On the intergranular coupling in soft nanocrystalline materials

The magnetic softness of nanocrystalline materials prepared from amorphous precursors is attributed to the average of the local magnetocrystalline anisotropy of the individual crystallites. In the present paper we have studied the effective magnetic anisotropy of Fe-based nanocrystalline samples with different microstructures. These microstructures were produced by using different heating rates when crystallizing the precursor material by means of continuous heating treatments. From the results of our study of the magnetic properties of the samples, carried out from the measurement of the bias held dependence of the transverse susceptibility, it was possible to discern the occurrence of intergranular coupling and to evaluate the typical dimensions of the coupled units. Since these dimensions were larger than the characteristic length of the microstructure, we suggest that the enhancement of the soft properties is linked to the decrease of the microstructure-magnetization interactions originating in large units of coupled magnetic moments.