Magnetic and transport properties of the layered perovskite system Sr2-yYyCoO4 (0≤y≤1) -: art. no. 064401

Layered perovskite cobalt oxides Sr2-yYyCoO4 (y=0, 0.1, 0.3, 0.5, 0.67, 0.83, and 1) were synthesized under high pressure and high temperature conditions. Structure refinement revealed that these compounds crystallize in K2NiF4-type structures with space group I4/mmm. The parent compound Sr2CoO4 undergoes a ferromagnetic transition with T-c=255 K. The T-c decreases with increasing y to 150 K for y=0.5, and ferromagnetism was not observed for y >= 0.67. Assessment of spin states for Co3+ and Co4+ ions suggested strongly that both are present as intermediate spin states when y <= 0.67 at least for the higher temperature range above T-c. Fairly large negative magnetoresistance was observed for Sr2CoO4 in the vicinity of T-c and in the lower temperature region.