Kazuko Motizuki

First principles electronic band calculation of (Zn, Cr)Te, (Zn, Cr)Se and (Zn, Cr)S

Electronic band structure of magnetic semiconductors based on II–VI compounds such as Zn1−xCrxX (X=Te, Se, S; x=1, 0.5, 0.25) are calculated for non-magnetic (NM), ferromagnetic (F) and antiferromagnetic (AF) states by using the full-potential linearized augmented-plane-wave method. In the F state, the half-metallic behavior is found in hypothetical zinc-blende type CrTe and CrSe and also in Zn0.5Cr0.5Te and Zn0.75Cr0.25Te. CrS shows metallic behavior. The magnetic polarization antiparallel to the Cr moment is induced at the neighboring Te, Se and S sites, respectively, and a magnitude of the induced moment decreases in the order of CrTe, CrSe and CrS. By calculating the total energy of each state, we have found that in all compounds, the F state is stable compared with the NM state. Furthermore, in the case of x=1, by comparing the total energy of the F state with that of the AF state described by Q=(0,0,2π/a), we have found that the F state is most stable in CrTe and CrSe and the AF state is stable in CrS. The AF band calculations for x=0.5 and 0.25 remain as a future problem.

Effect of intercalation on structural instability and superconductivity of layered 2H-type NbSe2 and NbS2

Abstract Effects of intercalation on the lattice instability and the superconductivity of NbSe2 and NbS2 are studied in the framework of the rigid band approximation. In the case of doping acceptor-type intercalants into NbSe2, the point of lattice instability in q-space is moved to q = Γ M from q = 2 3 ΓM . Further, the frequency renormalization is enhanced and the CDW transition temperature is expected to increase. In the case of doping donor-type intercalants, on the other hand, the frequency renormalization is weakened and the lattice instability is suppressed. The same tendency is found also in NbS2. The effect of intercalation on the superconducting transition temperature Tc of NbS2 is investigated by calculating the functional derivative of Tc with respect to the spectral function. The donor-type intercalant lowers Tc as observed in the case of alkali-metal doping. On the other hand, the acceptor-type intercalant raises Tc as long as the lattice instability does not take place.

Electronic band structure and magnetic and optical properties of Fe7Se8 and Co7Se8

Abstract First-principles electronic band structure calculations are performed for cation-deficient NiAs-type transition-metal compounds Fe7Se8 and Co7Se8 by using the LAPW method. The magnetic moment calculated for ferrimagnetic Fe7Se8 agrees well with the observed value. Photoemission and optical conductivity spectra are calculated for both compounds and the results are compared with the observations.

Electronic band structure and photoemission spectra of Fe7S8

First-principles electronic band structure calculations are performed for a cation-deficient NiAs-type ferrimagnet Fe7S8 (pyrrhotite) by using the linearized augmented-plane-wave (LAPW) method based on the local density approximation for the exchange-correlation potential. The magnetic moment, the magnetic hyperfine field, the isomer shift, and the Fe 3s core-level spin-splitting are evaluated for each iron-site. Valence-band ultraviolet photoemission and inverse photoemission spectra are calculated for the ferrimagnetic state of Fe7S8 and the results are compared with recent observations.

Pressure effect on electronic band structures of NiAs-type CrTe, CrSe and CrS

The electronic band calculation of NiAs-type Cr-charcogenides is performed for non-magnetic, ferromagnetic and antiferromagnetic states by using the FLAPW method, and studied the pressure effect on the electronic structure. From the total energy calculated as a function of lattice parameter, pressure induced ferromagnetic → antiferromagnetic transition is expected in CrTe at about 40 GPa. In CrSe and CrS an antiferromagnetic state is most stable.

Electronic band structure of Li2CuO2

Abstract Electronic band calculations for non-magnetic and antiferromagnetic states of Li 2 CuO 2 are performed by using the FLAPW method. Cu-3d states are strongly hybridized with O-2p states. For the non-magnetic state, a narrow antibonding band is separated from broad due5f8p mixing bands and half filled with an electron. For the antiferromagnetic state, the calculated magnetic moment is extended on the CuO 2 chain.

Electronic structure and magnetism of diluted magnetic semiconductor (Zn, Cr)Te

Abstract Electronic band structures of magnetic semiconductors based on zinc-blende type II–VI compounds such as Zn1−xCrxTe (x=1, 0.5 and 0.25) are calculated for non-magnetic (NM), ferromagnetic (F) and antiferromagnetic (AF) states, by using the full-potential linearized augmented-plane-wave (FLAPW) method. In the F state, the half-metallic behavior is found and the magnetic polarization antiparallel to the Cr moment is induced at the neighboring Te-site. By calculating the total energy of each state, we have found that the F state is always stable compared with the NM state. In the case of the hypothetical zinc-blende type CrTe, the F state has been found to be stable compared with the AF state described by Q =(0, 0, 2π/ a) .

First-principles study on lattice dynamics and electron-phonon interaction in an oxide spinel LiTi2O4

Abstract Frozen-phonon method with use of the full-potential linearized augmented-plane-wave band calculations has been applied to the all-symmetric A1g phonon mode of the superconducting spinel LiTi2O4 for which there are no available experimental data of phonon frequencies. The phonon frequency of the A1g mode and the maximum value of its relative phonon line width due to the electron-phonon interaction have been evaluated to be 80 meV and 0.064, respectively. These results show good correspondence to those obtained semi-empirically by our previous work.

Electronic state and g-factor of Er3+ ion doped in InP

The electronic state of Er3+ ion doped in InP is investigated by calculating the crystalline electric field at Er ion that substitutes an In ion in InP. The energy level of the 16-fold degenerate J states of Er3+ ion is split into two doublets and three quartets. For the obtained ground doublet, g-factor is evaluated. Results are discussed in connection with observations.

Electronic and magnetic properties of Li2CuO2

Abstract We have performed an electronic band calculation for non-magnetic (NM) and antiferromagnetic (AF) states of Cu–O edge-sharing compound Li2CuO2 by using the FLAPW method with local spin-density approximation (LSDA) and LSDA+U approximation. In the NM-state a narrow antibonding band crosses the Fermi level and consists of strongly hybridized Cu 3 d yz and O 2 p y states. The Fermi surface of the NM state reveals a nesting effect which plays an important role in causing the observed antiferromagnetic ordering. In the AF state the narrow antibonding band in the NM state is split and a small bandgap appears at the Fermi level. LSDA+U calculation leads to a much wider bandgap than the LSDA calculation.