Melting of Pb Charge Glass and Simultaneous Pb-Cr Charge Transfer in PbCrO3 as the Origin of Volume Collapse.

A metal to insulator transition in integer or half integer charge systems can be regarded as crystallization of charges. The insulating state tends to have a glassy nature when randomness or geometrical frustration exists. We report that the charge glass state is realized in a perovskite compound PbCrO3, which has been known for almost 50 years, without any obvious inhomogeneity or triangular arrangement in the charge system. PbCrO3 has a valence state of Pb(2+)(0.5)Pb(4+)(0.5)Cr(3+)O3 with Pb(2+)-Pb(4+) correlation length of three lattice-spacings at ambient condition. A pressure induced melting of charge glass and simultaneous Pb-Cr charge transfer causes an insulator to metal transition and ∼10% volume collapse.

Characteristic oxygen K-edge circular dichroism spectra of amino acid films by improved measurement technique.

Circular dichroism (CD) spectroscopy in the soft x-ray energy region is a new tool to study the local structure of chiral materials. In this paper, we introduce a method to measure high-quality CD spectra in the oxygen K-edge energy region. Characteristic CD spectra of thin films of the amino acids L-tyrosine and L-aspartic acid are reported and compared with those of films of L-alanine and L-serine. The signals from the oxygen 1s → π∗ transitions of COO-, which is a common moiety in these amino acids, reflect the local geometry of each amino acid.

Application of magnetic Compton scattering for spin-specific magnetic hysteresis measurement.

An application of magnetic Compton scattering as a new tool to measure a spin-specific magnetic hysteresis (SSMH) loop is introduced and its validity demonstrated. The applied magnetic field dependence of the integrated intensity of magnetic Compton scattering spectra, which reflect only the spin-dependent magnetic properties of magnetically active electrons, was interpreted as the spin-specific hysteresis. The spin magnetization of amorphous Tb(33)Co(67) film was observed and its SSMH loop exhibited qualitative agreement with the ordinal magnetic hysteresis loop measured using a conventional vibrating sample magnetometer.

Antiferromagnetic interaction between A'-site Mn spins in A-site-ordered perovskite YMn3Al4O12.

The A-site-ordered perovskite YMn(3)Al(4)O(12) was prepared by high-pressure synthesis. Structural analysis with synchrotron powder X-ray diffraction data and the Mn L-edges X-ray absorption spectrum revealed that the compound has a chemical composition Y(3+)Mn(3+)(3)Al(3+)(4)O(2-)(12) with magnetic Mn(3+) at the A' site and non-magnetic Al(3+) at the B site. An antiferromagnetic interaction between the A'-site Mn(3+) spins is induced by the nearest neighboring Mn-Mn direct exchange interaction and causes an antiferromagnetic transition at 34.3 K.

Various valence states of square-coordinated mn in a-site-ordered perovskites.

A-site-ordered perovskites LaMn(3)Cr(4)O(12) and LaMn(3)Ti(4)O(12) were synthesized under high-pressure and high-temperature conditions. The charge formula of LaMn(3)Cr(4)O(12) was found to be LaMn(3+)(3)Cr(3+)(4)O(12) with Mn(3+) at the square-coordinated A site. The valence of the A-site Mn ions in LaMn(3)Ti(4)O(12) appeared to be less than +2, and the charge combination in this compound seemed to be LaMn(1.67+)(3)Ti(4+)(4)O(12). Although the square-coordinated A site in A-site-ordered perovskites has been widely known to be occupied by Jahn-Teller active Mn(3+), the present results show that the valence of Mn at the A site can vary from +3 to possible +1.67.