Tatsuya Nagao

1/S-expansion study of spin waves in a two-dimensional Heisenberg antiferromagnet

We study the effects of quantum fluctuations on excitation spectra in the two-dimensional Heisenberg antiferromagnet by means of the 1/S expansion. We calculate the spin-wave dispersion and the transverse dynamical structure factor up to the second order of 1/S in comparison with inelastic neutron scattering experiments. The spin-wave energy at momentum

Radial integrals for the magnetic form factor of 5d transition elements.

(\pi,0)

Resonant X-Ray Scattering from the Quadrupolar Ordering Phase of CeB6

is found to be about 2% smaller than that at

Resonant x-ray scattering spectra from multipole ordering: Np M 4 , 5 edges in Np O 2

(\pi/2,\pi/2)

Resonant X-ray scattering from CeB6

due to the second-order correction. In addition, we study the dimensional crossover from two dimensions to one dimension by weakening exchange couplings in one direction. It is found that the second-order correction becomes large with approaching the quasi-one dimensional situation and makes the spin-wave energy approach to the des Cloizeaux-Pearson boundary for

Analysis of optical magnetoelectric effect in GaFeO 3

S=1/2

Lattice Distortion and Resonant X-Ray Scattering in DyB2C2

. The transverse dynamical structure factor is also calculated up to the second order of 1/S. It is shown that the intensity of spin-wave peak is strongly reduced while the intensity of three-spin-wave continuum becomes large and exceeds that of the spin-wave peak in the quasi-one dimensional situation.

A Phenomenological Model for the Critical Temperature of Layered Superconductors

The radial integrals, j(L), where L = 0, 2, 4, for several electronic configurations in the 5d electrons of transition metal atoms and ions are calculated using radial wavefunctions from the pseudo-relativistic Hartree-Fock method in the Cowan program. The resultant values are fitted to Gaussian analytical expressions with four exponential terms, and the fitted coefficients are tabulated. This table can be used to interpret the magnetic form factor measurements for 5d transition metals.

Spectral analysis of resonant x-ray scattering in CeB 6 under an external magnetic field

We theoretically investigate the origin of the resonant X-ray scattering (RXS) signal near the Ce L III absorption edge in the quadrupolar ordering phase of CeB 6 , considering the intersite interaction between the Γ 8 states in the initial state. The anisotropic charge distribution of the 4f states modulates the 5d states through the intra-atomic Coulomb interaction and thereby generates a large RXS superlattice intensity. The temperature and magnetic field dependence indicates that the induced dipolar and octupolar orders have little influence on the RXS spectra, in good agreement with the recent experimental results.

Interference between Thomson Scattering and Resonant Scattering in X-Ray Diffraction from CeB6

We study resonant x-ray scattering (RXS) at Np M_{4,5} edges in the triple-\textbf{k} multipole ordering phase in NpO_{2}, on the basis of a localized electron model. We derive an expression for RXS amplitudes to characterize the spectra under the assumption that a rotational invariance is preserved in the intermediate state of scattering process. This assumption is justified by the fact that energies of the crystal electric field and the intersite interaction is smaller than the energy of multiplet structures. This expression is found useful to calculate energy profiles with taking account of the intra-Coulomb and spin-orbit interactions. Assuming the \Gamma_{8}-quartet ground state, we construct the triple-\textbf{k} ground state, and analyze the RXS spectra. The energy profiles are calculated in good agreement with the experiment, providing a sound basis to previous phenomenological analyses.