Origin of the perpendicular anisotropy in amorphous ${\mathrm{Fe}}_{82}$${\mathrm{B}}_{12}$${\mathrm{Si}}_6$ ribbons

The magnetic anisotropy in amorphous ${\mathrm{Fe}}_{82}$ ${\mathrm{B}}_{12}$ ${\mathrm{Si}}_6$ (METGLAS ® 2605S) has been studied by the determination of both surface and bulk properties using Mössbauer, x-ray, and density measurements. Upon annealing above 650 K, a substantial anisotropy with an easy direction perpendicular to the ribbon plane develops. It is proposed that the origin of this out-of-plane anisotropy, also observed for other amorphous ribbons, is a compressive stress from the formation of higher-density crystalline surface layers. The compressive stress produces the perpendicular anisotropy in the ribbon bulk through positive magnetostriction.