Abstract
Media trilemma has been the barrier for increasing the recording density of HDD for years. To break through the media trilemma in HDD, the ideal of granular L10 FePt for energy assisting magnetic recording was proposed and several requirements for granular L10 FePt must be achieved such as large perpendicular coercivity (>1.8T), small granular size, FePt (001) prefer orientation, narrow grain size distribution, narrow switch field distribution and columnar growth. Among all segregants, the grain size of FePt:B presented the smallest grain size and the surface energy of boron (~2.3kJ/m2) is the closet to it of FePt (~2.5kJ/m2) which means the potential to promote columnar growth. We first fabricated granular FePt:B and studied the effect of adding boron into FePt. It was found that boron would significantly hinder FePt order-disorder transition and thus contributed a rather low perpendicular coercivity. To solve this problem, the post-annealing processes were carried out to promote FePt order-disorder transition and the behavior of boron during FePt order-disorder transition was studied. However it turned out to be a dilemma between granular structure and magneto-crystalline anisotropy. According to recent work, carbon was considered to be the one that would not hinder the FePt order-disorder transition heavily nor degrade the crystalline of FePt (001) and (002). Therefore, the coercivity of granular L10 FePt:C was higher than it in other segregants. The ideal of multi-segregant of granular FePt:B,C was then proposed to take the advantages of both boron and carbon. We first fabricated granular L10 FePt:C as an ordered seed layer and then capping boron onto FePt:C. By post annealing, we successfully demonstrated multi-segregant of granular FePt:B,C.