Optimization of Skyrmionic Magnetic Tunnel Junctions

Magnetic skyrmions are recognized as potential information carriers for building the next-generation spintronic memory and logic devices. Towards functional device applications, efficient electrical detection of skyrmions at room temperature is one of the most important prerequisites. Magnetic tunnel junctions (MTJs) offer a technologically feasible solution by using spin-dependent tunneling of electrons, which can output the presence and absence of skyrmion as the pronounced tunneling magnetoresistance (TMR). However, a successful integration of skyrmionic films with MTJ stacks, together with the subsequent electrical detection of mobile skyrmions, is limited by several important factors, which will be systematically addressed in this study. In particular, we will show our optimization strategy of integrating the multilayer [Pt/Co/Ta]₁₀ that hosts room temperature skyrmions, with the Ta(spacer)/CoFeB₁/MgO/CoFeB₂ MTJ stack that exhibits a perpendicular magnetic anisotropy (PMA). By changing the thickness of the Ta spacer, we establish a ferromagnetic coupling between the [Pt/Co/Ta]₁₀ multilayer and the bottom CoFeB₁ free layer, which is critical for imprinting room-temperature skyrmions from the [Pt/Co/Ta]₁₀ multilayer into the free layer of the MTJ stack. The skyrmionic MTJ stack is further optimized by changing both the thickness of the bottom CoFeB₁ layer and the annealing temperature. As a result, a TMR ratio of 100% and the electrical signature of the skyrmion phase are successfully obtained at room temperature. Our optimization strategy of the skyrmionic MTJ stack and enhanced performance of skyrmionic MTJ devices could accelerate the exploration of skyrmionic memory and logic devices.