Neutron diffraction study of a layered cobalt oxide SrCo6O11

Abstract The magnetic structure of a hexagonal layered cobalt oxide SrCo 6 O 11 , which exhibits a 1/3 magnetization plateau and a concomitant large negative megnetoresistance below 20 K, was studied by means of neutron diffraction measurements and Rietveld analysis. It has been found that only the trigonal bipyramidal site carries a localized moment, which corresponds to S =2, and that the moment has an Ising-like anisotropy along the c -axis. These moments are aligned ferromagnetically in the c -plane, while the interlayer coupling is field dependent. The 1/3 magnetization plateau reflects a field-induced ferrimagnetic alignment along the c -axis like “up–up–down–up–up–down”. We interpret this complex spin structure as resulting from competition of an antiferromagnetic superexchange interaction between the nearest ferromagnetic layers and carrier-mediated, ferromagnetic interactions.