Crystal size and magnetic field effects in Co3 O4 antiferromagnetic nanocrystals

We report magnetism of spinel Co3 O4 nanocrystals with average diameters of ∼25 and ∼100□nm under magnetic fields up to 50 kOe. The nanoparticles were controlled to be cubic in shape. In the smaller nanocrystal sample (d∼25□nm), a spontaneous magnetic moment increased steeply below the Néel point, TN =32□K of the bulk sample, whereas similar to bulk samples the larger crystal sample (d∼100□nm) exhibited a maximum in magnetization around TN. A spin-glass-like behavior in magnetization was observed at Tt =10□K at lower magnetic fields, whereas above H=30□kOe, this behavior disappeared.