Study of Phase Changes and Physical Properties in Iron Nitride Films Prepared by Reactive Sputtering

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Iron nitride films are premising recording materials because of large saturation mangetization with a reasonable coercive force. In order to use these films as practical recording media, however, several problems including phase stability at elevated temperatures must be overcome. Therefore, in this study phase stability of iron nitride films subjected to elevated temperatures was examined together with phase or structural change taking place during heating process. Electric resistivity measurement of as-sputtered films was also done in order to evaluate a nature of film property, together with the measurement of magnetic property .(i.e.VSM curve). Main results are as follows:(1) Every iron nitride films were found to be prepared by controlling the ratio of nitrogen gas to argon gas, the substrate temperature, discharge voltage and discharge current. It was also found that as-deposited films prepared at elevated substrate temperatures showed very sharp X-ray peaks and consisted of stab … More le iron nitride films such as epsilon-, gamma'- and alpha- phases.(2) A structural change of as-deposited iron nitride films during heating process was investigated by in-situ electron microscopy observations: as-sputtered films contained a small amount of alpha-phase as locally distributed fine particles. Both nitrogen and iron atoms began to take place an site ordering with increasing temperature, and perfect ordered Fe_3N phase was realized during heating process. Two kinds of structural change from the epsilon phase to gamma' phase were observed for different heating rates: These features are well explained on the basis of both diffusion and shear displacement of nitrogen and iron atoms. Characteristics of VSM curves measured after various heating treatments were well explained by considering phase separation and precipitation occurred during heating process. Electric resistivity measurement of as-deposited films was done for various as-deposited iron films. It was found that as-deposited films prepared under higher sputtering gas pressures showed a slightly higher resistivity. This was well explained by considering that a qualitative change took place around grain boundaries formed in as-deposited films. The electric measurement of as-deposited films was found to be effective for evaluation of film property. Further detailed study is in progress. Less