Ultrafast Demagnetization for Ni80Fe20 and Half-metallic Co2MnSi Heusler Alloy Films

We investigated ultrafast demagnetization for NM/Ni80Fe20 (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 tau(M) and magnetic damping constant alpha 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 tau(M) and alpha were evaluated using the three-temperature model and the Landau-Lifshitz-Gilbert equation. The alpha values for the NM/Py/NM films depended on both the Py thickness and NM materials while tau M was almost constant. The tau(M) values for the epitaxial CMS films were almost independent of L2(1)-ordering and a little shorter than those for NM/Py/NM films.