Takeo Jo

Effect of Coulomb interaction on the X-ray magnetic circular dichroism spin sum rule in 3d transition elements

A deviation from the X-ray magnetic circular dichroism (MCD) spin sum rule, which is derived assuming well separated core spin-orbit multiplets in the final state of X-ray absorption, is calculated for the L 2,3 edge in the magnetized Ni, Co, Fe and Mn ions on the basis of an atomic model including the full multiplet and the crystal field with O h symmetry. Due to the Coulomb interaction between electrons, which mixes the so-called L 3 and L 2 regions with each other, it is found that the deviation can be ∼10 percent for the former three ions, while for Mn 2+ it amounts to more than 30 percent. A list of the deviations for various ionic states for the above elements is presented, which may serve as a correction factor in the estimation of expectation values of magnetic quantities from MCD data.

Electronic Structure of Ni-Mn and Ni-Fe Alloys

The electronic structures of ferromagnetic Ni-Mn and Ni-Fe alloys are investigated theoretically. The Hartree-Fock calculation combined with the coherent potential approximation is shown to give two magnetic states for Mn and Fe atoms in Ni-Mn and Ni-Fe alloys, respectively. By introducing the ternary alloy picture in which Mn(Fe) atoms having antiparallel moments to the bulk magnetization are distinguished from Mn(Fe) atoms having parallel moments for a given Ni-Mn(Ni-Fe) alloy, the possibility of the coexistence of the two magnetic states is shown by an energy consideration. On the basis of the results obtained by this calculation, various magnetic properties are discussed.

Magnetic Circular Dichroism in Core X-Ray Absorption Spectra of Rare-Earths

We present a calculation of magnetic circular dichroism in 3 d and 4 d core X-ray absorption spectra of rare earth systems assuming that a trivalent rare earth ion is placed in an infinitesimal uniform magnetic field. The calculation covers all rare earth elements between Ce and Tm. Features of the dichroism are explained by elementary considerations of transition matrix of a polarized light, spin-orbit coupling of a core hole, and exchange interaction between a core hole and a 4 f electron.

Orbital ordering in La0.5Sr1.5MnO4 studied by soft x-ray linear dichroism

We found that the conventional model of orbital-ordering of 3x(2)-r(2)/3y(2)-r(2) type in the e(g) states of La0.5Sr1.5MnO4 is incompatible with measurements of linear dichroism in the Mn 2p-edge x-ray absorption, whereas these e(g) states exhibit predominantly cross-type orbital ordering of x(2)-z(2)/y(2)-z(2). LDA+U band-structure calculations reveal that such a cross-type orbital-ordering results from a combined effect of antiferromagnetic structure, Jahn-Teller distortion, and on-site Coulomb interactions.

Theory of 3d Core Level Spectra of CeO2 and Metallic Ce Compounds

Core level spectra for a mixed valent insulator CeO 2 and typical mixed valent metallic Ce compounds are discussed on the basis of the filled band Andersom model, which is found to give sufficiently correct core spectra even for a metallic system when the spin and orbital degeneracy of 4 f orbitals is large. A remarkable difference in the 3 d core photoemission spectrum and an apparent similarity in the 3 d -core photoabsorption spectrum between CeO 2 and metallic Ce compounds are consistently explained and an expected difference in the resonant photoemission spectrum near the Ce 3 d threshold between the two systems is discussed. The 4 f 3 configuration of Ce atom is taken into account in the calculation and its effect on core spectra is discussed. The analysis of core spectra neglecting the 4 f 3 configuration can be shown to underestimate the Coulomb interaction between 4 f electrons. So far proposed assignment for peak of core spectra is critically examined.

Effect of Coulomb Interaction on the X-Ray Magnetic Circular Dichroism Spin Sum Rule in Rare Earths

A deviation from the spin sum rule, which relates the integrated intensity of the X-ray magnetic circular dichroism (MCD) signal to the expectation value of the spin operator S z ( ), is numerically calculated in the case of the 3 d →4 f absorption for rare earths from the trivalent Ce to Tm. The calculation on the basis of an atomic model including the full multiplet shows that the deviation increases from ∼60 % for Ce with increasing 4 f electron number, reaches at ∼230 % for Sm and drops to less than ∼10 % for Gd and heavier rare earths. An interplay of the 3 d -4 f exchange interaction, the 3 d core spin-orbit interaction and the 4 f electron configuration in the initial ground state is shown to cause the chemical trend of the deviation from the sum rule.

Many Body Effect in Inner Shell Photoemission and Photoabsorption Spectra of La Compounds

Theoretical analysis is made for spectra of the 3 d core photoemission (3 d -XPS) and 2 p core photoabsorption ( L 3 -XAS) in insulating La compounds La 2 O 3 , LaF 3 and LaCl 3 by using the single-site Anderson model. In order to give a consistent interpretation for 3 d -XPS and L 3 -XAS, it is essentially important to take into account, in the final state of L 3 -XAS, the Coulomb interaction U f d (between 4 f and 5 d electrons) and - U d c (between a 5 d electron and a core hole) in addition to - U f c (between a 4 f electron and a core hole). A similar analysis is also presented for the intermetallic cornpound LaPd 3 .

Electronic State of Mn Impurity in Ferromagnetic Ni-Co Alloys : Localized Moment Behavior

The existence of two magnetic states and the effect of the local atomic environment on these states for atoms in random ferromagnetic alloys are investigated in the Hartree-Fock approximation. Electronic states of a single impurity Mn atom in Ni-Co alloys are calculated with varying the numbers of Ni and Co atoms on the nearest neighbor sites and the alloy concentration. From an energy consideration, it is concluded that the magnetic moment of the Mn is parallel to the bulk magnetization in Ni-rich environment, while it is antiparallel in Co-rich ones.

Lattice Distortion and Multiple Spin Density Wave State in γMn Alloys

The relation between tetragonal lattice distortion observed in Mn-rich γMn alloys such as MnNi, MnFe and MnCu and their magnetic structures is investigated on the basis of the Landau expansion of free energy. By taking into account a coupling between lattice distortions and three magnetic order parameters specifying the first-kind antiferromagnetic ordering on the fcc lattice, possible phase diagrams in the temperature-composition plane are discussed. Observed various types of phase diagram for lattice distortion including the orthorhombic phase in γMnNi alloys are shown to be well explained and the type of multiple spin density wave state for each phase is predicted.

Configuration Interaction in Ni Metal and Ni Alloys and High-Energy Spectroscopy

We discuss the electronic state of Ni atoms in Ni metal and of Ni impurity in Cu and Au metals from the viewpoint of 3 d configuration interaction (CI) using the Anderson impurity model including atomic multiplets. On the basis of the discussion, we give an interpretation for the Ni 2 p -core X-ray photoemission spectrum (2 p XPS) in Ni metal and Ni impurity systems and 3 d photoemission spectra in Ni metal. The interpretation is, furthermore, shown to be consistent with the previous one for the 2 p →3 d circularly polarized X-ray absorption in ferromagnetic Ni using the CI approach.