Photoinduced resistivity change in layered manganite La2−2xCa1+2xMn2O7 (x=0.3)

Photoinduced effect on the resistivity in layered perovskite manganite La2−2xCa1+2xMn2O7 (x=0.3) has been studied by using a He–Ne laser (632.8 nm) in the temperature range from 20 to 300 K and an applied magnetic field of 5000 G. In both cases of zero magnetic field and applied magnetic field, the resistivity peaks of the sample shift to lower temperatures slightly under the irradiation of the laser. The photoinduced resistivity is negative and positive for the paramagnetic semiconductive regime and the ferromagnetic metal regime, respectively. The variation of the resistivity and magnetoresistance induced by laser irradiation is explained in terms of the effect of the low-dimensional composite polarons.