Electrical transport properties in La_0.7Ca_0.3-xSr_xMnO₃ thin films

The influence of the chemical composition on the structure, magnetic and electrical transport properties of La_0.7Ca_0.3-xSr_xMnO₃ (LCSMO, x≤0.05) thin films was systematically studied. LCSMO thin films were prepared by Sol-Gel method. XRD results show that all the films have typical perovskite structure. With increase of Sr doping concentration, both Curie temperature T_C and metal-insulator transition temperature T_MI of LCSMO thin films increase monotonously. When Sr doping concentration x≤0.05, with increase of temperature, absolute value of MR decreases first, then increases to a maximum value around T_MI, and finally decreases, which indicates that the disorder coming from phase separation around T_MI contributes greatly to MR. The field dependence of MR values at certain temperature can be classified into two kinds. When the temperature is much lower than T_MI, dual gradient of MR with the magnetic field is shown. The tunneling effect on the grain boundaries plays a dominant part in the low magnetic field, and this effect is particularly sensitive to the magnetic field; the suppression of spin fluctuations by magnetic field is the main reason in the high magnetic field range. When the temperature is higher than T_MI, MR of LCSMO thin films changes almost linearly with the magnetic field which is mainly due to suppression of spin fluctuations by magnetic field.