Magnetic properties of monodispersed Co/CoO clusters

Monodispersed Co/CoO cluster assemblies with the mean cluster sizes of 6 an d 13 nm have been prepared by a plasma-gas condensation type cluster beam d eposition apparatus. We measured the effects of the oxygen gas flow rate du ring deposition, temperature, and cluster size on the coercivity and hyster esis loop shift induced by field cooling. The large exchange bias field (10 .2 kOe) and coercivity (5 kOe) were observed at 5 K for the monodispersed C o/CoO cluster assembly with d=6 nm. The correlations between unidirectional anisotropy and uniaxial anisotropy, training effect and magnetic relaxatio n can be interpreted by the hypothesis of a spin disorder in the interfacia l layer between the antiferromagnetic CoO shell and the ferromagnetic Co co re.