field is studied via a bosonization technique and the prediction is made of possible fourfold degeneracy of a ground state at H=0 for sufficiently strong second-neighbor coupling.
Abstract: A phase diagram of the one-dimensional S=1/2 frustrated ferromagnetic Heisenberg model in a magnetic field is studied via a bosonization technique. Besides the ferromagnetic phase, two different nematiclike phases with additional symmetry breaking of reflections about a bond or about a site are mapped out. The prediction is made of possible fourfold degeneracy of a ground state at H=0 for sufficiently strong second-neighbor coupling.

170 citations


Journal ArticleDOI
TL;DR: In this article, the anomalous g-values of pair and trimer Co2+ spins by EPR of Rb2Co0.3Mg0.7F4 at 220, 370, 762.2 and 693.6 GHz in pulsed high magnetic fields were found.
Abstract: We found new effect which changes g-values of pair and trimer Co2+ spins by EPR of Rb2Co0.3Mg0.7F4 at 220, 370, 762.2 and 693.6 GHz in pulsed high magnetic fields. The anomalous g-values come from mixing of 1LS and strong exchange interaction.

138 citations


Journal ArticleDOI
TL;DR: In this article, the random exchange potential at the interfaces between magnetic and nonmagnetic layers is proposed to be an origin of the giant magnetoresistance in metallic superlattices.
Abstract: The random exchange potential at the interfaces between magnetic and nonmagnetic layers is proposed to be an origin of the giant magnetoresistance in metallic superlattices. The material dependence of the potential is calculated for transition metal elements. An analysis using the Boltzmann equation shows that the theoretical results of the potential explain the giant magnetoresistance observed.

116 citations


Journal ArticleDOI
TL;DR: Calculs a potentiel integral de la structure electronique et des proprietes de l'etat fondamental du fer en utilisant les fonctionnelles de la densite locale de Langreth-Mehl-Hu, Perdew-Wang, et Becke.
Abstract: Full-potential calculations of the electronic structure and ground-state properties of iron using the Langreth-Mehl-Hu, Perdew-Wang, and Becke gradient-corrected local-density functionals are reported. As in earlier linear-muffin-tin-orbital calculations using the atomic-spheres approximation, a ferromagnetic bcc ground state is found, although there are differences in the energetics. The effect of the gradient corrections on the electronic structure is discussed in detail. It is found that there are significant changes in the exchange splittings that result from nonspherical terms in the potential, and these differ significantly depending on the choice of the gradient correction.

Journal ArticleDOI
TL;DR: Une analyse des liaisons fortes, des spectres d'absorption des rayons-x mous and du dichroisme magnetique circulaire (MCD) sur Ni aux seuils 2p→3d fournit des valeurs du parametre de l'interaction spin-orbite et de the decomposition d'echange.
Abstract: A tight-binding analysis of soft-x-ray-absorption and magnetic-circular-dichroism (MCD) spectra on Ni at the 2p\ensuremath{\rightarrow}3d thresholds yields values for the valence spin-orbit parameter and exchange splitting which are, respectively, larger and smaller than the ground-state band-structure values by a factor of \ensuremath{\sim}2. The discrepancies are attributed to core-hole correlation effects. A feature that appears 4 eV above the main white lines, but only in the MCD spectrum, is also attributed to correlation effects.

Journal ArticleDOI
TL;DR: The Gutzwiller wave function is shown to be the exact solution of a supersymmetric t-J-type model that realizes a Fermi-liquid state in one dimension with a discontinuity in the momentum distribution.
Abstract: The Gutzwiller wave function is shown to be the exact solution of a supersymmetric t-J-type model. The model realizes a Fermi-liquid state in one dimension with a discontinuity in the momentum distribution. Analytic results are obtained for spin and charge susceptibilities, and the specific-heat coefficient with the help of the Luttinger-liquid theory. In the high-density limit the model exhibits a Mott-Hubbard gap and reduces to an antiferromagnetic spin chain with long-range exchange solved by Haldane and Shastry.

Journal ArticleDOI
15 Aug 1991-EPL
TL;DR: In this paper, the exchange interaction of two Fe films across a Cr film as a function of the Cr thickness dCr was investigated by means of light scattering from spin waves and magneto-optical Kerr measurements.
Abstract: By means of light scattering from spin waves and magneto-optical Kerr measurements we investigated the exchange interaction of two Fe films across a Cr film as a function of the Cr thickness dCr. Using good-quality epitaxial samples with a special wedge geometry of the interspacer we observed up to four full periods of the long-range oscillations of the exchange, including its ferromagnetic parts. The decay of the oscillations does not follow the dCr-2-dependence predicted by classical two-dimensional RKKY-type theory. A fine structure in the first antiferromagnetic region is also observed.

Journal ArticleDOI
TL;DR: A large effective internal field in the Al film is found, which gives rise to extra Zeeman splitting in the superconducting quasiparticle density of states and which is attributed to the exchange interaction between the Eu ions and the Al conduction electrons.
Abstract: Using the technique of spin-polarized tunneling, we studied tunnel junctions with EuS/Al bilayer electrodes. We found a large effective internal field in the Al film, which gives rise to extra Zeeman splitting in the superconducting quasiparticle density of states and which is attributed to the exchange interaction between the Eu ions and the Al conduction electrons. This exchange field, acting only on the electron spins, is inversely proportional to the thickness of the Al, causes no observable orbital depairing in the Al, and leads to a first-order transition to the normal state.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the effect of the R-4f moments on the conduction band system of RFe 2 compounds and showed that the effect depends on the local exchange interaction between rare-earth and transition-metal moments.
Abstract: The combination of itinerant transition metal (M = Fe) and localized rare-earth (R = Gd-Y) magnetism in RFe 2 compounds has been investigated in self-consistent energy band calculations. The computed and measured total moments are in good agreement for all cases where single crystal data are available. We find, however, that there is a significant contribution to the moment from the R-5d partial moments coupled antiparallel to the Fe-3d moment which results from 3d–5d hybridization. The R-4f moments interact with the conduction band system solely by local exchange interactions, which are calculated ab initio from density functional theory. A sum rule for the total 3d + 5d moment is shown to be obeyed and the effective ferrimagnetic exchange interaction between rare-earth and transition-metal moments is discussed. Finally, the spin wave spectra of these materials are evaluated in terms of a model arising from these calculations.


Journal ArticleDOI
TL;DR: In this article, the anomalous spin-splitting phenomenon which exhibits the field-dependent spin splitting separation has been observed, assuming an antiferromagnetic exchange interaction between the electrons in the spin-up and spin-down states.

Book ChapterDOI
TL;DR: In this paper, the magnetic properties of ternary intermetallic rare-earth compounds are discussed, and the influence of these factors on magnetic properties are reviewed, as well as their influence on the magnetism of these compounds.
Abstract: Publisher Summary This chapter discusses the magnetic properties of ternary intermetallic rare-earth compounds. The values of the effective moments are deduced from the temperature dependence of the magnetic susceptibility. The disagreement between the experimental moments and the rare earth's free-ion moments is a result of a strong coupling of the conduction electrons with the localized moments. In the RKKY theory, the magnetic effective moment is given by the formula, described in the chapter. In the ternary rare-earth compounds discussed, the magnetic properties are determined by the rare-earth moments. The transition metal atoms T, except for Mn, do not carry magnetic moments. These materials have a metallic character and the interatomic distances between the rare-earth atoms are fairly large. The magnetic interaction between the highly localized 4f electrons is realized by their conduction electrons mediating in an exchange interaction, and by the effects of crystalline electric fields (CEF) acting on the 4f electrons. The chapter also reviews the influence of these factors on the magnetic properties. In metallic compounds of rare earths, exchange interactions between rare-earth moments are mediated by the spin polarization of conduction electrons. This leads to long-range exchange interactions with an oscillatory dependence of the interaction strength on the distance between the moments.

Journal ArticleDOI
TL;DR: From the results it is concluded that exchange interaction will in general contribute to an appreciable extent to the linewidth of core lines of magnetic systems.
Abstract: The energy distribution curves for 2p-core-level photoemission of Fe have been calculated based on a completely relativistic treatment of the core as well as the final states. In accordance with recent experiments, a pronounced dependence on the helicity of the exciting radiation has been found. All features of the experimental spectra could be explained in terms of ground-state properties calculated within the framework of local-spin-density-functional theory. From the results it is concluded that exchange interaction will in general contribute to an appreciable extent to the linewidth of core lines of magnetic systems.

Journal ArticleDOI
TL;DR: In this paper, the results of spin-polarized band-structure calculations on the ordered binary compounds of Co-Pr Comparison are made with experimental values for the magnetic moments.
Abstract: In this article the authors present the results of spin-polarized band-structure calculations on the ordered binary compounds of Co-Pr Comparison is made with experimental values for the magnetic moments The results of these calculations show a nonlocal magnetic moment behaviour in these systems Furthermore the authors find an almost constant number of holes in the Pt 5d band for the different compounds The nature of the magnetic interactions is investigated The coupling between the Co atoms can be described with the Heisenberg Hamiltonian and the exchange coupling parameters are evaluated With these exchange parameters the authors are able to calculate the Curie temperature of ordered and disordered Co-Pt alloys

Journal ArticleDOI
TL;DR: In this paper, the spin-1 Ising model with dipolar and quadrupolar exchange interactions was studied exactly and the phase diagrams were constructed based on recursion relations, which are exact in the infinite-dimensional case.
Abstract: The critical properties of the spin-1 Ising model on the Bethe lattice with dipolar and quadrupolar exchange interactions are studied exactly. This method is based on recursion relations, which are exact in the infinite-dimensional case, and as a result the phase diagrams are constructed. The λ-line ending in the tricritical point is defined exactly. It is shown that when the quadrupolar exchange interaction is large enough, the tricritical point disappears. The tricritical exponents are calculated exactly.

Journal ArticleDOI
TL;DR: In this paper, the mean field phase diagram of the spin-3 2 Ising model with a biquadratic exchange interaction (K) and a single ion anisotropy (D) was obtained by means of a variational method.
Abstract: The spin- 3 2 Ising model with a biquadratic exchange interaction (K) and a single ion anisotropy (D) is studied using two approaches. By means of a variational method we obtain the mean field phase diagram of the model. Besides a second order transition line occurring at high temperatures, the phase diagram exhibits two low temperature lines, which have not been reported previously. In the (T, D)-plane diagram a first order transition line separating the phases ( 3 2 , 3 2 ) and ( 1 2 , 1 2 ) occurs between the points (T = 0, D = −1.0) and (T ≈ 0.76, D ≈ −1.0). In the (T, K)-plane a line running in the non-zero temperature region from (T = 0, K = − 1 3 ) to (T = 0, K = −1.0) separates the region of equal sublattice magnetizations from that of unequal sublattice magnetizations. On the second approach, Monte Carlo simulations have been performed confirming the main qualitative predictions of the mean field calculations.

Journal ArticleDOI
TL;DR: In this article, the magnetic field effect (MFE) was monitored with optical methods: both absorption and emission spectroscopy, and discussed with the help of qualitative diagrams that provide an integrated picture of the combination of spin dynamics and molecular dynamics.
Abstract: Experimentally observed temperature-dependent shifts in magnetic-field-dependent reaction yield spectra of polymethylene-linked radical ion pairs are correlated with motional shifts in calculated spin-exchange spectra. The compounds investigated are pyrene-(CH{sub 2}){sub n}-N,N-dimethylaniline, n {le} 16, in the polar solvent acetonitrile. Radical ion pairs have been generated by photoinduced intramolecular electron transfer. The magnetic field effect (MFE) was monitored with optical methods: both absorption and emission spectroscopy. The MFE is explained and discussed with the help of qualitative diagrams that provide an integrated picture of the combination of spin dynamics and molecular dynamics. A through-space (solvent) exchange interaction is assumed in our discussions.


Journal ArticleDOI
TL;DR: In this paper, a simple model for spin-wave excitations and the low-temperature magnetization of ferromagnetic ultrathin films is presented, and the role of dipolar interactions is examined for a single monolayer and for thin films consisting of two or three atomic layers.
Abstract: A simple model is presented for spin-wave excitations and the low-temperature magnetization of ferromagnetic ultrathin films. The films are assumed to be quasi-two-dimensional arrays of fixed magnetic moments and both exchange and dipolar interactions are taken into account. Discrete and continuous models are used to examine the wave-vector dependence of the spin-wave frequency in the long-wavelength limit. This spin-wave theory can be used to calculate the temperature dependence of the saturation magnetization in the limit of small fluctuations. The role of dipolar interactions is examined for a single monolayer and for thin films consisting of two or three atomic layers.

Journal ArticleDOI
Kazuo Hida1
TL;DR: In this article, the properties of the spin-1/2 double chain Heisenberg antiferromagnet are studied by means of the numerical diagonalization and the projector Monte Carlo simulation.
Abstract: The properties of the spin-1/2 double chain Heisenberg antiferromagnet are studied by means of the numerical diagonalization and the projector Monte Carlo simulation. The model consists of the two spin 1/2 antiferromagnetic quantum Heisenberg chains coupled with each other via the ferromagnetic interchain coupling J ′ . It is shown that the first excited state has a gap for large enough J ′ . This gap continues to the Haldane gap in the limit J ′ →∞, where spins on the different chains form triplets on each site. On the other hand, the gap decreases rapidly between J ′ =1.0 and 0.6 and is undetectable for J ′ <0.6 within the present accuracy.

Journal ArticleDOI
TL;DR: Determination du diagramme de phases d'un systeme d'Ising mixte ferromagnetique, constitue de variables de spin 1/2 et de spin S, sur un reseau de Bethe de nombre de coordinence Z, avec des interactions d'echange entre plus proches voisins and des termes mono-ioniques.
Abstract: We obtain the phase diagram of a ferromagnetic mixed Ising system, consisting of spin-1/2 and spin-S variables, on a Bethe lattice of coordination number z, with nearest-neighbor exchange interactions and single-ion terms. The problem is formulated as a discrete nonlinear map. There is a tricritical point for S integer and z\ensuremath{\ge}5. In the infinite-coordination-number limit, we regain the results of an exact calculation for a Curie-Weiss version of the model.

Journal ArticleDOI
TL;DR: In this article, the critical behavior of a magnetic superlattice consisting of two different ferromagnets is examined in a simple cubic Ising model with nearest-neighbor coupling and it is found that there exists a critical value of the interface exchange coupling above which the interface magnetism appears.

Journal ArticleDOI
TL;DR: Cette theorie microscopique inclut des interactions dipolaires and d'echange entre les spins, l'anisotropie de surface du caractere monosite quadratique and quartique dans les composantes des spins.
Abstract: We present theoretical studies of the classical ground-state spin configuration and spin waves, in very thin ferromagnetic films, with thickness that ranges from a monolayer to a few tens of layers. The analyses are based on a microscopic model that includes dipolar and exchange interactions between the spins, surface (or interface) anisotropy of single-site character quadratic and quartic in the spin components, along with an external magnetic field applied at an arbitrary direction with respect to the film normal. Issues explored include the nature of spin canting induced by surface anisotropy in ultrathin (few-atomic-layer) films, and in films with thicknesses of up to 100 layers. Also, we explore the nature of spin waves in ultrathin films, in the presence of spin canting, and in thicker films with attention to the interplay between dipolar and exchange contributions to the excitation energy. Most particularly, in the thicker films, we examine the transition from the dipole-dominated Damon-Eshbach waves to the exchange-dominated surface spin waves that emerge from the Heisenberg model.