55 research outputs found
Band-theoretical prediction of magnetic anisotropy in uranium monochalcogenides
Magnetic anisotropy of uranium monochalcogenides, US, USe and UTe, is studied
by means of fully-relativistic spin-polarized band structure calculations
within the local spin-density approximation. It is found that the size of the
magnetic anisotropy is fairly large (about 10 meV/unit formula), which is
comparable with experiment. This strong anisotropy is discussed in view of a
pseudo-gap formation, of which crucial ingredients are the exchange splitting
of U 5f states and their hybridization with chalcogen p states (f-p
hybridization). An anomalous trend in the anisotropy is found in the series
(US>>USe<UTe) and interpreted in terms of competition between localization of
the U 5f states and the f-p hybridization. It is the spin-orbit interaction on
the chalcogen p states that plays an essential role in enlarging the strength
of the f-p hybridization in UTe, leading to an anomalous systematic trend in
the magnetic anisotropy.Comment: 4 pages, 5 figure
Orbital ordering and enhanced magnetic frustration of strained BiMnO3 thin films
Epitaxial thin films of multiferroic perovskite BiMnO3 were synthesized on
SrTiO3 substrates, and orbital ordering and magnetic properties of the thin
films were investigated. The ordering of the Mn^{3+} e_g orbitals at a wave
vector (1/4 1/4 1/4) was detected by Mn K-edge resonant x-ray scattering. This
peculiar orbital order inherently contains magnetic frustration. While bulk
BiMnO3 is known to exhibit simple ferromagnetism, the frustration enhanced by
in-plane compressive strains in the films brings about cluster-glass-like
properties.Comment: 8 pages, 4 figures, accepted to Europhysics Letter
Electronic structure properties and BCS superconductivity in beta-pyrochlore oxides: KOs_2O_6
We report a first-principles density-functional calculation of the electronic
structure and properties of the recently discovered superconducting
beta-pyrochlore oxide KOs_2O_6. We find that the electronic structure near the
Fermi energy E_F is dominated by strongly hybridized Os-5d and O-2p states. A
van Hove singularity very close to E_F leads to a relatively large density of
states at E_F, and the Fermi surface exhibits strong nesting along several
directions. These features could provide the scattering processes leading to
the observed anomalous temperature dependence of the resistivity and to the
rather large specific heat mass enhancement we obtain from the calculated
density of states and the observed specific heat coefficient. An estimate of
T_c within the framework of the BCS theory of superconductivity taking into
account the possible effects of spin fluctuations arising from nesting yields
the experimental value.Comment: 5 pages, 4 figures; submitted for publicatio
Unquenched large orbital magnetic moment in NiO
Magnetic properties of NiO are investigated by incorporating the spin-orbit
interaction in the LSDA+U scheme. It is found that the large part of orbital
moment remains unquenched in NiO. The orbital moment contributes about mu_L =
0.29 mu_B to the total magnetic moment of M = 1.93 mu_B, as leads to the
orbital-to-spin angular momentum ratio of L/S = 0.36. The theoretical values
are in good agreement with recent magnetic X-ray scattering measurements.Comment: 4 pages, 2 figure
Observation of orbital angular momentum in the chiral magnet CrNb3S6 by soft x-ray magnetic circular dichroism
The chiral magnet CrNb3S6 with its solitonic objects has novel magnetic and transport properties, in which the spin-orbit coupling (SOC) plays a central role. Aiming to address the possible existence of orbital moments driven by SOC, we perform soft x-ray magnetic circular dichroism spectroscopy at the Cr L2,3 edges with in-plane magnetization. The dichroic signals provide direct experimental evidence that the Cr orbital magnetic moment is not quenched and is coupled antiparallel to the spin counterpart. Application of the orbital sum rule reveals that the magnitude of the Cr orbital moment is about 1% of the total magnetization. These findings are consistent with the first-principles electronic structure calculations that utilize the Cr 2p core radial function to define the Cr local 3d quantities. The distinct roles of the atomic SOC among the Cr 3d and Nb 4d states are discussed
Resonant X-ray Scattering in Manganites - Study of Orbital Degree of Freedom -
Orbital degree of freedom of electrons and its interplay with spin, charge
and lattice degrees of freedom are one of the central issues in colossal
magnetoresistive manganites. The orbital degree of freedom has until recently
remained hidden, since it does not couple directly to most of experimental
probes. Development of synchrotron light sources has changed the situation; by
the resonant x-ray scattering (RXS) technique the orbital ordering has
successfully been observed . In this article, we review progress in the recent
studies of RXS in manganites. We start with a detailed review of the RXS
experiments applied to the orbital ordered manganites and other correlated
electron systems. We derive the scattering cross section of RXS where the
tensor character of the atomic scattering factor (ASF) with respect to the
x-ray polarization is stressed. Microscopic mechanisms of the anisotropic
tensor character of ASF is introduced and numerical results of ASF and the
scattering intensity are presented. The azimuthal angle scan is a unique
experimental method to identify RXS from the orbital degree of freedom. A
theory of the azimuthal angle and polarization dependence of the RXS intensity
is presented. The theoretical results show good agreement with the experiments
in manganites. Apart from the microscopic description of ASF, a theoretical
framework of RXS to relate directly to the 3d orbital is presented. The
scattering cross section is represented by the correlation function of the
pseudo-spin operator for the orbital degree of freedom. A theory is extended to
the resonant inelastic x-ray scattering and methods to observe excitations of
the orbital degree of freedom are proposed.Comment: 47 pages, 24 figures, submitted to Rep. Prog. Phy
Nonquasiparticle states in half-metallic ferromagnets
Anomalous magnetic and electronic properties of the half-metallic
ferromagnets (HMF) have been discussed. The general conception of the HMF
electronic structure which take into account the most important correlation
effects from electron-magnon interactions, in particular, the spin-polaron
effects, is presented. Special attention is paid to the so called
non-quasiparticle (NQP) or incoherent states which are present in the gap near
the Fermi level and can give considerable contributions to thermodynamic and
transport properties. Prospects of experimental observation of the NQP states
in core-level spectroscopy is discussed. Special features of transport
properties of the HMF which are connected with the absence of one-magnon
spin-flip scattering processes are investigated. The temperature and magnetic
field dependences of resistivity in various regimes are calculated. It is shown
that the NQP states can give a dominate contribution to the temperature
dependence of the impurity-induced resistivity and in the tunnel junction
conductivity. First principle calculations of the NQP-states for the prototype
half-metallic material NiMnSb within the local-density approximation plus
dynamical mean field theory (LDA+DMFT) are presented.Comment: 27 pages, 9 figures, Proceedings of Berlin/Wandlitz workshop 2004;
Local-Moment Ferromagnets. Unique Properties for Moder Applications, ed. M.
Donath, W.Nolting, Springer, Berlin, 200
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