Soft Magnetic Properties of Fe-N Thin Films Sputtered in Ar+N2 Plasma

Excellent soft magnetic properties, including a high μ
_eff
(2000 at 5 MHz) and high B
_s
(2.2 T), were obtained from Fe films fabricated by the facing-target dc magnetron sputtering method in Ar+N
₂
plasma and annealed at 300°C. A (110) preferred grain orientation and reduction of grain sizes to below 150 Å were observed in these films. The lattice spacing of (110) planes was found to be increased by 0.28% over the bulk value. The total anisotropy energy in the (110) plane of crystal grains was calculated, taking into consideration the magnetostrictive anisotropy due to lattice strain. The results show that the total anisotropy decreases and takes on a minimum at a (110) lattice spacing increased by 0.28%, in a change from bec to bet structure. This value agrees well with the expansion of the bec lattice of films exhibiting high μ
_eff
. Excellent soft magnetic properties were obtained by decreasing the total anisotropy of grains due to lattice strain and by reduction of grain sizes, and were not related to the magnetostriction of the films.