Soft magnetic properties and microstructure of nanocrystalline Fe-Hf-N sputtered films

Magnetic properties, structure and electrical resistivity (ρ) of Fe-Hf-N films with a compositional range of 10-17 at.% Hf and 9-28 at.% N were investigated. In an as-deposited state, the high permeability (μ´) above 700 at 10 MHz is obtained in the compositional range of about 12-14 at.% Hf and about 9-19 at.% N. The highest μ´ of 1200 is achieved for Fe₇₂Hf₁₃N ₁₅ film consisting of the nanoscale BCC grains and the amorphous phase with the high Curie temperature (T_c) due to higher contents of Hf and N than those in the BCC phase. The soft magnetic properties are presumably caused by the reduced effective anisotropy resulting from the effect of the nanoscale BCC grains and the rather high magnetization of the amorphous phase at room temperature which does not inhibit the exchange coupling between the grains. Fe₆₅Hf₁₁N₂₄ film with the mixed structure exhibits the saturation magnetic flux density (B₃) of 1.2 T and the flat μ´ characteristics of 1000 up to 100 MHz after annealing at 673 K for 3 hrs under an uniaxial field. This excellent Cc characteristics originates in the rather large magnetic anisotropy field (H_k) of 510 A/m and the high ρ of 2.7 μΩm m which comes from the Hf and N-riched amorphous phase