Spin state crossover and colossal magnetoresistance in barium-doped cobaltites

Abstract

Investigation of the crystal structure, magnetic and transport properties of both the stoichiometric and anion-deficient Ba2+-doped lanthanum cobaltites was performed. Anomalous temperature behavior of the structural parameters as well as the magnetic, electrical and magnetotransport characteristics was found due to concurrence of magnetic interactions. It was shown that the anion deficiency stabilized insulating antiferromagnetism and destroyed conductive ferromagnetism. We argue that the ferromagnetism developed on the basis of Co3+/Co4+ ions with one eg electron (i.e., possessing the intermediate-spin (IS) state), while the presence of two eg electrons (corresponding to the high-spin (HS) state) favored the antiferromagnetic order. The covalent component of the chemical bond stabilized an electronic configuration close to the IS state. The colossal magnetoresistance arose at a concentration or temperature boundary (where ferromagnetic and antiferromagnetic phases or clusters coexist) as a result of the field-induced spin transition from mixed HS/low-spin state (predominantly antiferromagnetic and insulating) to IS (predominantly ferromagnetic and highly conductive) state.