Direct observation of percolation in a manganite thin film

Upon cooling, the isolated ferromagnetic domains in thin films of La0.33Pr0.34Ca0.33MnO3 start to grow and merge at the metal-insulator transition temperature T-P1, leading to a steep drop in resistivity, and continue to grow far below T-P1. In contrast, upon warming, the ferromagnetic domain size remains unchanged until near the transition temperature. The jump in the resistivity results from the decrease in the average magnetization. The ferromagnetic domains almost disappear at a temperature T-P2 higher than T-P1, showing a local magnetic hysteresis in agreement with the resistivity hysteresis. Even well above T-P2, some ferromagnetic domains with higher transition temperatures are observed, indicating magnetic inhomogeneity. These results may shed more light on the origin of the magnetoresistance in these materials.