Abnormal Hot Carrier Decay via Spin-Phonon Coupling in Intercalated van der Waals Ferromagnetic FeTaS.

Spin-phonon coupling is a fundamental interaction in ferromagnets/antiferromagnets and plays a key role in hot carrier decay. Normally, spin transfers its excess energy to a lattice via spin-phonon coupling in hot carrier decay in ferromagnets/antiferromagnets. However, the reverse energy transfer process (i.e., from lattice to spin) is feasible in principle but rarely reported. Here, we observe an abnormal hot carrier decay with a slow fall (80 ps) in Δ()/ time series in ferromagnet FeTaS, which is a result of the lattice of TaS vdW layer transfering its energy to spin via spin-phonon coupling. The Fe ions inserted between TaS vdW layers with very weak bonding with TaS vdW layer, are the origin of the ferromagnetism and give rise to its weak electron-spin and spin-phonon couplings which in turn lead to the observed abnormal hot carrier decay in the ferromagnetic phase FeTaS.