Spin-Orbit Torque-Driven Field-Free Switching Of Perpendicular Magnetization In Ferromagnetic Layers With Vertical Composition Gradients

Abstract

The current-induced spin-orbit torques (SOTs) are fascinating because they allow the magnetic order in spintronic devices to be changed quickly and efficiently. However, a way to disrupt the symmetry in the material's plane is needed to guarantee that the transition of perpendicularly magnetic materials through SOT can be anticipate. Modern approaches to this problem include increasing the device's in-plane bias magnetic field strength or altering its design to be less uniform throughout the device's axis of rotation. Both of these plans, however, might be difficult to implement. In this case, we show how SOT switching works in a single, straight CoTb layer with a vertical composition gradient built without the bias element. During the switching phase, the in-plane symmetry is disrupted by a gradient-driven Dzyaloshinskii-Moriya interaction (g-DMI) and substantial intrinsic SOTs caused by the vertical structural inversion asymmetry. Experimental results are confirmed by micromagnetic models that explain the connection between g-DMI and deterministic switching to carry out. Using the bias-field-free switching strategy, g-DMI allows us to fabricate small, functional SOT devices for perpendicular ferrimagnets.