Electronic structure and magneto-optical Kerr effect in UCuAs₂

The optical and magneto-optical (MO) spectra of the ternary compound UCuAs₂ are investigated theoretically from first principles, using the fully relativistic Dirac linear-muffin-tin-orbital band structure method. The electronic structure is obtained with the local spin-density approximation (LSDA), as well as with the so-called LSDA+U approach. Better agreement between the theoretically calculated and the experimentally measured MO Kerr spectra is found with the LSDA+U approximation. The origin of the Kerr rotation in the compound is examined

Statistical coarse-graining as an approach to multiscale problems in magnetism

Multiscale phenomena which include several processes occuring simultaneously at different length scales and exchanging energy with each other, are widespread in magnetism. These phenomena often govern the magnetization reversal dynamics, and their correct modeling is important. In the present paper, we propose an approach to multiscale modeling of magnets, applying the ideas of coarse graining. We have analyzed the choice of the weighting function used in coarse graining, and propose an optimal form for this function. Simple tests provide evidence that this approach may be useful for modeling of realistic magnetic systems.Comment: 5 RevTeX pages, 2 figure

Electronic structure and x-ray magnetic circular dichroism in uranium monochalcogenides

The electronic structure and x-ray magnetic circular dichroism (XMCD) spectra of US, USe, and UTe are investigated theoretically from first principles, using the fully relativistic Dirac LMTO band structure method. The electronic structure is obtained with the local spin-density approximation (LSDA), as well as with a generalization of the LSDA+U method which takes into account that in the presence of spin–orbit coupling the occupation matrix of localized electrons becomes non-diagonal in spin indexes. The origin of the XMCD spectra in the compounds is examined

Electronic structure and magneto-optical Kerr effect in the compound UCuP₂

The optical and magneto-optical (MO) spectra of the fernary compound UCuP₂ are investigated from first principles, using the fully relativistic Dirac linear-muffin-tin-orbital band structure method and density-functional theory in the local spin-density approximation. Within a band-like description of the 5f electrons, good agreement with the measured MO spectra is obtained. The origin of the Kerr rotation in the compound is examined

Destruction of the Kondo effect by a local measurement

We show that the local spin measurement which decoheres the localized spin in a Kondo system, suppresses the Abrikosov-Suhl resonance and destroys the Kondo effect. This happens due to elimination of the entanglement between the localized spin and the conduction electrons, and differs essentially from smearing of the resonance by dissipation. Considering decoherence by a spin bath, we predict that the Kondo effect disappears when the Kondo temperature becomes smaller than the coupling with a bath. This effect can be detected in experiments on ``quantum corrals'' or quantum dots doped by impurities with internal degrees of freedom.Comment: REVTeX4, 1 figure (EPS

Metallic ferromagnetism without exchange splitting

In the band theory of ferromagnetism there is a relative shift in the position of majority and minority spin bands due to the self-consistent field due to opposite spin electrons. In the simplest realization, the Stoner model, the majority and minority spin bands are rigidly shifted with respect to each other. Here we consider models at the opposite extreme, where there is no overall shift of the energy bands. Instead, upon spin polarization one of the bands broadens relative to the other. Ferromagnetism is driven by the resulting gain in kinetic energy. A signature of this class of mechanisms is that a transfer of spectral weight in optical absorption from high to low frequencies occurs upon spin polarization. We show that such models arise from generalized tight binding models that include off-diagonal matrix elements of the Coulomb interaction. For certain parameter ranges it is also found that reentrant ferromagnetism occurs. We examine properties of these models at zero and finite temperatures, and discuss their possible relevance to real materials

Electronic structure of a Mn12 molecular magnet: Theory and experiment

金沢大学大学院自然科学研究科物質情報解析We used site-selective and element-specific resonant inelastic x-ray scattering (RIXS) to study the electronic structure and the electron interaction effects in the molecular magnet [Mn12 O12 (C H3 COO)16 (H2 O)4] 2C H3 COOH 4 H2 O, and compared the experimental data with the results of local spin density approximation +U electron structure calculations which include the on-site Coulomb interactions. We found a good agreement between theory and experiment for the Coulomb repulsion parameter U=4 eV. In particular, the p-d band separation of 1.8 eV has been found from the RIXS spectra, which is in accordance with the calculations. Similarly, the positions of the peaks in the XPS spectra agree with the calculated densities of p and d states. Using the results of the electronic structure calculations, we determined the intramolecular exchange parameters, and used them for diagonalization of the Mn12 spin Hamiltonian. The calculated exchanges gave the correct ground state with the total spin S=10. © 2007 The American Physical Society

THE ELECTRONIC STRUCTURE OF RARE-EARTHS.Band structures of rare earth metals

Des mesures récentes de propriétés magnétiques et optiques des métaux de terres rares ont fourni une information très détaillée concernant la structure électronique de ces métaux. Pour en rendre compte, il apparaît qu'il faut améliorer les modèles simples qu'on a employés jusqu'à présent pour interpréter les données expérimentales. Dans une théorie plus détaillée on doit incorporer un traitement relativiste de la polarization des spins électroniques et aussi tenir compte de la localisation des électrons 4f au voisinage des atomes. On est guidé dans ces calculs par les résultats de mesures récentes des propriétés des métaux de terres rares et par des calculs de champ self-consistent des propriétés de métaux qui ne sont pas magnétiques mais possèdent une structure électronique semblable. Dans cet article je présente une revue critique des calculs de la structure électronique des métaux de terres rares et en particulier des calculs détaillés pour gadolinium.Recent magnetic, optical and neutron scattering experiments made possible by the availability of high purity samples are providing increasingly detailed information about the electronic structure of the rare earth metals. The first calculations for the paramagnetic state of these fascinating metals have long served as a valuable heuristic model for understanding many earlier experimental results. It is expected that more accurate calculations for the magnetic ground state will be equally valuable in fostering the traditionally fruitful interaction between theory and experiment. Such calculations present a formidable challenge since they require a relativistic approach to spin polarization and a suitable treatment of the highly localized 4f-shell. The calculations can be guided by comparison with precise experimental results and by self-consistent calculations for non-magnetic metals with similar electronic structures. In this paper we review the present status of band structure calculations for the rare earth metals, and give details of a self-consistent, relativistic, ferromagnetic calculation for gadolinium

THEORETICAL ASPECTS OF NEUTRON MAGNETIC FORM FACTORS

On présente une revue des calculs de densités magnétiques dans les solides. Si le modèle atomique reste utile comme première approximation, il est nécessaire de faire appel aux méthodes plus élaborées de calculs de structure de bandes pour obtenir d'une manière ab initio les densités de spin dans les solides. On discute les calculs des contributions orbitales induites par un champ externe ou dues au couplage spin-orbite.The calculation of magnetization densities in solids is reviewed. The atomic model is still a useful first approximation while the more involved band structure approach is required for first principle calculations of solid state spin densities. The calculation of orbital contributions, either induced by an applied field or caused by spin-orbit coupling, is discussed

Multiplet fine structure in the photoemission of the gadolinium and terbium 5p levels

Fine structure is observed in the photoemission of the gadolinium and terbium 5p levels. The 5p levels are split into multiplets due to spin-orbit splitting and to Coulomb and exchange interactions with the f shell. The calculated theoretical spectra are in good agreement with the experimental results