We study the relaxation dynamics of the electron system in graphene flakes
under Landau quantization regime using a novel approach of time-resolved Raman
scattering. The non-resonant character of the experiment allows us to analyze
the field dependence of the relaxation rate. Our results clearly evidence sharp
increase in the relaxation rate upon the resonance between the energy of the
Landau transition and the G-band and shed new light on relaxation mechanism of
the Landau-quantized electrons in graphene beyond the previously studied Auger
scattering
