Effect of boron on the field-induced magnetic anisotropy in Fe-based soft magnetic nanostructures

The field-induced magnetic anisotropy ( K u ) and the hyperfine interactions in nanocrystalline Fe 94 − x Nb 6 B x ( x = 10 , 12, and 14) alloys have been investigated with particular attention paid to the origin of K u in the bcc-Fe/amorphous soft magnetic nanostructures. The Fe 57 Mössbauer spectra from the Fe-Nb-B alloys suggest that the solute content in the residual amorphous phase remains unchanged while the volume fraction of the residual amorphous phase ( V am ) , increases linearly with B content. This indicates that V am is governed by the lever rule over the partial equilibrium between the primary bcc-Fe and the residual amorphous phases. Both the saturation magnetization ( J s ) and K u were confirmed to vary linearly with V am and they are well described by taking into account the volume-weighted average of J s = 2.1 T and K u = 127 J ∕ m 3 for the bcc-Fe nanocrystallites and J s = 1.0 T and K u = 76 J ∕ m 3 for the residual amorphous matrix. The relatively large K u value estimated for the bcc nanocrystallites may be attributed to a possible local tetragonal distortion induced by the interstitial B atoms.