Unravelling the effect of SrTiO₃antiferrodistortive phase transition on the magnetic properties of La_0.7Sr_0.3MnO₃thin films

Abstract

Epitaxial La0.7Sr0.3MnO3 (LSMO) thin films, with different thickness ranging from 20 nm up to 330 nm, were deposited on (100)-oriented strontium titanate (STO) substrates by pulsed laser deposition, and their structure and morphology characterized at room temperature. Magnetic and electric transport properties of the asprocessed thin films reveal an abnormal behavior in the temperature dependent magnetization M(T) below the antiferrodistortive STO phase transition (TSTO) and also an anomaly in the magnetoresistance and electrical resistivity close to the same temperature. Up to 100 nm LSMO thin films, an in-excess magnetization and pronounced changes in the coercivity are evidenced, achieved through the interface-mediated magnetoelastic coupling with antiferrodistortive domain wall movement occurring below TSTO. Contrarily, for thicker LSMO thin films, above 100 nm, an in-defect magnetization is observed. This reversed behavior can be understood within the emergence in the upper layer of the film, observed by high resolution transmission electron microscopy, of a branched structure needed to relax elastic energy stored in the film which leads to randomly oriented magnetic domain reconstructions. For enough high-applied magnetic fields, as thermodynamic equilibrium is reached, a fully suppression of the anomalous magnetization occurs, wherein the temperature dependence of the magnetization starts to follow the expected Brillouin behavior.

Ordered La0.7Sr0.3MnO3nanohole arrays fabricated on a nanoporous alumina template by pulsed laser ablation

“…Such magnetic phase separation reduces T C when compared to the continuous LSMO/MgO thin films. This reduction in T C is also much lower compared to other LSMO continuous thin films reported with different substrates [21,24,26]. Such reduction in the T C value can also be explained by the voids which create a magnetic pinning effect and thereby reduce the domain size as reported earlier [5,9,29].…”

“…That magnetic pinning effect obtained by nanoholes not only decreases the T C but also enhances the H C values as shown in figure 5(b). Compared with the continuous thin films deposited on MgO and with other different substrates, the H C values are significantly higher for nanohole arrays [21,24].…”

“…To better clean the substrates, they were kept at 700 C for 30 min before deposition, for degasification. These preparation conditions allow the preparation of dense, homogeneous LSMO thin films, with low droplet density in a controlled way [21,22]. To prevent under-oxidation of the films after deposition they were cooled down to room temperature, at a rate of 7 C min −1 , under an atmospheric oxygen pressure.…”

Impact of growth kinetics on the interface morphology and magnetization in La1/3Sr2/3FeO3/La2/3Sr1/3MnO3 heterostructures

“…Figures 8(c) and (d) show the magnetization depth profile in µ B /Mn atom also obtained from the simulations. Temperatures greater than 100 K were chosen to avoid an additional strain effect due to the antiferrodistortive phase transition in STO which adversely influences the magnetization in LSMO [42]. In order to study the coupling effect between the electronic states within the LSFO layer and the magnetization of the LSMO layer the measurements are done at temperatures above (250 K), near (200 K) and below (110 K and 150 K) the Verwey transition of LSFO.…”