In the ferrimagnetic semiconductor ${\mathrm{Mn}}_3{\mathrm{Si}}_2{\mathrm{Te}}_6$, a colossal magnetoresistance (CMR) is observed only when a magnetic field is applied along the magnetic hard axis ($\mathbf{H}\parallel c$). This phenomenon suggests an unconventional CMR mechanism potentially driven by the interplay between magnetism, topological band structure, and/or chiral orbital currents (COC). By comparing electrical resistance measurements using continuous direct currents and pulse currents, we found that the current-induced insulator-metal transition, supporting the COC-driven CMR mechanism, is likely a consequence of Joule heating effects. First-principles calculations reveal a pronounced band-gap reduction upon tilting the magnetic moments toward the $c$ axis, accompanied by increased carrier concentration and Fermi velocity. Combining spin-orientation-dependent electronic structure with Boltzmann transport theory, the calculated electrical resistance closely reproduces the CMR observed experimentally. These findings suggest that the CMR in ${\mathrm{Mn}}_3{\mathrm{Si}}_2{\mathrm{Te}}_6$ stems primarily from band-gap reduction induced by partial polarization of magnetic moments along the magnetic hard axis.

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• Electrical properties
• Magnetism
• Magnetotransport
• Phase transitions
• Topological materials