THE EFFECT OF HEATING ON THE MAGNETIC-PROPERTIES OF FE3O4 FINE PARTICLES

Ac susceptibility measurements in the temperature range 200 K less-tha n-or-equal-to T less-than-or-equal-to 300 K are reported for samples o f Fe3O4 fine particles heat treated at different temperatures. Also, d c magnetization measurements are reported at room temperature in magne tic fields up to 1.5 T. Information about the distribution functions o f blocking temperatures and particle sizes, and about the effective an isotropy constants, are deduced. The effect of heating on the magnetic properties and on interparticle interactions are discussed. The tempe rature dependence of the inverse susceptibility for T > T(B) (T(B) = t he effective blocking temperature) indicates the existence of a Curie- Weiss-type behavior, with antiferromagnetic coupling, in samples treat ed at T less-than-or-equal-to 300 K.