Authors: Long Liu, Yuhang Song, Xiaotian Zhao, Wei Liu, Zhidong Zhang
Published: 2022-07-19
Source: Full article
AbstractCurrent‐induced magnetization switching without the assistance of an in‐plane magnetic field by using the spin orbit torque (SOT) has attracted lots of attention for the novel energy‐efficient and nonvolatile spintronics devices. In this study, a full‐scale field‐free SOT switching in perpendicularly magnetized Ru/Pt/HoCo/Ru multilayers with a designed vertical composition gradient is reported. Through annealing the multilayers at 150 °C for 0–40 min, a structural change from a multilayer to an alloying structure with mixed distribution of Ho and Co is found. Simultaneously, the field‐free switching gradually turns from a full‐scale to a partial switching with the structural change. The multiple mechanisms brought by fabricating the HoCo layers with vertical composition gradient (including the non‐uniform Dzyaloshinskii–Moriya interaction (DMI), the defects, the inevitable lateral gradient, or the exchange bias effect along the thickness direction) lead to the deterministic field‐free switching. In addition, a detailed study on the stack of Ru/gradient HoCo/Ru shows that HoCo itself can also produce a certain amount of SOT to realize a partial switching in the absence of the in‐plane field. This work provides a route via engineering rare‐earth‐transition‐metal ferrimagnet to manipulate DMI and SOT for fully electrically controlled spintronics devices.