Magnetic, electronic transport, and calorimetric investigations of La1-xCaxCoO3 in comparison with La1-xSrxCoO3

The magnetic and electronic transport proper-ties and the specific heat of La1-xCaCoO3 (0.05 less than or equal to x less than or equal to 0.5) have been investigated. In the whole composition range, the Co atoms are in an intermediate-spin (IS) state, and a spin glass or a ferromagnetic ordered state appears at low temperatures. The conductivity increases with x, and shows a metallic temperature dependence for x greater than or equal to 0.4. The overall resemblance of the Ca substituted system with the Sr substituted one implies that the Ca substitution introduces holes into Co-O bonds as in the case of the Sr substitution. The present results reveal that the hole-doping, not the ionic size, is essential to stabilize the IS state of Co atoms in La1-xMxCoO3 with M being a divalent ion. The quantitative difference, lower T-C and less conductivity for M = Ca than M = Sr with the same x, suggests less mobility and/or less number of holes in the system with M Ca. The electronic specific heat coefficient, null for LaCoO3, increases sharply around x = 0.2 for M Sr and x = 0.25 for M = Ca, and saturates at higher concentrations. The observation indicates the presence of the Fermi surface in the deeply substituted specimens. The magneto-tran sport properties of the metallic specimens, especially a large amplitude of the side-jump scattering in the extraordinary Hall resistivity, are characteristic of itinerant ferromagnetic metals, which supports the double exchange mechanism in the present system.