Abnormal Hot Carrier Decay via Spin-Phonon Coupling in Intercalated van der Waals Ferromagnetic Fe_1/3TaS₂

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 ΔR(t)/R₀ time series in ferromagnet Fe_1/3TaS₂, which is a result of the lattice of TaS₂ vdW layer transfering its energy to spin via spin-phonon coupling. The Fe ions inserted between TaS₂ vdW layers with very weak bonding with TaS₂ 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 Fe_1/3TaS₂.