Photoinduced magnetization following a stretched exponential growth with time is observed in ${\mathrm{La}}_{0.9}{\mathrm{Ca}}_{0.1}{\mathrm{MnO}}_3$ films exposed to near infrared light in magnetic fields of $\mathit{B}⩾0.1\mathrm{mT}$. The magnetic irreversibility observed below 56 K between zero-field-cooled and field-cooled films is strongly influenced by illumination, giving space to a persistent magnetic state with increased ferromagnetic interactions, modified magnetic anisotropy and decrease of the blocking temperature to 5 K. When the illumination and the magnetic field are removed the magnetization of the films decays very slowly after a short period of fast relaxation but recovers the original level when the field is applied again. Such behavior obeys predictions for domain pinning in narrow-wall random-field Ising systems. The results suggest trapping of photogenerated electrons by magnetic disorder while the holes contribute to growth of ferromagnetism in the films.

• Received 27 January 2005

DOI:https://doi.org/10.1103/PhysRevB.71.132404