We have demonstrated the ultrafast switching of the magnetic state from a spin glass insulator with short range charge and orbital order (CO/OO) to a ferromagnetic metal in the course of photoinduced phase transition utilizing the strong phase competition in perovskite-type Gd0.55Sr0.45MnO3. The femtosecond Kerr rotation and reflectivity measurements, which detect the spin and charge dynamics, respectively, have revealed that the metallic state is formed just after the photoirradiation, however, magnetization increases with the time constant of 0.5 ps. The delayed increase of the magnetization is attributable to the magnetic-field-induced alignment of ferromagnetic domains in the initially produced metallic state.
