Isolation of grains in Co-Pt films sputter-deposited by using a wet etching process

A Co-Pt film treated by using a wet etching process with a 7 % nitric acid solution exhibited a very high out-of-plane coercivity of up to 7046 Oe, which is two times higher than that of the as-deposited film. The scanning electron microscopy (SEM) images showed that the grain boundaries of the wet etched Co-Pt film appeared to be more vacant than those of the as-deposited film. The grain boundaries are thought to be preferentially etched because the energy of the grain boundaries is higher than that of the grains. According to the magnetic force microscope (MFM) results, the magnetic domain size of the wet etched film is clearly reduced compared with that of the as-deposited film. These results indicate that the wet etched Co-Pt films exhibit weaker exchange coupling and enhanced out-of-plane coercivity, which will give rise to a medium noise reduction.