Abstract
The origin of spin–orbit torques, which are generated by the conversion of charge-to-spin currents in non-magnetic materials, is of considerable debate. One of the most interesting materials is tungsten, for which large spin–orbit torques have been found in thin films that are stabilized in the A15 (β-phase) structure. Here we report large spin Hall angles of up to approximately –0.5 by incorporating oxygen into tungsten. While the incorporation of oxygen into the tungsten films leads to significant changes in their microstructure and electrical resistivity, the large spin Hall angles measured are found to be remarkably insensitive to the oxygen-doping level (12–44%). The invariance of the spin Hall angle for higher oxygen concentrations with the bulk properties of the films suggests that the spin–orbit torques in this system may originate dominantly from the interface rather than from the interior of the films.
Highlights
The origin of spin–orbit torques, which are generated by the conversion of charge-to-spin currents in non-magnetic materials, is of considerable debate
Our materials’ characterization shows that the incorporation of oxygen stabilizes the b À W. This is consistent with previous studies, which have shown that the formation of b À W is extremely sensitive to the oxygen incorporation during the growth process[37,38,39,40,41], and an oxygen concentration of only 10% is sufficient to stabilize b À W
Despite the large changes we have observed in the bulk microstructure, and a resistivity change by a factor of 2, we see that the spin Hall angle (SHA) still remains very large
Summary
The origin of spin–orbit torques, which are generated by the conversion of charge-to-spin currents in non-magnetic materials, is of considerable debate. We report large spin Hall angles of up to approximately –0.5 by incorporating oxygen into tungsten. While the incorporation of oxygen into the tungsten films leads to significant changes in their microstructure and electrical resistivity, the large spin Hall angles measured are found to be remarkably insensitive to the oxygen-doping level (12–44%). One of the most efficient materials exhibiting spin–orbit torques is the highly resistive b-phase of tungsten, where SHAs of up to approximately À 0.35 have been reported[24,25,26]. We demonstrate that by doping oxygen into tungsten thin films, large spin–orbit torques are attained that are rather insensitive to considerable changes in the resistivity and film microstructure. Our findings suggest that these very-efficient spin–orbit torques are largely interfacial in origin
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