Abstract
Current-induced spin-orbit torques (SOTs) are of interest for fast and energy-efficient manipulation of magnetic order in spintronic devices. To be deterministic, however, switching of perpendicularly magnetized materials by SOT requires a mechanism for in-plane symmetry breaking. Existing methods to do so involve the application of an in-plane bias magnetic field, or incorporation of in-plane structural asymmetry in the device, both of which can be difficult to implement in practical applications. Here, we report bias-field-free SOT switching in a single perpendicular CoTb layer with an engineered vertical composition gradient. The vertical structural inversion asymmetry induces strong intrinsic SOTs and a gradient-driven Dzyaloshinskii–Moriya interaction (g-DMI), which breaks the in-plane symmetry during the switching process. Micromagnetic simulations are in agreement with experimental results, and elucidate the role of g-DMI in the deterministic switching processes. This bias-field-free switching scheme for perpendicular ferrimagnets with g-DMI provides a strategy for efficient and compact SOT device design.
Highlights
Current-induced spin-orbit torques (SOTs) are of interest for fast and energy-efficient manipulation of magnetic order in spintronic devices
For memory applications where information is encoded in the direction of the magnetization in magnets with perpendicular magnetic anisotropy (PMA), Spin-orbit torque (SOT) switching is realized in a non-magnet/ferromagnet (NM/FM) or NM/FIM heterostructure with the assistance of an external in-plane magnetic field Hex along the current direction[1,2,10,11,12]
CoTb was constructed by a co-sputtering process of Co and Tb at different powers to control the stoichiometry of the final CoTb layer
Summary
Current-induced spin-orbit torques (SOTs) are of interest for fast and energy-efficient manipulation of magnetic order in spintronic devices. Mechanisms to break the in-plane (structural or magnetic) symmetry, instead of Hex, are being investigated to realize practical SOT memory devices[13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28] To date, these have included inplane exchange bias fields[14,15,16], interlayer exchange coupling[17,18], in-plane structural, composition, or interfacial oxidation asymmetry[19,20,21,22,23,24,25], and combining multiple competing sources of spin torque in one device[26,27,28]. Instead, that a structure featuring in-plane symmetry, along with inversion asymmetry only along the growth direction, can exhibit deterministic switching due to the dynamic in-plane breaking of symmetry during the switching process, induced by the Dzyaloshinskii–Moriya interaction (DMI)
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