Abstract
Magnetization measurements of ∼150Å size Cr2O3 particles prepared by chemical precipitation are reported. Zero-field-cooled (ZFC) susceptibility exhibits a peak characterizing a blocking behaviour at TB≈40K. Above the bifurcation point of ∼160K the reversal magnetizations vary linearly with H, whereas below it both ZFC and field-cooled hysteresis loops exhibit large coercivities. Exchange fields of ∼2000Oe are also observed at low temperatures. Magnetization relaxes according to the equation M(t)=M(t0)[1−S(T)ln((t+t0)/τ0)]. Magnetic viscosity S(T) is found to be linear for T⩽10K.