R&D: Tailoring Microstructure and Formation of Hexagonal-Bn Segregants in Fept-Based Granular Films for Improved HAMR Media

SSRN has published an article written by D. Ogawa, National Institute for Materials Science, 1-2-1, Tsukuba, 305-0047, Ibaraki, Japan, Yukiko Takahashi, and Hossein Sepehri-Amin, National Institute for Materials Science – Elements Strategy Initiative Center for Magnetic Materials (ESICMM), National Institute for Materials Science, 1-2-1, Tsukuba, 305-0047, Ibaraki, Japan.

Abstract: “Reducing the grain size to the level of 5nm while maintaining high coercivity in FePt granular media is essential to increase the areal density of heat assisted magnetic recording (HAMR) media to 4 Tb/in2. In this work, we demonstrate how the formation of hexagonal BN (ℎ-BN) intergranular phase can benefit this goal by optimizing the processing conditions of film development, such as the introduction of nitrogen (N2) gas and RF bias during the deposition of FePt-BN granular films. It was found that the control of the N2 gas flow is an effective way to transfer amorphous BN as an intergranular phase to hexagonal BN, resulting in a reduction of the mean and standard deviation of the FePt grain and an increase in the grain density. X-ray photoelectron spectroscopy (XPS) analysis suggests that the use of RF bias and N2 gas during sputtering of FePt-BN increases the sp2 BN bonding, and promotes the formation of ℎ-BN in the intergranular phase region. However, it was observed that excess nitrogen can have a negative effect on the L10 ordering and coercivity that can originate from interdiffusion of N or B into FePt grains. A notable achievement by this process is the improved microstructure and magnetic properties in FePt-BN granular films, which will have a significant impact on increasing the areal density of HAMR media.“