Photoinduced Spin Fluctuation in a Ferromagnetic Manganite Film

The transmission and resistance in a La0.6Sr0.4MnO3 film (Tc similar to 325 K) have been investigated under photo-irradiation at various temperatures by means of time-resolved pump-probe method. Below Tc, we have observed a negative transient transmission change Delta T/T at 2.54 eV as well as a positive resistance change Delta R/R under photo-irradiation at excited energy E-exc = 3.20 eV. With increasing the temperature to Tc, the Delta T/T shows a significantly reduction. We have further found that the photoinduced Delta R/R is suppressed with increase of the applied dc current I at 295 K. We have ascribed the photoinduced Delta T/T and Delta R/R of the La0.6Sr0.4MnO3 film to the spin fluctuation in the ferromagnetic phase.