Tailoring Magnetic Skyrmion Dimensions via Precise Interface Roughness Modulation in W-Inserted Skyrmion SOT Channel Grown on β-Phase W Seed Layer

Abstract

For skyrmion-based perpendicular (p) Spin-Orbit-Torque (SOT) magnetic random-access-memory (MRAM), a tungsten (W)-inserted skyrmion SOT channel was designed by a precise modulation of the W insert layer thickness (tw,insert) having 0.100-0.142 nm as well as the interface roughness (Ra,interf,sky) having 18.13-33.73 pixel density (a.u.) between ferromagnet Co2Fe6B2 free layer and MgO tunneling barrier. An inverse relation was found between Ra,interf,sky and tw,insert; i.e., a higher Ra,interf,sky required a smaller tw,insert. In addition, Ra,interf,sky is critically determined by the surface roughness (Ra,surf,seed) of the beta-phase SOT seed layer having 0.120-0.138 nm. A higher Ra,surf,seed induced significantly a higher Ra,interf,sky. Particularly, a precise design of the skyrmion diameter (0.96-0.62 & micro;m) and density (0.093-0.140 ea/& micro;m2) found that a higher Ra,interf,sky led to a smaller skyrmion diameter and a higher skyrmion density. These results demonstrate a practical possibility of a skyrmion-based SOT MRAM via a new inserted material and its related precise modulation of Ra,interf,sky.