Anisotropy-Graded FePt(001) Magnetic Films Obtained by Graded Working Pressures

We herein investigate the performance of L1₀-FePt(001) films consisting of magnetically anisotropic-graded FePt layers grown by gradient working pressure (P_w). The graded structures typically consist of 5 nm thick FePt hard layer followed by five sequential layers of 1 nm thick graded-FePt layers deposited with P_w of 30, 20, 10, 7, and 3 mtorr, respectively. The structural and magnetic properties of P_w-graded-FePt layers thus fabricated on glass substrates are compared with that of those grown at different deposition temperatures, T_d of 300 °C, 350 °C, 400 °C, and 450 °C. The FePt(P_w)-graded films exhibited a very high (001)-texture, island-like morphology, and strong perpendicular magnetic anisotropy and these performances are found to be consistent with that of the L1₀-FePt(001) hard layer. For T_d <; 400 °C, the FePt(P_w)-graded films not only showed remarkable declining trend for out-of-plane coercivity (H_c⊥) but also demonstrated single-phase magnetization reversal-suggesting the existence of strong exchange coupling between the hard and the graded layers. In contrast, at higher Td (≥400 °C) ledge or maze-type morphology with evidence of in-plane magnetic component is observed. Further, higher Td leads to the occurrence of intensive interlayer diffusion across the graded layers, which resulted in declining exchange-coupling behavior. The cross-sectional transmission electron microscopy images revealed epitaxial growth for the P_w-graded and the L1₀-FePt layers grown using MgO under layer. The results of this paper demonstrate the feasibility of obtaining magnetic gradation in the FePt(P_w)-graded films, satisfying the requirements of future magnetic recording with ultrahigh density.