Ultrafast spin dynamics and critical behavior in half-metallic ferromagnet: Sr2FeMoO6

Ultrafast spin dynamics in ferromagnetic half-metallic compound Sr2FeMoO6 i s investigated by pump-probe measurements of the magneto-optical Kerr effec t. The half-metallic nature of this material gives rise to anomalous therma l insulation between spins and electrons and allows us to pursue the spin d ynamics from a few to several hundred picoseconds after the optical excitat ion. The optically detected magnetization dynamics clearly shows the crosso ver from microscopic photoinduced demagnetization to macroscopic critical b ehavior with universal power law divergence of relaxation time for a wide d ynamical critical region.