鐵白金薄膜其應力誘導異常晶粒成長與(001)優選方位關係之研究

Abstract

Abstract Due to the remarkable intrinsic properties of L10 FePt including high magnetocrystalline anisotropy (Ku~7×107erg/cm3), high Curie temperature and etc, it has the potential of being the material for the next generation ultrahigh density media. However, as the FePt thin film deposited under room-temperature (RT) is disordered, in order to get industry required magnetically hard property, annealing process is essential for phase transformation as well as monitoring its (001) preferred orientation and magnetism quality. There are many previous studies on FePt texture evolution, but no prior research had been done using microstructure study. In this experiment, by using TEM imagery, we can understand the mechanism of texture evolution more clearly than before. In this experiment, we fabricated FePt thin film at room temperature. There are four parameters of thickness, including 10 nm, 20 nm, 30 nm and 40 nm. Annealing temperature increase from 450 oC to 800 oC, and each 50 oC is set as a parameter. Then we compared them to the controlled room temperature sample by focusing on analyzing the Residual strain, magnetism, crystallographic structure and microstructure. Sorder and LOF are measured through crystallographic structure where Residual strain by X-ray at NSRRC. The grain size first decreased from 12.0 nm to 8.5 nm which was caused by phase transformation occurred at annealing temperature of 500 oC. From 550 oC to 600 oC , (001)grains and (111)grains growth occurs simultaneously and grain size increased to 16.0 nm due to the coexistence of strain-induced and surface-energy-induced conditions. When grain growth meet certain condition changes as temperature rises from 600 oC to 650 oC, new (001)grains generate, (111)grains dissolve and grain size decrease from 16.0 nm to 7.5 nm. In the end, this phenomenon caused the sample to have grains of (001) preferred orientation, and showed that stress induce (001)grains growth had occurred. We also obtained a good magnetism for ultrahigh density recording media. By experimenting on different thicknesses of FePt film and focusing on analysing residual stress, magnetism and macrostructure. We found that we’ll get less (001) preferred orientation and magnetism in thicker thin film. The initial strain of 10 nm FePt is 0.7% tensile strain; where 40 nm FePt is -0.18% compressive strain. The tensile stress significantly helped compressive strain that is caused by phase transformation to release, which can positively affect the results of LOF and magnetism. From the strain figure, we found post-ordered 10 nm FePt thin film strain increased faster than 40 nm ones. This fast increase provided stronger source for (001)grains growth and (111)grains sufficient time to dissolve. which created good magnetism and (001) preferred orientation in thinner films, thus conveniently provided special magnetism feature for industrial engineering.