Wavelength scaling of ultrafast demagnetization in Co/Pt multilayers

Ultrafast demagnetization, a phenomenon of utmost interest in the context of optical control of magnetically recorded data, has been extensively studied in a variety of different materials. However, only a limited number of studies have investigated the impact of the pump laser wavelength on the process, and only within a narrow spectral range. Performing resonant scattering experiment at the cobalt M-2,M-3 edges, using extreme ultraviolet radiation photons from a high harmonic source, we studied the ultrafast demagnetization dynamics of Co/Pt multilayers by tuning the pump wavelength to 0.4, 0.8, and 1.8 mu m. We show that the degree of demagnetization at short time scale (100s of fs) is stronger at longer wavelengths. This is explained by the wavelength dependence of both the laser induced heating of the electrons (T-e proportional to lambda(2)) and the spatial distribution of the electromagnetic energy deposited into the multilayer sample.