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，是制备记录材料的前提。然而，为了将这些薄膜用作实际记录介质，必须克服几个问题，包括高温下的相稳定性。因此，本研究考察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。为了评价薄膜的性质，还测量了溅射薄膜的电阻率，并测量了薄膜的磁性能(即VSM曲线)。主要研究结果如下：(1)通过控制氮气和氩气的比例、衬底温度、放电电压和放电电流，可以制备出各种氮化铁薄膜。研究还发现，在较高的衬底温度下制备的薄膜呈现出非常尖锐的X射线峰，并由STAB…组成(2)用原位电子显微镜观察了沉积的氮化铁薄膜在加热过程中的结构变化：溅射的薄膜含有少量的α相作为局部分布的细小颗粒。随着温度的升高，氮原子和铁原子都开始发生位置有序化，在加热过程中得到了完全有序的Fe3N相。在不同的升温速率下，观察到了从epsilon相到伽马‘相的两种结构变化：根据氮原子和铁原子的扩散和剪切位移，很好地解释了这些特征。考虑到加热过程中发生的相分离和析出，较好地解释了不同热处理后的VSM曲线特征。对不同类型的镀铁膜进行了镀态薄膜的电阻率测量。结果表明，在较高的溅射气压下制备的薄膜具有较高的电阻率。考虑到沉积时薄膜中形成的晶界周围发生了质的变化，这一点得到了很好的解释。电学测量是评价薄膜性能的一种有效方法。进一步的详细研究正在进行中。较少

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