CrRu-X (X=VN, TiN, ZrN) seed layers effects on the epitaxial growth and magnetic properties of FePt-based films

Abstract

For heat-assisted magnetic recording media, each functional film, such as the underlayer/seed layer/heat-sink layer deposited on the amorphous soft magnetic underlayer/glass substrate, was required to grow epitaxially to promote the formation of (00L) textured FePt film. The Cr-based seed layer with (002)/[110] epitaxial orientation is essential for the growth of the MgO-based underlayer and the FePt perpendicular magnetic recording film. Here, the varied nitrides, VN, TiN, or ZrN, were further doped in the CrRu seed layer to modify the interface between the CrRu and MgTiON layer. For CrRu-X (X= TiN, ZrN) films, the Ti and Zr atoms were substituted in the CrRu lattice, which is evidenced in the lower diffraction angle (higher lattice constant) in the (002) plane, and the growth defects in the MgTiON layer can be improved due to smaller lattice misfit. In contrast, the lattice constant of CrRu-VN was close to the reference CrRu film because part of the VN was diffused up to the MgTiON layer and formed the bumpy morphology of grains, proved by the cross-sectional transition electron microscopy images and compositional analysis—the grain size and surface energy change when the VN presents around the MgTiON matric. The FePt (BN, Ag, C) film deposited on MgTiON/CrRu-VN shows the highest perpendicular magnetic anisotropy constant (K_u) with the value of 2.36 × 10⁶ J/m³, out of plane coercivity (H_c= 2013 kA/m) and lowest remanence ratio (0.187) which is the ratio between in-plane remanence and out-of-plane remanence from hysteresis loops. The nitride-doped CrRu-X seed layer affected the magnetic and microstructural of FePt (BN, Ag, C) film via diffused VN in the MgTiON lattice or minor lattice strain during thin film growth in MgTiON/CrRu-X (X= TiN, ZrN) system.