Stress-induced magnetic anisotropy in nanocrystalline FeCuNbSiB alloy

Nanocrystalline Fe73.5Cu1Nb3Si13.5B9 (at%) shows excellent soft magnetic properties. The ultrafine grain structure consisting of FeSi grains with an average grain diameter of about 12 nm embedded in an amorphous matrix is produced by annealing melt-spun amorphous ribbons above the crystallization temperature. Annealing of the amorphous and nanocrystalline Fe73.5Cu1Nb3Si13.5B9 ribbons under mechanical stress induces magnetic anisotropy. The easy axis is transversal to the tensile stress direction. Anisotropies up to about K-u = 8000 J/m(3) have been observed. The annealing parameters and the measuring temperature are varied in order to obtain information on the microstructural mechanism responsible for the stress-induced anisotropy. In addition, the relaxation behaviour of the induced anisotropy is investigated. The induced anisotropy can be explained by atomic pair ordering processes in the FeSi nanocrystals as well as by a magneto-elastic anisotropy of the FeSi grains due to internal stresses.