We report on efficient spin current generation at room temperature in rutile
type WO2โ grown on Al2โO3โ(0001) substrate. The optimal WO2โ
film has (010)-oriented monoclinically distorted rutile structure with metallic
conductivity due to 5d2 electrons, as characterized by x-ray
diffraction, electronic transport, and x-ray photoelectron spectroscopy. By
conducting harmonic Hall measurement in Ni81โFe19โ/WO2โ bilayer, we
estimate two symmetries of the spin-orbit torque (SOT), i.e., dampinglike (DL)
and fieldlike ones to find that the former is larger than the latter. By
comparison with the Ni81โFe19โ/W control sample, the observed DL SOT
efficiency ฮพDLโ of WO2โ (+0.174) is about two thirds of that of W
(-0.281) in magnitude, with a striking difference in their signs. The magnitude
of the ฮพDLโ of WO2โ exhibits comparable value to those of widely
reported Pt and Ta, and Ir oxide IrO2โ. The positive sign of the
ฮพDLโ of WO2โ can be explained by the preceding theoretical study
based on the 4d oxides. These results highlight that the epitaxial
WO2โ offers a great opportunity of rutile oxides with spintronic
functionalities, leading to future spin-orbit torque-controlled devices.Comment: 14 pages, 4 figure