Metastable Fe nitrides with high Bs prepared by reactive sputtering

Abstract

Preparation of thick films or bulk formed materials of Fe₁₆N₂ compound has been attempted using a high rate reactive‐sputtering technique. As for the reactive gas, N₂ was introduced with various pressures (P_N2) into the chamber by mixing with Ar gas of about 10⁻² Torr. About 0.5‐mm thick bulk deposits were obtained through the continuous running with a 1000 Å/min rate. It has been found that the magnetization (σ_s) of about 240 emu/g exceeding the value for Fe can be obtained around P_N2=0.1∼1×10⁻³ Torr. From thermomagnetization and x‐ray analyses the increased σ_s is attributed to Fe₁₆N₂ compound, but the coexistence of bcc Fe and Fe₄N prevents reaching the σ_s to the expected maximum value 298 emu/g of Fe₁₆N₂. From the application point of view, the presently obtained Fe nitrides are interesting in their coercivities and are useful for semihard magnets with high Vicker’s hardness (about 700 Hv).