Peculiar spin Hall magnetoresistance in polycrystalline WTe2/Ni80Fe20 heterostructures

Charge–spin interconversion is a key issue in spintronics. It gives rise to a series of new phenomena, such as spin Hall magnetoresistance (SMR). In the present work, we report the peculiar SMR behaviors in heterostructures composed of polycrystalline WTe2 nanoplate and Ni80Fe20(Py) film. We observe a negative SMR, which is contrary to the positive SMR usually measured in heavy metal/ferromagnet bilayers. We further observe a transition from negative to positive SMR with increasing thickness of the WTe2 layer, as well as SMR sign reversal with increasing temperature in heterostructures with thicker WTe2. The peculiar SMR behaviors in polycrystalline WTe2/Py heterostructures are attributed to the interface-induced spin current and its competition with the spin Hall-induced spin current. The findings in this work offer a fundamental input for the future exploitation of heterostructures based on two-dimensional transition metal dichalcogenides.