Ultrafast photoinduced ferromagnetism in the perovskite manganite Gd0.55 Sr0.45 Mn O3

We report the ultrafast switching of the magnetic state in the course of photoinduced phase transition from an insulator with short-range charge and orbital order (CO/OO) to a ferromagnetic metal in perovskite-type Gd0.55 Sr0.45 Mn O3. The femtosecond Kerr rotation and reflectivity measurements, which detect the spin and charge dynamics, respectively, have revealed that the metallic state is formed within the time resolution (∼200 fs); however, magnetization increases with the time constant of 0.5 ps. The relatively slow increase of the magnetization is attributable to the magnetic-field-induced alignment of ferromagnetic domains in the initially produced metallic state.