Observation of uniaxial magnetic anisotropy and out-of-plane coercivity in W/Co20Fe60B20/W structures with high thermal stability

In this study, the development of uniaxial magnetic anisotropy (UMA) and out-of-plane coercivity (Hc┴) in W/Co20Fe60B20(CoFeB)/W structures by tuning the annealing temperature (TA) such as 300°C, 400°C and 500°C were achieved. For 400°C film, W and CoFeB interfaces play a major role in achieving the large Hc┴. Furthermore, the observation of large Hc┴ was found to be significantly induced by the interface on the two sides of CoFeB layer. The two-fold UMA strongly is stabilized in W/CoFeB/W trilayers up to 500°C. A maximum in-plane uniaxial anisotropy energy density (Ku) was observed for the 500°C annealed films, which is accompanied by the dominance of Hc┴ owing to the over-oxidation and/or occurrence of inter-diffusion across the interfaces. The oxidation and relieving of boron atoms in the CoFeB at higher annealing temperatures were confirmed by X-ray photoelectron spectroscopy (XPS). The control over the interface shared between the W and CoFeB is concluded to be essential in order to alter the strength of magnetic anisotropy. Hence, an investigation on W/CoFeB/W structures could be very beneficial for the modern Spin-Orbit Torque (SOT) based data storage applications and this inspires relevant research work to widen magnetic systems.