Role of Ta-spacer layer on tuning the tilt angle magnetic anisotropy of L11-CoPt/Ta/NiFe exchange springs

Abstract

L11-CoPt/Ta/NiFe trilayers are chosen as model films for probing the role of spacer layer on tuning the tilt angle magnetization (θM) in such exchange springs. For this purpose, a non-magnetic layer (Ta) with varying thickness (tTa) from 0 to 2.5nm was inserted between 10-nm thick CoPt film exhibiting strong perpendicular magnetic anisotropy (PMA) and 4-nm thick NiFe film having in-plane magnetic anisotropy (IMA). With the insertion of Ta-spacer, the magnetic hysteresis loops become more and more tilted as tTa increases. Upon increasing the tTa from 0 to 2.5nm, the estimated SQR⊥ (=Mr⊥/Ms⊥) from the M–H loops is found to decrease moderately; while the θM increases significantly from 43° to 77°. MFM images revealed maze-like domain patterns and the domain size tends to increase at the expense of magnetic phase contrast with increasing tTa. Micro-magnetic simulation of tilt in the anisotropy axis with respect to the bare CoPt-layer showed a trend similar to that of those observed with the M–H loops obtained by VSM measurements. The results of present study suggest that the insertion of Ta-spacer is not only beneficial in terms of preserving the competing anisotropies such as PMA and IMA of CoPt and NiFe-layers respectively through weakened exchange coupling; but also, act as an appropriate means for realizing tunable tilted magnetic anisotropy in the L11-CoPt/NiFe exchange springs.