  A coherent THz optical lattice mode is triggered by femtosecond laser pulses
in the antiferromagnetic van der Waals semiconductor FePS$_3$. The 380 nm thick
exfoliated flake was placed on a substrate and laser-driven lattice and spin
dynamics were investigated as a function of the excitation photon energy and
sample temperature. The pump-probe spectroscopic measurements reveal that the
photo-induced phonon is generated by a displacive mechanism. The amplitude of
the phononic signal decreases as the sample is heated up to the N\'eel
temperature and vanishes as the phase transition to the paramagnetic phase
occurs. This evidence confirms that the excited lattice mode is intimately
connected to the long-range magnetic order. Therefore our work discloses a
pathway towards a femtosecond coherent manipulation of the magneto-crystalline
anisotropy in a van der Waals antiferromagnet. In fact, it is reported that by
applying a magnetic field the induced phonon mode hybridizes via the
Kittel-mechanism with zone-centre magnons.
