Mechanism of Anomalous Anisotropic Colossal Magnetoresistance in Quasi-2D Mn₃Si₂Te₆ Bulk Single Crystal

Mn₃Si₂Te₆, quasi-2D ferrimagnetic semiconductor, exhibits anomalous saturated colossal magnetoresistance (CMR) only when a magnetic field is applied along its magnetic hard magnetization axis, suggesting unconventional underlying physics and promising potential for spintronic applications. However, the intrinsic mechanism behind this anomalous anisotropic CMR remain unresolved. In this work, the temperature and angular dependencies of magnetoresistance (MR) in high-quality Mn₃Si₂Te₆ single crystals are systematically investigated. The MR measured within the easy ab-plane shows no saturation, whereas a large negative saturation MR of ≈ -100% is observed along the hard magnetization c-axis below the Curie temperature. To explain this behavior, a novel model is proposed in which in-plane magnetic fields induce quasi-2D magnetotransport, while out-of-plane fields promote a transition to 3D transport. Notably, when the c-axis field exceeds the demagnetizing field, the alignment between spin-polarized carriers and magnetic moments significantly suppresses scattering. The results challenge the applicability of the chiral orbital currents (COC) model in Mn₃Si₂Te₆ single crystals and establish a new framework for controlling the CMR effect in layered magnets, offering a pathway toward future spintronic technologies.