Single-axis control of manganite films by helium doping via He-co-sputtering

We have studied the effect of the out-of-plane lattice on tensile strained (001) La0.7Ca0.3MnO3 thin films. The films were deposited on SrTiO3 substrates through magnetron sputtering technique under different Ar/O2/He gas flow ratios, varying the out-of-plane lattice from 3.823 Å to 3.845Å, which corresponds to an increase in the metal-insulator transition temperature. These changes are reversible after high-temperature anneal due to a massive helium release from the films occurring at temperatures around 540°C. The dependence of the transition temperature on lattice distortion is in good agreement with the prediction proposed by Millis et al. [J. Appl. Phys. 83, 1588 (1998)]. Considering the Jahn-Teller distortion enhanced by the in-plane biaxial strain in the films, we attribute the elevated transition temperature to the distortion relaxation due to He doping in the tensile strained films. The effective He doping by magnetron sputtering technique provides a simple strategy for manipulating functionality of oxide films.