Magnetic and Transport Properties and Spin States of Layered Cobalt Oxides Sr2-xHoxCoO4 (0 ≤ x ≤ 1.0)

Layered cobalt oxides of Sr 2-x Ho x CoO 4 (0 ≤ x < 1.0) with square-lattice CoO 2 sheets (K 2 NiF 4 -type structure) were synthesized under high pressure and high temperature conditions. Ferromagnetism with Curie temperature T C of ∼ 255 K was observed in the Sr 2 CoO 4 compound. The Ho substitution effects on the magnetic and transport properties, and spin states of Co were systematically studied for the Sr 2-x Ho x CoO 4 system. Large magnetore-sistance was also observed at both low temperatures and vicinity of T C . Assessment of spin state for the CD 3+ (produced by introduction of Ho 34 for Sr 2+ ) and Co 4+ inns suggested that both are presented as intermediate-spin states.