Cr enhanced ferromagnetism in La0.5Ba0.5CoO3 due to possible double-exchange interaction

The magnetic studies have been carried out on the R-doped La0.5Ba0.5Co0.9R0.1O3 (R = Cu, Zn, Cr, Ni, Ti and Ru) cobaltites. X-ray absorption near-edge structure (XANES) proves these ions are in the valence state of Cu2+, Zn2+, Cr3+, Ni3+, Ti4+ and Ru4+. Magnetic moment calculation shows both Co3+ and Co4+ hold in the intermediate spin state. Based on the ratio of Co3+/Co4+, the average B-site size, the tolerance factor and electron itinerancy, the different influence of these ions on the magnetism were discussed. Among all these ions, Cr3+ gives an extraordinary effect of enhancing TC a lot. It is attributed to the Co-O-Cr exchange interaction, which is confirmed by the electron spin resonance spectra. The typical magnetotransport behavior implies a double-exchange property of this exchange interaction.