Efficient spin transmission of Ti spacer for magnetic heterostructures with perpendicular magnetic anisotropy

Abstract

Perpendicular magnetization switching induced by spin–orbit torque (SOT) in spin source metals/ferromagnetic material heterostructures is of fundamental interest for developing next-generation magnetic random-access memory with nonvolatility, high-density, and low-power consumption. Nonetheless, obtaining perpendicularly magnetized ferromagnetic layers based on spin source materials with non-5d heavy elements continues to pose a significant challenge. In this study, we grew the Ti/CoFeB/MgO heterostructure with high perpendicular magnetic anisotropy (PMA) and low spin–orbit coupling. Compared with traditional 5d heavy metals, lower Dzyaloshinskii–Moriya interaction (DMI) constants and at least two orders of magnitude lower SOT efficiency were observed in Ti/CoFeB/MgO heterostructures. In the heavy metals (Ta or Pt)/Ti/CoFeB/MgO heterostructure, the spin current generated by the heavy metal can effectively penetrate through the Ti spacer, while the SOT efficiency gradually decreases with increase in Ti thickness, which obeys the bulk spin diffusion model. The SOT efficiency of spin source (heavy metal)/Ti/CoFeB/MgO heterostructure remains almost unchanged by introducing thin Ti spacer when thickness is less than 2 nm, thereby demonstrating efficient spin transition through the Ti layer. Furthermore, the Ti spacer can weaken the DMI between the spin sources and the ferromagnetic layer, thereby reducing the in-plane assistance magnetic field and enabling a lower critical current density for SOT-induced deterministic magnetization switching. These results suggest that the Ti/CoFeB/MgO heterostructure with PMA holds promise as a potential candidate for the development of SOT-based spintronic devices.