Tunable magnetic and magnetotransport properties in locally epitaxial La_0.67Sr_0.33MnO₃ thin films on polycrystalline SrTiO₃, by control of grain size

Abstract

La0.67Sr0.33MnO3 (LSMO) thin films have been grown by pulsed laser deposition on SrTiO3 using combinatorial substrate epitaxy (CSE) approach, i.e. polycrystalline substrates with micrometer-size grains. The crystallographic domains size of those polycrystalline substrates can be controlled between 2 to 45 µm depending on the annealing temperature during synthesis. Each grain of the substrate acts as a single crystalline growth template promoting local epitaxy with a reproduction of the substrate grain structure in the thin film. Therefore, a fine-tuning of the substrate grain metrics and high crystalline quality of locally epitaxial LSMO film, allows to combine the advantages of polycrystalline, i.e. the presence of low field magnetoresistance (LFMR) and the possibility to use very thin films, with a pronounced magnetic shape anisotropy. For this, the magnetic and transport properties of the films are showing a strong influence with varying grain metrics of the substrate. High Curie temperatures, important values of the LFMR and anisotropy for optimized substrate grain metrics with the relative orientation of the magnetic field to the film plane underline the high quality of the films and the advantage of the CSE approach. The obtained LSMO thin films may have an interest for high-resolution low field magnetic sensors application.

Modeling of SrTiO3 polycrystalline substrate grain growth for tuning thin film functional properties

“…The grain metric is important for the introduction of grain boundaries and the tunability of the thin films functional properties. For example, those grain boundaries can bring extrinsic properties to the thin films such as in LSMO, which are not present for single crystal films (see figure 7) [10]. As we can see, at low temperature, single crystal films present a very small MR, whereas, the polycrystalline substrates induce new effect on the LSMO films with low field Magnetoresistance (LFMR), and an important MR. More importantly, those effects can be tuned by their density in the films as seen on figure 7, where this MR tends to increase with the decrease of the grain size and therefore the importance of the grain metric control of the polycrystalline substrates.…”

“…All STO ceramics were synthetized starting from the two precursors TiO2 and SrCO3 [10]. These precursors were calcined for 12 hours at 1200 °C.…”

“…More recently, another degree of freedom of those substrates was explored with the control of the grain metrics as it can be used as a new tuning factor for functional properties. This is particularly true for thermoelectric properties in SrRuO3 thin films, where the long-range translational symmetry breaking modifies the properties compared to single-crystal films [9], or for magneto-resistive properties in La0.7Sr0.3MnO3 thin films with different domain grain sizes from 2 m to 45 m [10].…”