Induced magnetic anisotropy in Si-free nanocrystalline soft magnetic materials: A transmission x-ray diffraction study.

In order to better understand the origin of field-induced anisotropy (K_u) in Si-free nanocrystalline soft magnetic alloys, the lattice spacing of the bcc-Fe phase in nanocrystalline Fe_94-xNb₆B_x (x=10, 12, 14) alloys annealed under an applied magnetic field has been investigated by X-ray diffraction in transmission geometry (t-XRD) with the diffraction vector parallel and perpendicular to the field direction. The saturation magnetostriction (λ_s) of nanocrystalline Fe_94-xNb₆B_x was found to increase linearly with the volume fraction of the residual amorphous phase and is well described by taking into account the volume-weighted average of two local λ_s values for the bcc-Fe nanocrystallites (-5±2 ppm) and the residual amorphous matrix (+8±2 ppm). The lattice distortion required to produce the measured K_u values (~100 J/m³) was estimated via the inverse magnetostrictive effect using the measured λ_s values and was compared to the lattice spacing estimations made by t-XRD. The lattice strain required to produce K_u under the magnetoelastic model was not observed by the t-XRD experiments and so the findings of this study suggest that the origin of magnetic field induced K_u cannot be explained through the magnetoelastic effect. [ABSTRACT FROM AUTHOR]