FERROMAGNETIC INTERACTIONS IN NANOSTRUCTURED SYSTEMS WITH 2 DIFFERENTCURIE TEMPERATURES

We study the exchange interactions between ferromagnetic grains disper sed in a paramagnetic amorphous matrix. This interaction becomes very important for high-density packing of the grains and also when the amo rphous matrix is near its Curie temperature. We obtain analytical resu lts based on a mean-field approximation and also perform a Monte Carlo simulation. We use both procedures to estimate the ordering temperatu re as a function of the effective intergrain separation. The theoretic al predictions are compared with experimental results for the Fe77B18N b4Cu nanocrystalline alloy.