Abstract
A.Pr1+xBa2-xCu3O7-y system The Pr L3-edge and Cu K-edge X-ray absorption near-edge strucutre (XANES) data and magnetic data for the insulating PrBa2Cu3O7-y (y = 0.05, 0.11, 0.21, 0.26, 0.57, 0.62, 0.79) and Pr1+xBa2-xCu3O7-y (x = 0.2, 0.4, 0.6, 0.8, 1.0) samples are reported. The anomalous antiferromagnetic Néel temperature TN decreases monotonically from 18.5 K for oxygenated compound (y = 0.05) to 11 K for oxygen-reduced compound (y = 0.79). The Pr L3-edge (2p-5d transition) XANES data indicate that the formal Pr valence decreases from 3.17 for y = 0.05 to 3.01 for y = 0.79. The Cu K-edge (1s-4p transition) XANES data show that the threshold energy (edge inflection point) shifts from 8982.2 eV for y = 0.05 to 8980.2 eV for y = 0.79. A systematic variation was found that peak A and peak B of Cu K-edge XANES intensities increase with oxygen content (hole doping). The correlation among Pr/Cu valence, structure, Pr-O bond length, and TN(Pr) are discussed. B.Ca1-xSrxRuO3 system Ru L3-edge and O K-edge X-ray absorption near-edge spectra (XANES), powder X-ray Rietveld analysis and magnetic studies were performed on the Ca1-xSrxRuO3 system (0 < x < 1) and BaRuO3, where CaRuO3 is an exchange-enhanced paramagnetic metal, SrRuO3 is an itinerant ferromagnet (TC ~ 160 K) and BaRuO3 is a normal paramagnetic metal with no local moment. XANES and X-ray diffraction data indicate that all samples are very close to the stoichiometric 113 compositions with tetravalent Ru (most of the four 4d electrons in t2g bands) and stronger RuO6 octahedral distortion near the CaRuO3 region (space group Pbnm). Ferromagnetic spin fluctuation was obvious in the paramagnetic region (x < 0.2) from low temperature initial magnetization and hysteresis studies. Anomalous field-dependent behavior with small, unsaturated magnetic moment was also observed in the itinerant ferromagnetic region. Magnetic relaxation data M(t) show anomalous behavior. Ru L3-edge XANES data with larger absorption intensity with increasing Sr substitution indicates larger density of states near the Fermi level eF and smaller orthorhombic lattice distortion. The correlation among structural distortion, itinerant ferromagnetism, ferromagnetic spin fluctuation, and band structure variation will be discussed.