Field‐Free Switching In article number 2211953, Tiejun Zhou, Wenjun Li, and co‐workers report that field‐free switching and high spin‐orbit torque efficiency are simultaneously achieved through the introduction of exchange field gradient into perpendicularly magnetized synthetic ferro‐ and antiferromagnets. The study provides new insights into field‐free switching of synthetic antiferromagnets and paves the way for memory and logical applications.

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Ir-CoFeB-based synthetic antiferromagnets (SAFs) are potential candidates as the free layer of the next-generation magnetic tunnel junctions (MTJs) for high speed and density memories due to their perpendicular magnetic anisotropy and strong interlayer exchange coupling. However, the field-free spin–orbit torque (SOT) switching of Ir-CoFeB-based SAFs has rarely been reported, especially in the Co/Ir/CoFeB system with high anti-interference capability and being readily integrated with MTJs. In this paper, SOT-induced magnetization switching and SOT efficiency in Co/Ir/CoFeB SAFs with perpendicular anisotropy and tunable exchange coupling are systemically investigated. A full field-free switching of perpendicular Co/Ir/CoFeB SAFs is realized by depositing them onto crystal miscut Al2O3 substrates, which induce a tilted magnetic anisotropy. Furthermore, by introducing crystalline MgO or amorphous HfO2/SiO2 as the seed layers, the source of the tilted magnetic anisotropy was proved to be from the transverse asymmetry caused by the crystal miscut. Moreover, the crystal miscut enhances the SOT efficiency. The findings provide an approach to reliable field-free switching and high SOT efficiency of Ir-CoFeB-based SAFs for memories as well as logics with low power, fast speed, and high density.

Spin–orbit torque (SOT) is an emerging candidate for electrically controlled magnetization switching in low-power and nonvolatile spintronic devices. However, SOT switching of perpendicular magnetization requires an auxiliary field or additional lateral symmetry breaking, which is difficult to achieve in practical applications. In particular, the mechanism of field-free switching through vertical symmetry breaking still lacks a quantitative description. In this work, a vertically asymmetric Co/Pt bilayer has been constructed through quantitative engineering of anisotropy gradient, while keeping the total magnetic thickness of the bilayer constant. Interestingly, the enhanced asymmetry with greater anisotropy gradient would induce higher SOT efficiencies and larger field-free switching ratios. Field-free switching can be attributed to the slight lateral asymmetry caused by the perpendicular anisotropy gradient. The SOT effective-field enhancement and field-free switching through quantitative engineering of the anisotropy gradient not only offer a deeper understanding of current-induced magnetization switching in perpendicularly asymmetric systems but also provide a potential avenue for practical applications of SOT devices at the wafer level.