Annealing effects on the magnetic properties of nanocrystalline zinc ferrite

The effects of annealing on the magnetic properties of nanocrystalline ZnFe2O4 have been studied. The as-prepared sample ZnFe2O4 With the particle size of about 3 nm presents a relatively low blocking temperature of about 6 K as derived from the peak of the zero-field-cooled curve measured in a SQUID. Under the effect of annealing, the particle size significantly increases. Up to the annealing temperature of 800degreesC, the blocking temperature is found to increase with increasing particle size, whereas the (effective) anisotropy constant K-A decreases. The latter effect is attributed to the smaller contribution of the surface anisotropy when the particle size increases. (C) 2002 Elsevier Science B.V. All rights reserved.