Possible ferrimagnetic ordering in YBaCo4O7+δ single-crystals at low temperatures

Abstract Single-crystals of the novel mixed valent cobaltite Y BaCo 4 O 7+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 Co 2+ /Co 3 ratio to be modified only by the presence of extra oxygen atoms in the tetrahedral network.