Transport and Magnetic Properties of R1-xAxCoO3 (R = La, Pr and Nd; A = Ba, Sr and Ca)

Transport and magnetic measurements have been carried out on perovskite Co-oxides R 1- x A x CoO 3 (R = La, Pr, and Nd; A = Ba, Sr and Ca; 0≤ x ≤0.5: All sets of the R and A species except Nd 1- x Ba x CoO 3 have been studied.). With increasing the Sr- or Ba-concentration x , the system becomes metallic ferromagnet with rather large magnetic moments. For R = Pr and Nd and A = Ca, the system approaches the metal–insulator phase boundary but does not become metallic. The magnetic moments of the Ca-doped systems measured with the magnetic field H =0.1 T are much smaller than those of the Ba- and Sr-doped systems. The thermoelectric powers of the Ba- and Sr-doped systems decrease from large positive values of lightly doped samples to negative ones with increasing doping level, while those of Ca-doped systems remain positive. These results can be understood by considering the relationship between the average ionic radius of R 1- x A x and the energy difference between the low spin and intermediate spin states....

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