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

• Main Authors: Masuda, Hiroyasu, Fujita, Toshiaki, Miyashita, Takeshi, Soda, Minoru, Yasui, Yukio, Kobayashi, Yoshiaki, Sato, Masatoshi
• Format: Journal Article
• Language: English
• Published: 21-02-2003
• Subjects: Physics - Materials Science; Physics - Strongly Correlated Electrons
• DOI: 10.48550/arxiv.cond-mat/0302435

Transport and magnetic measurements have been carried out on perovskite
Co-oxides R1-xAxCoO3 (R=La, Pr, and Nd; A=Ba, Sr and Ca; 0<x<0.5: All sets of
the R and A species except Nd1-xBaxCoO3 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 R1-xAx and the
energy difference between the low spin and intermediate spin states. We have
found the resistivity-anomaly in the measurements of Pr1-xCaxCoO3 under
pressure in the wide region of x, which indicates the existence of a phase
transition different from the one reported in the very restricted region of
x~0.5 at ambient pressure [Tsubouchi et al. Phys. Rev. B 66 (2002) 052418.]. No
indication of this kind of transition has been observed in other species of R.