Exchange bias in granular CoO layers due to random magnetic anisotropy

The structural and magnetic properties of granular CoO layers have been investigated by scanning tunneling microscopy (STM) and magnetization measurements. The CoO shows a strong exchange anisotropy which is attributed to an interaction between the antiferromagnetic order and uncompensated spins in the antiferromagnetic material. No appreciable amount of ferromagnetic material is needed to establish characteristic properties of exchange bias such as the shift of the magnetic hysteresis loop. A new approach to the problem of exchange anisotropy is suggested which is based on random magnetic anisotropy of CoO nanoparticles.