Field-Free Reconfigurable Spin Logic in Compositionally Graded MnxCoAl Layer
Spintronic logic-in-memory provides a route to reducing data-transfer energy consumption and accelerating computation by integrating nonvolatile storage and logic functions within a single physical unit. Here, we investigate field-free spin-orbit-torque (SOT) switching and reconfigurable spin logic in a vertically composition-graded MnxCoAl/Pt heterostructure. In contrast to the uniform-composition Mn1.8CoAl/Pt and Mn2.5CoAl/Pt control devices, the Mn1.8-2.5CoAl gradient device exhibits deterministic SOT switching under zero external magnetic field. Dzyaloshinskii-Moriya interaction (DMI)-related measurements reveal a finite characteristic effective-field scale, indicating the involvement of chiral magnetization-reversal processes. Meanwhile, the vertical composition gradient introduces magnetic inhomogeneity that can modify domain nucleation and propagation, and the combined effects are consistent with the observed field-free switching behavior. The composition-gradient device further exhibits accumulative multistate switching with stable intermediate Hall-resistance states under zero magnetic field, whereas the uniform-composition controls do not show comparable stable multistate behavior. By tailoring the amplitude, polarity, and sequence of current pulses, the device can be tuned between binary and multilevel switching modes, enabling the experimental realization of AND, OR, NAND, and NOR Boolean operations within the same Hall-bar device without any external magnetic field. These results extend Mn-Co-Al Heusler heterostructures from field-assisted SOT switching toward field-free magnetization control, multistate operation, and reconfigurable spin logic through vertical composition engineering.