Effect of Si on the field-induced anisotropy in Fe-rich nanocrystalline soft magnetic alloys

Abstract The field-induced magnetic anisotropy ( K u ) and hyperfine interactions have been investigated for nanocrystalline Fe bal. B 14∼14.8 Si x Cu 1.5 (x = 0, 1, 2 and 4) alloys. 57 Fe Mossbauer spectroscopy was used to quantify the Si contents and volume fractions of the amorphous and bcc-Fe(Si) phases after nanocrystallisation. This information was then used to estimate the local K u contribution from the bcc-Fe(Si) phase. The bulk K u value of these nanocrystalline alloys showed an increase from 40 ± 5 J/m 3 to 69 ± 5 J/m 3 with increasing Si content from 0 to 4 at%. The local K u of the bcc-Fe(Si) phase was found to increase in line with Si content, as predicted by the well-known directional pair ordering model and showed a large value of 172 ± 14 J/m 3 for a local Si content of around 6 at%. The addition of Si to Fe-rich nanocrystalline alloys is widely perceived as an effective means for improving magnetic softness. However, the findings of this study imply that small additions of Si to Fe-rich nanocrystalline alloys may result in undesirable effects if the crystalline volume fraction is especially large.