Possible ferrimagnetic ordering in single-crystals at low temperatures

Single-crystals of the novel mixed valent cobaltite Y BaCo4O7+δ have been synthesized. Careful magnetization measurements gave evidence of a ferrimagnetic phase with a T C ≈ 50 K and a large coercive field of ∼1 T at 5 K. As no substitution of a divalent cation for yttrium was realized, it is possible that the Co2+/Co3 ratio to be modified only by the presence of extra oxygen atoms in the tetrahedral network.