I. Introduction
Perpendicular magnetic recording has been studied for more than 20 years [1] and announced to come onto the hard disk drive (HDD) market by the middle of this year. In perpendicular recording medium, a Co-Pt-Cr-SiO granular film has been studied for the application [2]. This material forms a very distinct segregated structure which consists of very fine crystal grains of Co-Pt-Cr with relatively large magnetic anisotropy constant surrounded by grain boundaries of SiO . However, a larger magnetic anisotropy is required for obtaining a higher recording density toward 1 Tbit/in with sufficient thermal stability. A large is also needed for reducing required perpendicular coercivity, , [3], so as to keep thermal stability and a large output signal.