Interplay between out-of-plane anisotropic L1₁-type CoPt and in-plane anisotropic NiFe layers in CoPt/NiFe exchange springs

Films of L1₁-type CoPt/NiFe exchange springs were grown with different NiFe (Permalloy) layer thickness (t_NiFe = 0-10 nm). X-ray diffraction analysis reveals that the characteristic peak position of NiFe(111) is not affected by the CoPt-layer - confirming the absence of any inter-diffusion between the CoPt and NiFe layers. Magnetic studies indicate that the magnetization orientation of NiFe layer can be tuned through varying t _NiFe and the perpendicular magnetic anisotropy of L1₁-type CoPt/NiFe films cannot sustain for t_NiFe larger than 3.0 nm due to the existence of exchange interaction at the interface of L1₁-CoPt and NiFe layers. Magnetic force microscopy analysis on the as-grown samples shows the changes in morphology from maze-like domains with good contrast to hazy domains when t_NiFe-≥ 3.0 nm. The three-dimensional micro-magnetic simulation results demonstrate that the magnetization orientation in NiFe layer is not uniform, which continuously increases from the interface to the top of NiFe layer. Furthermore, the tilt angle of the topmost NiFe layers can be changed over a very wide range from a small number to about 75°by varying t_NiFe from 1 to 10 nm. It is worth noting that there is an abrupt change in the magnetization direction at the interface, for all the t_NiFe investigated. The results of present study demonstrate that the tunable tilted exchange springs can be realized with L1₁-type CoPt/NiFe bilayers for future applications in three-axis magnetic sensors or advanced spintronic devices demanding inclined magnetic anisotropy.