Field-free spin-orbit torque-induced switching of perpendicular magnetization in a ferrimagnetic layer with a vertical composition gradient

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.

Ferrimagnet GdFeCo Characterization for Spin‐Orbitronics: Large Field‐Like and Damping‐Like Torques

“…GdFeCo can thus generate efficient spin currents and the different symmetries allow this material to be used in a wide variety of devices for spintronics. For instance, the SHE spin current can generate self-torque [10] and can be used for the electrical switching of the magnetization, as shown in epitaxial FePt [44] or CoTb [45]. Also, the total spin current (SAHE+SHE) can be used to induce a torque on another magnetic layer or for the manipulation of skyrmions.…”

“…For instance, the SHE spin current can generate self‐torque [ 10 ] and can be used for the electrical switching of the magnetization, as shown in epitaxial FePt [ 44 ] or CoTb. [ 45 ] Also, the total spin current (SAHE + SHE) can be used to induce a torque on another magnetic layer or for the manipulation of skyrmions.…”

Field-free approaches for deterministic spin–orbit torque switching of the perpendicular magnet

“…In this case, the DMI determines the chirality of the SOT-induced spin textures along the thickness direction, and thus contributes to the deterministic SOT switching. It is worth noticing that the conventional interfacial DMI contribution is zero for the vertical spin textures, and the interlayer DMI plays the important role in this case, which has been discovered recently by the chiral interlayer exchange coupling phenomenon in multilayer systems [51][52][53][54][55][56].…”

Coming of the age with spintronics-based future information

“…例如 在Ta/CoFeB/TaO x 体系中, 利用楔形的TaO x 来调控Co-FeB垂直各向异性, 当楔形结构的梯度方向与电流方 向垂直时, 由于对称性破缺可以形成一个有效磁场实 现无外场调控 [13] . 另外, 在CoTb亚铁磁薄膜中沿垂直 方向上的成分梯度可以引入显著的本征SOT和Dzyaloshinskii-Moriya (DM)相互作用, 该DM相互作用可以 进一步打破面内的对称性从而使面外磁矩的无外场翻 转成为可能 [14] . 此外, 可以通过在多层膜结构中添加 反铁磁层, 或与铁磁层直接交换作用产生交换偏置场 作为垂直磁矩翻转的有效磁场 [15] .…”