RESUMEN
A novel quadruple perovskite oxide CeCu3Co4O12 has been synthesized in high-pressure and high-temperature conditions of 12 GPa and 1273 K. Rietveld refinement of the synchrotron X-ray powder diffraction pattern reveals that this oxide crystallizes in a cubic quadruple perovskite structure with the 1:3-type ordering of Ce and Cu ions at the A-site. X-ray absorption spectroscopy analysis demonstrates the valence-state transitions in the ACu3Co4O12 series (A = Ca, Y, Ce) from Ca2+Cu3+3Co3.25+4O12 to Y3+Cu3+3Co3+4O12 to Ce4+Cu2.67+3Co3+4O12, where the electrons are doped in the order from B-site (Co3.25+ â Co3+) to A'-site (Cu3+ â Cu2.67+). This electron-doping sequence is in stark contrast to the typical B-site electron doping for simple ABO3-type perovskite and quadruple perovskites CaCu3B4O12 (B = V, Cr, Mn), further differing from the monotonical A'-site electron doping for Na1-xLaxMn3Ti4O12 and A'- and B-site electron doping for AMn3V4O12 (A = Na, Ca, La). The differences in the electron-doping sequences are interpreted by rigid-band models, proposing a wide variety of electronic states for the complex transition-metal oxides containing the multiple valence-variable ions.
RESUMEN
The extraordinary Hall resistivity rho(xy) and the magnetization M of a canonical spin glass AuFe (8 at.% Fe) were measured simultaneously as functions of temperature with the best care to the thermal and the magnetic field hysteresis. The data of rho(xy) show an anomaly at the spin glass transition temperature T(g) and have different zero field cooling (ZFC) and field cooling (FC) measurements below T(g). Moreover, the value of rho(xy)/M, which represents the chiral susceptibility of the system in the present case, also shows the difference between ZFC and FC measurements. The results are consistent with the predictions of the chirality scenario of canonical spin glasses by Kawamura.