Effective manipulation of multi-state memory in bulk PtCo/IrMn via spin-orbit torque.

The development of exchange bias multi-state devices requires further reduction of the critical spin-orbit torque (SOT) switching current and increased anomalous Hall resistance. Compared to conventional PtCo bilayer/IrMn stacks, the bulk PtCo/IrMn system offers comparable switching energy efficiency with a larger readout signal amplitude arising from its enhanced anomalous Hall resistance. Multiple exchange bias states can be reversibly programmed through SOT, providing a viable pathway for multi-bit storage and analog state representation. Moreover, the observed improvement in damping-like SOT efficiency is attributed to the graded Pt distribution, confirming the advantage of the multilayer design in enhancing current-to-spin conversion. Together, these characteristics make bulk PtCo/IrMn a promising platform for next-generation spintronic memory and spin logic devices applications.