Correlation between nanocrystalline and magnetic structure of Co-based alloys with the induced transverse magnetic anisotropy

Abstract

The magnetic domain structure is a specific property of ferromagnetic materials influencing their main magnetic properties. The aim of this work was to determine a relationship between nanocrystalline and the domain structure observed by means of magneto-optic Kerr effect on the surface of the Fe14.7Co58.8Cu1Nb3Si13.5B9 and Fe13.8Co65Cu0.6Nb2.6Si9B9 toroidal cores, and the induced transverse magnetic anisotropy Ku. The transverse magnetic anisotropy was induced in the Fe14.7Co58.8Cu1Nb3Si13.5B9 and Fe13.8Co65Cu0.6Nb2.6Si9B9 amorphous cores by annealing them at the temperature of 460 °C, under an external magnetic field of 500 kA/m. It was found that the appearance of nanocrystalline phase in the Fe13.8Co65Cu0.6Nb2.6Si9B9 alloy resulted in considerable increase of the magnetic anisotropy constant to 900 J/m3 already after 40 minutes of heating, whereas the nanocrystallization process in the Fe14.7Co58.8Cu1Nb3Si13.5B9 alloy proceeded much slower (after 240 minutes of heating the content of nanocrystalline phase was at the level of about 18%, and the induced magnetic anisotropy constant reached 190 J/m3). Observations of the domain structure were also made showing that the 180° domains were obtained in the Fe14.7Co58.8Cu1Nb3Si13.5B9 alloy only after 240 min of heating, whereas similar structure was observed in the Fe13.8Co65Cu0.6Nb2.6Si9B9 alloy already after 40 min of treatment.