All-Linear Multistate Magnetic Switching Induced by Electrical Current

We present an alternative mechanism to control domain wall motion, whose directions are manipulated by the amplitude of electrical current rather than its sign when modulating the exchange stiffness A while maintaining the Dzyaloshinskii-Moriya interaction constant D. To confirm this mechanism, we observe this type of domain wall motion and demonstrate linear magnetic switching without hysteresis effect via adjusting A of a $\mathrm{Ta}/\mathrm{Pt}/\mathrm{Co}/\mathrm{Ta}$ multilayer device with ion implantations. We further find field-free biased and chirally controllable multistate switching at the lateral interface of ion exposed and unexposed areas, which is due to current-induced N\'eel wall motion and a strong exchange coupling at this interface.