Crystallinity, surface morphology, and magnetic properties of La0.7Sr0.3MnO3 thin films: An approach based on the laser ablation plume range models

Abstract

We report on a systematic investigation of the influence of pulsed laser deposition (PLD) parameters upon the microstructure, surface morphology, and magnetic properties of La0.7Sr0.3MnO3 (LSMO) thin films grown on (100) SrTiO3 substrates. The optimization of the physical properties requires a careful exploration of the main parameters such as the oxygen pressure P and the target-to-substrate distance D. We show that there is a strong correlation between both these parameters and an optimal distance (D=L0), which can be calculated from a PD3 scaling law (in accordance with a shock wave model). This particular value L0 corresponds to the distance for which all species are thermalized in the plume. In the D–P diagram, L0 defines two distinct regions for the morphology and the microstructure: (i) when D<L0, the films exhibit a dense, smooth (Rrms∼0.1 nm) and large grain (Φ>1 μm) morphology. These films are perfectly epitaxial on the substrate, single-phase and not relaxed. (ii) When D≫L0, the films are columnar with a high peak-to-peak roughness (Rp-v>10 nm). While a good surface morphology and an good internal microstructure are obtained in the low P and D part of the diagram, on the opposite, the best magnetic and electrical properties are observed in films deposited in a sharp transition window between these two regions.