On the role of a magnetic coupling between crystalline grains in nanocrystalline alloys

Basic differences between magnetic properties of Fe-Cu-Nb-Si-B and Fe-Cr-Cu-Nb-Si-B nanocrystalline alloys (magnetically harder fine particles embedded in a soft magnetic amorphous matrix) are explained in terms of a magnetic coupling between nanocrystalline grains. It has been shown that in the magnetic behavior of Finemet alloy with a high crystalline fraction, the ferromagnetic exchange interactions play the crucial role even at temperatures above the Curie point of the amorphous phase. Much weaker magnetic interactions in Fe-Cr based alloys with low crystalline contents are responsible for the hardening of the material and rapid magnetic decoupling of the grains with increasing temperature.