Low damage smoothing of magnetic materials using off-normal gas cluster ion beam irradiation

A damage-free smoothing process for magnetic materials using a gas cluster ion beam (GCIB) has been studied. As the areal density of hard disk drives (HDDs) has increased, the flying height of the magnetic recording head above the disk has been decreasing. In order to further reduce the flying height and improve the sensitivity of sensors, a damage-free smoothing technology for magnetic materials is imperative. A GCIB process has been proposed as a novel smoothing technique for various materials. With this process it is expected that the damage will be low, since the gas clusters are aggregations of a few to thousands of atoms or molecules. In this paper, oblique GCIB irradiation has been studied in order to achieve low damage smoothing of PtMn and NiFe thin films. The surface morphology after GCIB irradiation was observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). A smooth surface with an average roughness of less than 1 nm was obtained by using oblique GCIB irradiation. Irradiation damage, such as fluctuations in the ratio of the material components and oxidation of the surface, were investigated by secondary ion mass spectrometry (SIMS). The fluctuations were suppressed by using oblique GCIB irradiation with incident angles larger than 80°. Consequently, irradiation from a GCIB at grazing incidence can be applied to achieve low-damage smoothing of magnetic materials.