Interacting magnetic defects in a random antiferromagnetic matrix: A spin-glass-like model of exchange bias

The magnetic behavior of granular CoO layers and granular CoO/ferromagnet bilayers has been investigated by magnetization and hysteresis loop measurements. The net magnetization in the CoO is attributed to magnetic defects due to the particle boundaries and imperfections within the whole particle volume. The CoO particle layers and the CoO/ferromagnet bilayers show characteristic exchange bias effects and a similar magnetization reversal behavior. On the basis of the experimental results, an approach to the problem of exchange bias is suggested. It relies on interacting magnetic defects which are embedded in an antiferromagnetic matrix with a high degree of disorder in the spatial distribution of the magnetic sublattices. The matrix is provided by the antiferromagnetic order within the particles, the spatial disorder by their random anisotropy.