Unconventional unidirectional magnetoresistance in heterostructures of a topological semimetal and a ferromagnet

Unidirectional magnetoresistance (UMR) in a bilayer heterostructure, consisting of a spin-source material and a magnetic layer, refers to a change in the longitudinal resistance on the reversal of magnetization and originates from the interaction of non-equilibrium spin accumulation and magnetization at the interface. Since the spin polarization of an electric-field-induced non-equilibrium spin accumulation in conventional spin-source materials is restricted to be in the film plane, the ensuing UMR can only respond to the in-plane component of magnetization. However, magnets with perpendicular magnetic anisotropy are highly desired for magnetic memory and spin-logic devices, whereas the electrical read-out of perpendicular magnetic anisotropy magnets through UMR is critically missing. Here we report the discovery of an unconventional UMR in the heterostructures of a topological semimetal (WTe₂) and a perpendicular magnetic anisotropy ferromagnetic insulator (Cr₂Ge₂Te₆), which allows to electrically read the up and down magnetic states of the Cr₂Ge₂Te₆ layer through longitudinal resistance measurements.