Substrate-Dependent Microstructure and Magnetoresistance of La–Sr–Mn–O Thin Films Grown by RF Sputtering

The relationship between the microstructure and the magnetoresistive properties of La–Sr–Mn–O thin films was investigated. La0.76Sr0.24Mn0.98O3-δ films were deposited onto (100) SrTiO3, (100) LaAlO3, (110) sapphire and polycrystalline YSZ substrates by rf sputtering. The films grew epitaxilly on SrTiO3 and LaAlO3 substrates with a large number of defects, whereas in-plane-oriented and nonoriented polycrystalline films with 20–60 nm grains grew on the sapphire and polycrystalline YSZ substrates, respectively. The magnetoresistance ratio (H=0.8 T) of the epitaxial films has a peak at a temperature slightly below the maximum resistance temperature. The resistivity of the epitaxial films was ten times less than that of the polycrystalline films. The polycrystalline films exhibited substantial magnetoresistance ratios over a wide temperature range. The existence of grain boundaries and the preferential in-plane grain orientation were found to be correlated to the resistivity, temperature dependence and low magnetic field sensitivity of magnetoresistance.