Muon spin relaxation studies of magnetic-field-induced effects in high-Tc superconductors

Muon spin relaxation measurements in high transverse magnetic fields [FORMULA: SEE TEXT] revealed strong field-induced quasistatic magnetism in the underdoped and Eu-doped (La,Sr)2CuO4 and La1.875Ba0.125CuO4, existing well above Tc and TN. The susceptibility counterpart of Cu spin polarization, derived from the muon spin relaxation rate, exhibits a divergent behavior towards T approximately 25 K. No field-induced magnetism was detected in overdoped La1.81Sr0.19CuO4, optimally doped Bi2212, and Zn-doped YBa2Cu3O7.     

Diffuse scattering and phason fluctuations in the Zn-Mg-Sc icosahedral quasicrystal and its Zn-Sc periodic approximant

We report on the absolute scale measurement of the x-ray diffuse scattering in the ZnMgSc icosahedral quasicrystal and its periodic approximant. Whereas the diffuse scattering in the approximant is purely accounted for by thermal diffuse scattering, an additional signal is observed in the quasicrystal. It is related to phason fluctuations as indicated by its Q(2)(per) dependence. Moreover, when compared to previous measurements carried out on the i-AlPdMn phase, we find that the amount of diffuse scattering is smaller in the i-ZnMgSc phase, in agreement with larger phason elastic constants in this phase. This is confirmed by the observation of a large number of weak Bragg peaks having a high Q(per) reciprocal space component.     

X-ray directional dichroism of a polar ferrimagnet

In a polar ferrimagnet GaFeO3, we have found a novel magneto-optical effect, termed x-ray nonreciprocal directional dichroism (XNDD), that the x-ray absorption at around the K edge of an Fe ion depends on whether the x-ray propagation vector is parallel or antiparallel to the outer product of the magnetization and electric-polarization vectors. The XNDD spectroscopy as demonstrated here can be a useful tool to probe the local magnetism in noncentrosymmetric systems such as magnetic interfaces and nanostructures.     

Magnetization-induced second harmonic generation in a polar ferromagnet

Second harmonic generation (SHG) induced by spontaneous magnetization has been investigated for a polar ferromagnetic crystal of GaFeO3. The Kerr rotation of the second harmonic light becomes gigantic with decreasing temperature below the magnetic transition temperature (approximately =205 K), e.g., as large as 73 degrees at 100 K. The magnetic domains can be visualized by using that large nonlinear Kerr rotation. The spectrum of the magnetization-induced SHG as measured indicates the two-photon resonant electronic process on a Fe3+ ion in the crystal.     

Change of electronic structure in Ca2RuO4 induced by orbital ordering

Optical conductivity spectra sigma(omega) were used to investigate the effect of orbital ordering on the electronic structure of Ca2RuO4. Our LDA+U calculation predicts Ru 4d(xy) ferro-orbital ordering at the ground state, and well explains the present sigma(omega) as well as the reported O 1s x-ray absorption spectra. Variation of temperature (T) causes a large change of spectral weight over several eV as well as collapse of a charge gap accompanied by elongation of the c-axis Ru-O bond length. These results clearly indicate that the d(xy) orbital ordering plays a crucial role in the metal-insulator transition and the T-dependent electronic structure on a large energy scale.     

Photochromic radical compounds based on a naphthopyran system

[reaction: see text] Naphthopyran derivatives with aminoxyl substituents (4a,b) gave the corresponding open-formed isomers (5a,b) by irradiation, which could be changed back to the starting closed-formed naphthopyrans by the treatment with SiO(2) as a catalyst. The tuning of intermolecular magnetic interactions between the isomer couples was found to be possible in these reversible systems.     

Reduction of ion thermal diffusivity associated with the transition of the radial electric field in neutral-beam-heated plasmas in the large helical device

Recent large helical device experiments revealed that the transition from ion root to electron root occurred for the first time in neutral-beam-heated discharges, where no nonthermal electrons exist. The measured values of the radial electric field were found to be in qualitative agreement with those estimated by neoclassical theory. A clear reduction of ion thermal diffusivity was observed after the mode transition from ion root to electron root as predicted by neoclassical theory when the neoclassical ion loss is more dominant than the anomalous ion loss.     

Observation of the "self-healing" of an error field island in the large helical device

It was observed that the vacuum magnetic island produced by an external error magnetic field in the large helical device shrank in the presence of plasma. This was evidenced by the disappearance of flat regions in the electron temperature profile obtained by Thomson scattering. This island behavior depended on the magnetic configuration in which the plasmas were produced.     

Dispersion resulting from phase and amplitude errors in arrayed-waveguide grating multiplexers-demultiplexers

We report dispersion resulting from phase and amplitude errors in arrayed-waveguide grating (AWG) multiplexers-demultiplexers. We measure the phase- and amplitude-error distributions of two different types of AWG and discuss their effects on the dispersion. The results show that the origin of the dispersion in the AWG is the low-order Fourier components of the symmetric phase and the antisymmetric amplitude errors. We also discuss the dependence of the dispersion on the passband shape in the presence of the same fabrication errors.