Second-harmonic signature of chiral spin structures in W/Pt/Co heterostructures with tunable magnetic anisotropy

Second-harmonic Hall voltage (SHV) measurement method has been widely used to characterize the strengths of spin-orbit torques (SOTs) in heavy metal/ferromagnet thin films saturated in the single-domain regime. Here, we show that the magnetic anisotropy of a W/Pt/Co trilayer can be robustly tuned from in-plane to out-of-plane by varying W, Pt, or Co thicknesses. Moreover, in samples with easy-cone anisotropy, SHV measurements exhibit anomalous 'humps' in the multidomain regime accessed by applying a nearly out-of-plane external magnetic field. These hump features can only be explained as a result of the formation of Neel-type domain walls, efficiently driven by nevertheless small SOTs in this double heavy metal heterostructure with canceling spin Hall angles.