Deposition temperature mediated tunable tilt angle magnetization in Co–Pt/Ni 81 Fe 19 exchange springs

In this study, we investigate the effect of deposition temperature of Co–Pt fixed layer, Td,CoPt (150, 250and 350°C) on the tilt angle magnetization (θM) of Ni81Fe19-layer grown at room temperature (RT) and at different thicknesses (tNiFe=0, 1.0, 2.5 and 4.0nm) in Co–Pt(Td,CoPt)/NiFe(tNiFe) exchange springs. The magnetic studies demonstrated a strong perpendicular magnetic anisotropy (PMA) for the equi-compositional ordered Co–Pt layer grown on glass substrate using the film sequence: Ta(20nm)/Pt(20nm)/CoPt(5nm), regardless of Td,CoPt. The PMA can be retained with the addition of a 4-nm NiFe layer on the top when Td,CoPt≥250°C. In contrast, relatively a thin layer of Ni–Fe (2.5nm) can destroy the perpendicular exchange-spring behavior if the Co–Pt layer is deposited at RT. Using 3-D micromagnetic simulation, the interfacial exchange coupling strength (Aij) between the Co–Pt and NiFe-layers was estimated and the Aij value is found to increase rapidly when Td,CoPt is increased from RT to 300°C. Besides, the magnetization tilted angle (θM) of NiFe can be easily tuned from completely out-of-plane to almost 60° when tNiFe=4.0nm. Through this study, it is demonstrated that the θM of NiFe-layer can be tuned by not only altering the tNiFe; but also by varying the Td,CoPt.