Abstract

Second harmonic Hall voltage (SHV) method [1] has been widely used to measure spin-orbit torques (SOTs) in heavy metal/ferromagnet (HM/FM) bilayers. It is typically applied for the single domain regime while the signals in multi-domain regimes are almost always ignored due to the complication from domain structures. In this study, we analyze the SHV data taken in a magnetic multilayer made of W/Pt/Co/SiO2. First harmonic planar Hall effect (PHE) and anomalous Hall effect (AHE) measurements reveal weak in-plane anisotropy of the Co layer. At low temperatures, the PHE loops become asymmetric, which indicate sizable Dzyaloshinskii-Moriya interaction (DMI) at the Pt/Co interface due to inversion symmetry breaking and strong spin-orbit coupling [2]. Typical sheared hysteresis for labyrinth domains is observed in AHE measurements. Interestingly, the second harmonic Hall voltage loops show “humps” in the intermediate field range where DMI-induced topological Hall effect and magnetic bubbles are typically observed. We explain such enhancement in SHV as a result of chiral Néel wall formation and efficient SOT driven domain wall motion [3]. Our results demonstrate that second harmonic voltage measurement can be utilized to detect chiral spin structures in magnetic multilayers. **

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