Ultrafast spin dynamics in ferrimagnets underpin high-speed spintronic devices that combine rapid magnetic dynamics with finite magnetization for electrical detection. Here we investigate the ultrafast magnetization and lattice dynamics in ferrimagnetic antiperovskite ${\mathrm{Mn}}_4\mathrm{N}$ epitaxial thin films on ${\mathrm{SrTiO}}_3$ using time-resolved magneto-optical Kerr spectroscopy. Structural characterization reveals a tetragonal distortion induced by epitaxial tensile strain, which stabilizes strong perpendicular magnetic anisotropy. Following femtosecond optical excitation, the magnetization exhibits an ultrafast demagnetization with a characteristic time of $\sim 190\mathrm{fs}$, followed by two recovery components with different timescales, which suggest temporally distinct responses of the inequivalent Mn sublattices. Field-independent demagnetization dynamics indicate that the process is governed primarily by intrinsic electronic scattering rather than external magnetic perturbations. We further demonstrate gigahertz spin precession frequencies and remarkably low Gilbert damping ($\sim 0.02$). In addition, coherent acoustic phonon modes in the tens-to-hundreds of GHz range are detected, revealing temperature-dependent lattice softening. These results provide insight into the coupled spin-lattice dynamics of rare-earth-free ferrimagnetic nitrides and highlight ${\mathrm{Mn}}_4\mathrm{N}$ as a promising platform for ultrafast spintronic applications.

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• Spintronics
• Ultrafast magnetization dynamics
• Ferrimagnets
• Magnetic thin films
• Nitrides
• Magneto-optical Kerr effect
• Molecular beam epitaxy