Interplay of spin polarization, Gilbert damping and ultrafast demagnetization in Heusler compounds Since the discovery of all-optical control of STRUCTURE AND ELECTRONIC PROPERTIES the magnetization in magnetic layers using The thin films’ structure was carefully analyzed using electron and laser pulses, many efforts have been made X-ray diffraction together with transmission electron microscopy to understand the underlying ultrafast at the Institut Jean Lamour. Although a B2-type chemical disorder (Mn/Si/Al mixture) is obtained when substituting Si by dynamics responsible for the transfer and Al [3], the high crystalline quality and the Heusler structure are dissipation of spin angular momentum. Here, preserved for the entire substitution range x, as shown in figure tailored CoMnAlSi epitaxial Heusler 1-a. This series of compounds was elaborated at the Cassiopée 2 x 1-x beamline MBE chamber, where the spin polarization P of the films are used to adjust the degree of spin electronic states near E was measured using in-situ spin-F polarization at the Fermi energy P and resolved photoemission spectroscopy. Figure 1-b shows that Gilbert damping α, and to study the impact controlling the amount of Al substitution in these compounds allows a tuning of the spin polarization from a half-metal magnetic of these two parameters on the ultrafast behavior with P = 100% (spin gap) to a standard magnetic demagnetization time τ . The latter is material with P = 60 %. Moreover, broadband ferromagnetic M resonance measurements shown in figure 1-b demonstrates shown to be inversely proportional to 1-P and that the Gilbert damping parameter of these alloys is among consequently to α, suggesting a similarity the lowest reported for conductive layers [3], and that it is in the spin momentum dissipation processes inversely proportional to the measured spin polarization. The involved in these two effects that live on high versatility of this class of compounds make them excellent candidates to evaluate the impact of the electronic structure different timescales. on the ultrafast magnetization dynamics. Manipulation of the magnetization on the femtosecond timescaleFIGURE 1 has become an outstanding challenge since the demonstration of sub-picosecond magnetization quenching [1] and magnetization reversal [2]. Despite the theoretical and experimental work that has been reported up to now, the relationship between the spin polarization of electronic states at the Fermi energy (E) orF the magnetic damping and ultrafast demagnetization excited by femtosecond laser pulses remains unclear. In the present work, we used CoMnAlSi2 1-xquaternary Heusler compounds grown by Molecular Beam Epitaxy (MBE) as a playground tox test this dependency and get further insights into the relaxation processes involved in this new light-matter interaction. 20