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

• Published in: Journal of the Physical Society of Japan Vol. 72; no. 4; pp. 873 - 878
• Main Authors: MASUDA, Hiroyasu, FUJITA, Toshiaki, MIYASHITA, Takeshi, SODA, Minoru, YASUI, Yukio, KOBAYASHI, Yoshiaki, SATO, Masatoshi
• Format: Journal Article
• Language: English
• Published: Tokyo Institute of Pure and Applied Physics 01-04-2003; Physical Society of Japan; The Physical Society of Japan
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Conductivity phenomena in semiconductors and insulators; Electronic transport in condensed matter; Exact sciences and technology; Magnetic properties and materials; Mobility edges ; hopping transport; Physics; Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.); Inorganic compounds; Electrical conductivity; Pressure effects; Metal-insulator transition; Rare earths Oxides; Cobalt oxides; Rare earth compounds; Alkaline earth metals Oxides; Thermoelectric power; PrCoO3; Anomaly; Chemical composition; Ferromagnetism; Quaternary compounds; Magnetization; Phase transformations; Magnetic ordering; Transition element compounds; Magnetic field effects; Perovskites; Ionic radius; Experimental study; hole doping; spin state change; Transport processes; transport and magnetic properties; Spin state
• ISSN: 0031-9015; 1347-4073

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.