Browsing by Author "Wang, Yang"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
Item Observation of nonlinear planar Hall effect in magnetic-insulator–topological-insulator heterostructures(Physical Review B, 2022-10-10) Wang, Yang; Mambakkam, Sivakumar V.; Huang, Yue-Xin; Wang, Yong; Ji, Yi; Xiao, Cong; Yang, Shengyuan A.; Law, Stephanie A.; Xiao, John Q.Interfacing topological insulators (TIs) with magnetic insulators (MIs) have been widely used to study the interaction between topological surface states and magnetism. Previous transport studies typically interpret the suppression of weak antilocalization or appearance of the anomalous Hall effect as signatures of the magnetic proximity effect (MPE) imposed to TIs. Here, we report the observation of the nonlinear planar Hall effect (NPHE) in Bi2Se3 films grown on MI thulium and yttrium-iron-garnet (TmIG and YIG) substrates, which is an order of magnitude larger than that in Bi2Se3 grown on nonmagnetic gadolinium-gallium-garnet (GGG) substrate. The nonlinear Hall resistance in TmIG/Bi2Se3 depends linearly on the external magnetic field, while that in YIG/Bi2Se3 exhibits an extra hysteresis loop around zero field. The magnitude of the NPHE is found to scale inversely with carrier density. We speculate that the observed NPHE is related to the MPE-induced exchange gap opening and out-of-plane spin textures in the TI surface states, which may be used as an alternative transport signature of the MPE in MI/TI heterostructures.Item Second-harmonic signature of chiral spin structures in W/Pt/Co heterostructures with tunable magnetic anisotropy(Journal of Physics D: Applied Physics, 2023-03-28) Wang, Yang; Chan, Ying-Ting; Wang, Xiao; Wang, Tao; Cheng, Xuemei M.; Wu, Weida; Xiao, John Q.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 Néel-type domain walls, efficiently driven by nevertheless small SOTs in this double heavy metal heterostructure with canceling spin Hall angles.Item Spectroscopic aspects of magneto-transport responses in topological and magnetic heterostructures(University of Delaware, 2022) Wang, YangIn recent years, charge-spin interconversion phenomena have been intensively explored in the field of spin-orbitronics. The most essential goal is to generate spin currents through spin-orbit coupling (SOC) induced effects, e.g., spin Hall effect (SHE) in heavy metals, and utilize these spin currents to control the magnetization of an adjacent magnetic material. However, spin-charge interconversion in inversion symmetry broken systems with large SOC has far more fundamental aspects. ☐ In this thesis, we utilized magneto-transport measurements to investigate these phenomena in topological insulator (TI)/ferromagnet (FM) or transition metal (TM) heterostructures and heavy metal (HM)/FM multilayers, in both linear and nonlinear transport regimes. In TI heterostructures, we find under electrostatic perturbations imposed by deposition of nonmagnetic TMs, the quantum well states formed on the surface of TIs develop substantial Rashba spin-splitting, which is detected as a bilinear magnetoresistance. Under magnetic perturbations, the nonlinear planar Hall effect (NPHE) in the topological surface states is greatly enhanced, possibly reflecting the modified surface band structure due to time-reversal symmetry breaking. In a double HM/FM heterostructure where the magnetic anisotropy can be robustly tuned, we observed second-harmonic Hall voltage responses corresponding to domain wall structures with fixed chirality, stabilized by interfacial Dzyaloshinskii–Moriya interaction. And lastly, in the linear transport regime, we utilized inverse-SHE-induced anomalous Hall effect in Pt to probe the exchange bias on the surface of a doped magnetic insulator Tm3Fe5O12. ☐ The purpose of this series of studies is to first investigate the intricate mechanisms of nonreciprocal transport responses in noncentrosymmetric systems, and second to reveal the potential of using these responses to infer the band structures in momentum space or spin textures in real space. This makes the magneto-transport measurements an “electrical spectroscopy” method to assist the search for novel material systems for potential electronic or spintronic applications.