Exchange Anisotropy in Oxidized Iron-Cobalt Particles

Oxidized single-domain particles of iron-cobalt were found to exhibit properties characteristic of an exchange interaction between ferromagnetic and antiferromagnetic phases. After cooling in a magnetic field,the normal hysteresis loop was shifted along the magnetization axis. Rotational hysteresis and torque values show maxima with increasing field and indicate effective unidirectional fields of ∼20000 oe. The data are consistent with an exchange model similar to that of Meiklejohn and Bean, but the exchange and antiferromagnetic anisotropy fields are larger than those found for the Co-CoO system.