Spectroscopic aspects of magneto-transport responses in topological and magnetic heterostructures
Date
2022
Authors
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Publisher
University of Delaware
Abstract
In 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.
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Keywords
Band structure, Magneto-transport measurements, Spin texture, Spin-orbit coupling, Topological, Electrical spectroscopy