Room-temperature spin-orbit torque in an epitaxial half-Heusler alloy NiMnSb single layer on an MgO(100) substrate

Inversion symmetry breaking plays a pivotal role in various quantum phenomena and is fundamental for the generation of spin-orbit torque (SOT), which is essential for the advancement of next-generation spintronic technologies. By use of a ferromagnetic single layer exhibiting crystal inversion asymmetry, the efficiency of SOT magnetization switching has been significantly increased at low temperatures. To extend its applicability to room temperature, we engineered an epitaxial ferromagnetic half-Heusler alloy $\mathrm{Ni}\mathrm{Mn}\mathrm{Sb}$ single layer with an intrinsic bulk noncentrosymmetric structure on an $\mathrm{Mg}\mathrm{O}$(100) substrate using magnetron sputtering. Through a comprehensive analysis of the angular correlation of the planar Hall resistance ${R}_{\mathrm{PH}}$, the SOT efficiency was found to be 16.8 Oe/(${10}^{6}\phantom{\rule{0.2em}{0ex}}\mathrm{A}/{\mathrm{cm}}^{2}$), which significantly exceeds that of conventional heavy metal/ferromagnet bilayer structures and a $\mathrm{Ni}\mathrm{Mn}\mathrm{Sb}$ single layer grown on $\mathrm{Ga}\mathrm{As}$ substrates. The high efficiency can be attributed to the intrinsic crystallographic symmetry breaking and half-metallic properties of $\mathrm{Ni}\mathrm{Mn}\mathrm{Sb}$, and the extremely small lattice mismatch (0.15%) with $\mathrm{Mg}\mathrm{O}$. Our results provide compelling experimental evidence advocating the use of a $\mathrm{Ni}\mathrm{Mn}\mathrm{Sb}$ single layer in practical SOT-based devices, advancing the development of high-performance, energy-efficient spintronic applications.