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

氮化铁薄膜具有较大的饱和磁化强度和合理的矫顽力，是理想的记录材料。然而，为了使用这些薄膜作为实际的记录介质，必须克服几个问题，包括在高温下的相稳定性。因此，在本研究中，研究了氮化铁薄膜在高温下的相稳定性以及加热过程中发生的相或结构变化。为了评价溅射膜的性质，还对溅射膜的电阻率进行了测量，同时还对溅射膜的磁性进行了测量。VSM曲线)。主要研究结果如下：(1)通过控制氮气与氩气的比例、衬底温度、放电电压和放电电流，可以制备出氮化铁薄膜。研究还发现，在较高的衬底温度下制备的沉积膜显示出非常尖锐的x射线峰，并由更多的氮化铁膜组成，如ε相、γ′相和α′相。(2)通过原位电镜观察，研究了沉积态氮化铁薄膜在加热过程中的结构变化：溅射态薄膜中含有少量的α相，为局部分布的细颗粒。随着温度的升高，氮原子和铁原子开始发生位置有序，在加热过程中实现了完美有序的Fe_3N相。在不同的加热速率下，观察到从ε相到γ相的两种结构变化，这些特征可以在氮原子和铁原子的扩散和剪切位移的基础上得到很好的解释。考虑了加热过程中相分离和析出现象，较好地解释了不同热处理后VSM曲线的特征。对不同的沉积铁膜进行了沉积膜的电阻率测量。结果表明，在较高的溅射气体压力下制备的沉积膜的电阻率略高。考虑到在沉积薄膜中形成的晶界周围发生了质变，这很好地解释了这一点。对沉积薄膜进行电测量是评价薄膜性能的有效方法。进一步的详细研究正在进行中。少

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