Interface-Engineered Weak Fermi-Level Pinning and Spin-Dependent Schottky Barriers in M/LaBr2 (M = Ag, Co, Cu, Ni) Heterojunctions for Multifunctional Spintronics

Metal-induced gap states (MIGS) and Fermi-level pinning (FLP) are major obstacles to achieving optimal spin injection efficiency at metal/magnetic semiconductor interfaces. This study demonstrates that integrating the transition metals (Ag, Co, Cu, and Ni) via van der Waals interactions with the two-dimensional bipolar magnetic semiconductor monolayer LaBr2 effectively suppresses these detrimental interfacial effects. The weak interlayer orbital hybridization drastically restrains MIGS generation and yields nearly ideal FLP with a pinning factor S ≈ 0.99, approaching the ideal Schottky–Mott limit. This high-quality interface preserves the intrinsic spin-split band structure of LaBr2, facilitating strongly spin-dependent Schottky barriers. Particularly, the Ni/LaBr2 junction exhibits a near-Ohmic contact for spin-up holes (0.03 eV barrier) and a Schottky barrier for spin-down electrons (0.21 eV barrier), enabling near-unity spin-filtering efficiency. Leveraging this asymmetry, we design a dual-gate Ni/LaBr2 field-effect transistor that generates 100% spin-polarized currents under uniform gate biases and switches to a high-resistance state under opposing biases, achieving on/off ratios up to 105 at a low bias of 0.08 V. This device successfully integrates spin-filtering and spin-valve functionalities within a single architecture. Although the intrinsic Curie temperature (≈280 K) necessitates post-synthetic enhancement for room-temperature operation, this study establishes an interfacial design paradigm and material platform for developing low-power, integrated multifunctional spintronic devices.