Field-free SOT switching in Pd/PdCo bilayers with a vertical gradient induced by rapid thermal annealing

Achieving field-free magnetization switching in spin–orbit torque (SOT) devices is essential for practical spintronic applications. While recent studies have proposed strategies involving complex multilayer structures or substrate symmetry engineering, which often necessitates high substrate temperatures during deposition, thereby limiting large-scale integration. Here, we demonstrate a simple and complementary metal–oxide–semiconductor (CMOS)-compatible approach to achieve current-induced field-free SOT switching in Pd/PdCo bilayers deposited at room temperature and subsequently processed via rapid thermal annealing (RTA). We show that field-free SOT switching is robust across different substrates (Al2O3 and SiO2/Si) and is independent of the in-plane crystalline symmetry associated with the substrates. Systematic investigations reveal that the RTA-induced vertical composition gradient, coupled with gradient-induced Dzyaloshinskii–Moriya interaction, enables the observed field-free switching of magnetization. Furthermore, we clarify how annealing temperature, Co/Pd ratio, and Pd/PdCo bilayer stacking configuration influence the switching behavior. Our study establishes a viable strategy for field-free SOT switching with great CMOS compatibility, offering a promising path toward energy-efficient spintronic devices.