Fan, Yihong2024-02-092024-02-092023https://hdl.handle.net/11299/260629University of Minnesota Ph.D. dissertation.--- 2023. Major: Electrical Engineering. Advisor: Jian-Ping Wang. 1 computer file (PDF); xii, 141 pages.Spin-orbit torque (SOT) materials and devices have become one of the most promising candidates for future memory and computing systems due to their high endurance, high speed, high storage density, and low energy consumption. However, using the three-terminal magnetic tunnel junction structure for read out has become one of bottlenecks for the application of any SOT devices. Two-terminal SOT unit with the same read and write lines needs to be developed. The unidirectional spin Hall magnetoresistance (USMR) is a prospective candidate to read the magnetization with a two-terminal configuration.Unidirectional magnetoresistive behaviors, including USMR, unidirectional magnetoresistance (UMR), and bilinear magnetoelectric resistance (BMER), have drawn attention not only due to their potential application but also for their fascinating physics. Observed in a variety of materials, unidirectional magnetoresistive behaviors can originate from different contributions including electron accumulation, magnons, spin momentum locking, and spin-orbit torque. This dissertation studied the unidirectional magnetoresistive behaviors, including USMR, UMR, and BMER, from several aspects: physics, materials, characterization, and applications. A universal DC characterization method is developed for the field-dependent measurement of unidirectional magnetoresistive behaviors in different materials, which provides a standard way to study different contributions in unidirectional magnetoresistive behaviors. The material selection for USMR, UMR and BMER has been largely broadened through this research. USMR is first observed in amorphous PtSnx, which reaches a value of 0.7×10-11 per current density (A/cm2). UMR is first observed in antiferromagnetic Fe2O3, which may be attributed to an interplay of enhanced Rashba effect by spin canting and the contributions of magnons. Moreover, BMER is observed in a single layer topological semimetal Pt3Sn for the first time and is found to be enhanced by ~2 times with an adjacent ferromagnetic layer. This finding provides a new approach to manipulating BMER value through opening the band gap of the topological states. This dissertation clarifies the measurement of unidirectional magnetoresistive behaviors and explores USMR, UMR, and BMER in multiple novel SOT material systems, which may shed light on how to further increase USMR and/or UMR value for practical applications.enThesis or Dissertation