Metastable Fe nitrides with high Bs prepared by reactive sputtering

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 (PN2) 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 (σs) of about 240 emu/g exceeding the value for Fe can be obtained around PN2=0.1∼1×10−3 Torr. From thermomagnetization and x-ray analyses the increased σs is attributed to Fe16N2 compound, but the coexistence of bcc Fe and Fe4N prevents reaching the σs 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).