Magnetic resonance and microwave resistance modulation in the van der Waals ferrimagnet <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi mathvariant="normal">Mn</mml:mi> <mml:mn>3</mml:mn> </mml:msub> <mml:msub>

Unconventional magnetoresistance is a fascinating quantum phenomenon that continues to draw significant interest in condensed-matter physics. ${\mathrm{Mn}}_{3}{\mathrm{Si}}_{2}{\mathrm{Te}}_{6}$ has emerged as such a novel magnetoresistance (MR) material, notable for its largest MR exceeding conventional colossal magnetoresistance materials and pronounced directional anisotropy. Despite extensive research, the mechanisms driving MR in ${\mathrm{Mn}}_{3}{\mathrm{Si}}_{2}{\mathrm{Te}}_{6}$ remain elusive [Ni et al. Phys. Rev. B 103, L161105 (2021); Ye et al. Phys. Rev. B 106, L180402 (2022); Zhang et al., Nature 611, 467 (2022); Gu et al., Nat. Comm. 15, 8104 (2024)]. In this work, we explore the magnetic resonance of ${\mathrm{Mn}}_{3}{\mathrm{Si}}_{2}{\mathrm{Te}}_{6}$ and observe a reduced $g$ factor for magnetic fields applied along the crystalline $c$ axis compared to the ab plane, indicating a substantial orbital magnetization contribution along the $c$ axis. Furthermore, we detect resistance modulation under resonance conditions, suggesting that MR in ${\mathrm{Mn}}_{3}{\mathrm{Si}}_{2}{\mathrm{Te}}_{6}$ is sensitive to the out-of-plane spin polarization. These findings shed new light on the role of orbital magnetic moment in ${\mathrm{Mn}}_{3}{\mathrm{Si}}_{2}{\mathrm{Te}}_{6}$, offering a deeper understanding of the interplay between spin, orbital, and lattice degrees of freedom of electrons.