Study on the domain structure and tunable spin orientation in L 1 1 -CoPt/NiFe exchange springs with Ta-spacer

In this study, we investigate the domain structure and tunable spin orientation in L11-CoPt(10nm)/NiFe(tNiFe) with insertion of 2-nm thick Ta-spacer and by varying NiFe-layer thickness, tNiFe =1.0, 2.5, 5.5, 7.0, 8.5 and 10nm. The L11-CoPt layer exhibits a strong perpendicular magnetic anisotropy and NiFe holds in-plane magnetic anisotropy and both were separated by the non-magnetic Ta-spacer. Upon increasing tNiFe, the magnetic hysteresis loops become more and more tilted along with moderate decrease in both H c⊥, and SQR⊥ values; while the estimated tilt angle magnetization (θ M) values tend to increase from 0 to 60°. Interestingly, with the insertion of Ta-spacer, significant enhancement in θ M (=45°) is achieved with tNiFe of ∼3nm in the CoPt/NiFe layers - indicating that increase in tNiFe induces tilting of CoPt spins even in the presence of Ta-spacer. Magnetic force microscopy studies on the the L11-CoPt/Ta/NiFe films revealed maze-like domain patterns and their magnetic phase contrasts tend to decrease with dominant topographic features upon increasing tNiFe. The results obtained with the micro-magnetic simulation on the tilt in anisotropy axis are found to be consistent with the experimental values of θ M