Time resolved ultrafast demagnetization of Co2MnSi observed by X-ray magnetic circular dichroism and an ultrafast streak camera

The demagnetization dynamics of the Heusler alloy Co2MnSi and a ferromagnetic metal Ni was studied using picosecond time-resolved X-ray Magnetic Circular Dichroism. Femtosecond (fs) laser pulses were used to generate a magnetic phase transition in the samples and their demagnetization time constants compared in order to investigate the effect of electronic density of states (DOS) on the demagnetization mechanisms. In contrast to the sub-picosecond demagnetization of the metal ferromagnet Ni, a substantially slower demagnetization time constant of 3.5+/-0.5 ps was measured for the Heusler alloy, implying that the half metallic character of Co2MnSi inhibits spin-flip scattering of hot electrons. As a result, a bottleneck must be created and a new demagnetization process used in the transfer of angular momentum between the spin system and the lattice.