Ren, He2026-03-042026-03-042026-03-042026-02-11https://hdl.handle.net/10012/22962Magnetic random-access memory (MRAM) is a leading candidate for next-generation non-volatile memory due to its fast switching speed, high endurance, and compatibility with CMOS technology. Spin–orbit torque (SOT) provides an efficient and reliable purely electrical means for magnetization switching in MRAM devices; however, deterministic switching of perpendicular magnetic anisotropy (PMA) bits typically requires an external magnetic field, which complicates device integration. Achieving field-free SOT switching through materials and symmetry engineering is therefore a critical challenge for scalable spintronic memory and logic applications. Transition metal dichalcogenides (TMDs) are a versatile class of layered materials whose electronic and magnetic properties can be dramatically modified through intercalation. Among them, self-intercalated chromium tellurides Cr1+δTe2 have attracted increasing attention due to their intrinsic ferromagnetism, structural compatibility with telluride-based materials, and potential for spintronic applications. In parallel, topological insulators such as (Bi0.75Sb0.25)2Te3 host spin–momentum–locked surface states that enable highly efficient charge-to-spin conversion, providing a powerful platform for SOT-based devices. In this thesis, the epitaxial growth of both Cr3Te4 and (Bi0.75Sb0.25)2Te3 thin films is demonstrated. Their high crystalline quality is verified through detailed structural and electronic characterization, establishing a reliable materials platform for subsequent heterostructure fabrication and symmetry-engineered SOT studies. A pronounced Kondo-like resistivity upturn is observed in ultrathin (< 12 monolayers) Cr3Te4 films grown on sapphire substrates. Low-temperature transport measurements are well described by a Kondo model, while the effect is suppressed in thicker films. Scanning tunneling microscopy reveals defect-induced electronic states consistent with Kondo scattering, and cross-sectional transmission electron microscopy shows that structural defects are concentrated at the film–substrate interface, providing localized magnetic disorder responsible for the observed behavior. The self-intercalation induced flatbands further enhance the electron-spin correlations. Moreover, the presence of Kondo scattering enhances current-induced spin accumulation, which is beneficial for SOT efficiency. Finally, deterministic, field-free switching of perpendicular magnetization using SOT is demonstrated in Cr3Te4/(Bi0.75Sb0.25)2Te3 heterostructures. While the topological insulator surface states enable efficient charge-to-spin conversion, deterministic out-of-plane switching requires additional in-plane symmetry breaking. The ordered 2×1 self-intercalation structure of Cr3Te4 introduces the necessary symmetry reduction, resulting in a unidirectional mirror symmetry m (Cs) at the interface. This enables robust field-free switching of a high-coercivity (∼ 1.3 T) perpendicular ferromagnet. Wafer-scale growth produces three equivalent 2 × 1 domains, giving rise to a characteristic three-fold angular dependence in the SOT response. Together, these results establish a novel and practical route to engineering topological insulator heterostructures as a multifunctional platform for studying correlated electron phenomena and engineering efficient, field-free spintronic devices.enspin-orbit torquespintronic devicesmagnetoresistive random access memorytopological insulatortransition metal dichalcogenideDoctoral Thesis