On magnetization mechanisms in iron-based nanocrystalline alloys

The Fe-Cu-Nb-Si-B nanocrystalline alloys (FINEMET) are well known because of their excellent soft magnetic properties. Substitution of several atomic percent of Fe by Cr dramatically changes magnetic properties of the alloy, though its microstructure remains nanocrystalline. A comparison between magnetic properties of the Fe73.5Cu1Nb3Si15.5B7 and Fe66Cr8Cu1Nb3Si13B9 nanocrystalline alloys with different crystalline fractions is presented. The measurements of the coercive field, static and dynamical magnetic permeabilities as well as Barkhausen effect give evidence that magnetic behaviours of these alloys are dominated by two different magnetization mechanisms: domain wall movements in FINEMET and rotations in Fe-Cr-Cu-Nb-Si-B alloy. The increase of the coercivity and magnetic anisotropy in the alloys with Cr addition results from anisotropic properties of the grains which are weakly coupled through the intergranular phase because of lower saturation magnetization of the matrix in comparison with that in the Fe-Cu-Nb-Si-B nanocrystalline alloys.