Critical behavior of a photo-disordered spin system in epitaxial CrO2 films

We have investigated dynamical properties of the spin system in a ferromagnetic CrO2 thin film by means of a nanosecond pump–probe method. The absorption spectrum consists of both temperature-dependent and -independent components, which indicates a characteristic electronic structure with localized and itinerant spins in a double-exchange system. With strong pulse excitations we have observed absorption changes reflecting photo-induced spin disorder in the ferromagnetic phase. The temperature variation of the relaxation time near the Curie temperature shows a critical slowing down of the relaxation time near the phase transition. The critical exponent obtained is 0.18±0.01.