Role of epitaxy and polycrystallinity in the magnetoresistance and magnetization of La0.8Sr0.2MnO3 thin films

Abstract

La_0.8Sr_0.2MnO₃ thin films were simultaneously deposited by pulsed laser ablation on silicon (Si) and LaAlO₃ (LAO) substrates. Films on Si were polycrystalline while those on LAO were (100) epitaxial with an in‐plane correlation length of ≊10 nm. The magnetization and magnetoresistance behavior of these two films were significantly different. Both films exhibit antiferromagnetic–ferromagnetic transitions—at different temperatures [180 K (LAO); 230 K (Si)]—and their magnetic moments at 10 K were significantly different (Si—0.0035 emu; LAO—0.0022 emu). However, both films showed significant high field slope in magnetization at 10 K. Significant fractions of both films remain antiferromagnetic at low temperatures and hence net susceptibilities, dependent on the direction of the applied magnetic field, are different for the epitaxial (LAO) and randomly oriented polycrystalline (Si) films. The magnetoresistance peak, corresponding to the semiconductor–metal transition is observed at 170 and 130 K for the epitaxial (LAO) and polycrystalline (Si) films, respectively. Moreover, their resistance values are two orders of magnitude different (Si—MO/hms; LAO—KOhms). These properties can be interpreted in terms of the major role of grain boundaries in determining the scattering as well as possible differences in O₂ stoichiometry.