Magnetic property of oxide passivated Co nanosized particles dispersed in two dimensional plane

The particle size dependence of Neel temperature was investigated in a thin CoO shell of an oxide passivated Co particle. In addition to the blocking effect of the exchange anisotropy interaction, the influence of the magneti c dipole interaction between neighbouring Co cores to the blocking temperat ure TB was examined by measuring the zero field cooling magnetic susceptibi lity in dense oxide passivated nanosized Co particles dispersed uniformly o n two dimensional plane without coagulation. The blocking temperature domin ated by the dipole-dipole interaction was discussed in relation to the tran sition temperature to the spin-glass like collective state.