Ultrafast demagnetization for Ni₈₀Fe₂₀ and half-metallic Co₂MnSi Heusler alloy films

We investigated ultrafast demagnetization for NM/Ni₈₀Fe ₂₀ (Py)/NM (NM=Ta,Pt) and epitaxial half-metallic Co₂MnSi (CMS) films using an all-optical pump-probe technique to clarify the correlation between demagnetization time τ_M and magnetic damping constant α or spin polarization. The signal from the all-optical time-resolved magneto-optical Kerr effect exhibited rapid decrease in the sub-ps time regime and damped oscillations for these films. Values of τ_M and α were evaluated using the three- temperature model and the Landau-Lifshitz- Gilbert equation. The α values for the NM/Py/NM films depended on both the Py thickness and NM materials while τ_M was almost constant. The τ_M values for the epitaxial CMS films were almost independent of L2₁-ordering and a little shorter than those for NM/Py/NM films.