Investigation of Magnetoresistance and Spin-Orbit Torques in Bi2Se3/Permalloy Heterostructures at Room Temperature

Topological insulator (TI)/ferromagnet (FM) heterostructures provide an exceptionally promising platform for next-generation, energy-efficient spintronic memory and logic architectures due to their strong spin-orbit coupling and spin-momentum locked surface states. In this study, we systematically investigate the magnetoresistance and spin-orbit torque (SOT) generation in Bi₂Se₃/Permalloy (Py; Ni₈₀Fe₂₀) bilayers at room temperature (300 K). High-quality Bi₂Se₃ thin films (8–20 nm) were grown on Al₂O₃ (0001) substrates via molecular beam epitaxy, capped in situ with Py (5 nm) and an Al₂O₃ protective layer. Angle-dependent magnetoresistance and spin-torque ferromagnetic resonance (ST-FMR) measurements reveal pronounced spin Hall magnetoresistance (SMR) and highly efficient spin-charge interconversion. Second-harmonic Hall voltage analyses resolve both damping-like and field-like effective fields, yielding an effective damping-like spin Hall torque efficiency (\theta_{DL}) of approximately 0.52 ± 0.04 at room temperature, notably surpassing conventional 5d heavy metals such as Pt and Ta. Interfacial Gilbert damping enhancement demonstrates substantial interfacial spin transparency (T_{int} ≈ 0.48). Our findings demonstrate that despite thermally activated bulk conduction in Bi₂Se₃ at ambient conditions, robust topological surface states and interfacial Rashba-Edelstein effects govern charge-to-spin conversion, validating Bi₂Se₃/Py heterostructures as viable candidates for room-temperature, low-power SOT-MRAM technologies.