Soft Magnetic Properties of Fe/Fe-Hf-C Multilayered Films with High Thermal Stability

The magnetic and structural properties of rf sputter-deposited Fe/Fe-Hf-C multilayer films were investigated. Columnar growth of Fe was interrupted only when as-deposited Fe-Hf-C layers were amorphous. The Fe-Hf-C layers crystallize by annealing into ¿-Fe and HfC with small grains of size several nanometers. These multilayer films exhibited good soft magnetic properties (coercivity 26 A/m and permeability 3700) due to the small Fe grain sizes of each layer, as well as a high saturation flux density (approx. 2.0 T). Interdiffusion between layers during high-temperature annealing was suppressed by the formation of a strong bond between Hf and C in the Fe-Hf-C layers. Furthermore, fine HfC particles inhibited the growth of Fe grains. Thus a high permeability of more than 1000 was maintained even after annealing at 1023 K. In addition, near-zero-magnetostriction films were obtained by addition of a small amount of Co to the Fe-Hf-C larers, without any resulting decrease in permeability.