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

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