Abstract
A previously unreported tetragonal phase has been discovered in a epitaxially strained GdMnO3 thin films deposited on (001)-oriented SrTiO3 substrates by radio frequency (RF) magnetron sputtering. The tetragonal axis of the films grown up to a 35 nm thickness is perpendicular to the film surface and the basal lattice parameters are imposed by the cubic structure of the substrate. Furthermore, the emergence of a spontaneous electric polarization below ~32 K points to the stabilization of an improper ferroelectric phase at low temperatures, which is not observed in bulk GdMnO3. This work shows how strain engineering can be used to tailor the structure and properties of strongly correlated oxides.
Highlights
Strain engineering has been an interesting way to control the physical properties of materials at the nanoscale level, such as thin films that can withstand tensile or shear stresses up to a significant fraction of their ideal strength[1,2,3]
When an applied magnetic field is applied along the a-axis, the temperature range of stability of the ferroelectric phase increases up to 15 K, stabilizing a commensurate magnetic
A stabilization of an ac-plane spiral spin order below 105 K was proposed to explain the stabilization of the ferroelectric phase and a nano-scale twin-like domain structure was appointed as essential for the rather high temperature ferroelectric and ferromagnetic phases observed in the orthorhombic GMO films[17]
Summary
In order to disentangle the underlying processes that can be associated with the emergence of the anomaly observed at T1, we have studied the polar properties of the tetragonal GMO thin film For this purpose, we have measured the thermally stimulated depolarizing current (TSDC) in heating runs, at fixed temperature rate of 8 K/ min, in two distinct poling conditions: the sample was cooled i) in the absence of an electric field, and ii) under different bias electric fields: 1.0; 2.5; and 5.0 kV/m. In order to determine the temperature dependence of the in-plane component of the electric polarization associated with the ferroelectric phase, we have carried out the time integration of the pyroelectric current from Fig. 4(b) that was measured at the lowest electric poling field, in order to avoid induced contributions expected from applying higher poling fields In this case, the in-plane component of the electric polarization value around 40 nC.cm−2 is obtained below 32 K, of similar order of the saturation values found in bulk TbMnO3 and DyMnO3 below 20 K9. This work provides a guide, through strain engineering, to unravel new and unexpected phases in perovskite thin films
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