Abstract：We investigate the spin Hall magnetoresistance (SMR) in all-antiferromagnetic heterostructures $\alpha$-Fe$_{2}$O$_{3}$/Cr$_{2}$O$_{3}$ with Pt contacts. When the temperature is ultralow ($ < $ 50 K), the spin current generated in the Pt layer cannot be transmitted through Cr$_{2}$O$_{3}$ ($t = 4$ nm), and the SMR is near zero. Meanwhile, when the temperature is higher than the spin fluctuation temperature $T_{\rm F}$ ($\approx $ 50 K) of Cr$_{2}$O$_{3}$ and lower than its Néel temperature $T_{\rm N}$ ($\approx $ 300 K), the spin current goes through the Cr$_{2}$O$_{3}$ layer and is reflected at the $\alpha$-Fe$_{2}$O$_{3}$/Cr$_{2}$O$_{3}$ interface; an antiferromagnetic (negative) SMR is observed. As temperature increases higher than $T_{\rm N}$, paramagnetic (positive) SMR mainly arises from the spin current reflection at the Cr$_{2}$O$_{3}$/Pt interface. The transition temperatures from negative to positive SMR are enhanced with increasing Cr$_{2}$O$_{3}$ layer thickness, accompanied by the absence of SMR signals when $t = 10$ nm. Such a tunable SMR builds a bridge between spin transport and structures. It also enriches antiferromagnetic spintronics.
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2022, Vol. 39 
