Photoinduced formation of ferromagnetic clusters in La 0.9 Ca 0.1 MnO 3 thin films

Microwave losses due to conductivity and magnetic permeability are investigated in La0 9Ca0 jMn0 3 films illuminated with photons in the energy range o f E = 0 .5-2 eV. Growth of photoinduced ferromagnetic hysteresis is observed when the magnetic field is swept between —15 and 15 mT at temperatures below 60 K. The time required for saturation of the opening of the hysteresis loop depends on the photon energy having the minimum of =40 s at the illumination intensity 7 = 3.5X10 photons/cnrs. Both photoinduced magnetization and the increase of microwave photoconductivity can be well explained with a model assuming that small ferromagnetic regions exist within an insulating ferromagnetic phase of the sample and that these regions are expanded by optically induced charge transfer between Jahn-Teller split e states of neighboring Mn + ions.