Abstract
The evolution of lattice strain on crystallographic domain structures and magnetic properties of epitaxial low-bandwidth manganite Gd0.6Ca0.4MnO3 (GCMO) films have been studied with films on different substrates: SrTiO3, (LaAlO3)0.3(Sr2AlTaO6)0.7, SrLaAlO3, and MgO. The X-ray diffraction data reveals that all of the films, except the films on MgO, are epitaxial and have an orthorhombic structure. Cross-sectional transmission electron microscopy (TEM) shows lattice mismatch-dependent microstructural defects. Large-enough tensile strain can increase oxygen vacancies concentration near the interface and can induce vacancies in the substrate. In addition, a second phase was observed in the films with tensile strain. However, compressive strain causes dislocations in the interface and a mosaic domain structure. On the other hand, the magnetic properties of the films, including saturation magnetization, coercive field, and transport property depend systematically on the substrate-induced strain. Based on these results, the choice of appropriate substrate is an important key to obtaining high-quality GCMO film, which can affect the functionality of potential device applications.
Highlights
The epitaxial GCMO films were grown on SrTiO3 (STO), (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT), SrLaAlO3 (SLAO), and MgO substrates by pulsed laser deposition (PLD)
The lattice mismatch between the GCMO bulk and diagonal of all substrate is determined by the formula f = (√2aS − aB)/ aB, where aB = 5.424 Å is the average of GCMO bulk values in the in-plane direction.[21]
The epitaxial GCMO films were grown by pulsed laser deposition (PLD) with 2000 pulses of XeCl-laser (λ = 308 nm) with the energy density of 1.3 J/cm[2] and frequency of 5
Summary
The mixed-valence A1−xBxMnO3 perovskite manganites, where A and B are rare-earth and divalent alkaline elements, have recently become the focus of extensive research due to their unusual magnetic and magnetoresistance properties.[1−4]Among the perovskites, the low-bandwidth manganites, such as Pr1−xCaxMnO3 (PCMO) and Gd1−xCaxMnO3 (GCMO), are interesting due to the stable charge ordering (CO) state in the whole doping range, leading to several important features like resistive switching and spin memory effect.[5−8] the Gd-based low-bandwidth perovskites show the CO state near room temperature and exhibit specific magnetic features, the reversal magnetization at low temperature and in the applied magnetic field, leading to a ferrimagnetic ground state.[9−12] The structural and physical properties of such materials are strongly dependent on the deposition technique and the lattice mismatch with the substrate, which results in uniaxial strain.[13−15] The strain can be responsible for phase separation[16,17] and modification of the relation between the lattice parameters in the direction perpendicular to growth (c) and the one in the parallel plane (a).[18]. In our previous paper,[20] positron annihilation studies of Gd0.6Ca0.4MnO3 (GCMO) thin films grown on SrTiO3 (STO) showed that most of the oxygen vacancies and open volume defects are in the interface region between the film and the substrate. This is due to the transfer of oxygen from STO to the film bulk to compensate oxygen vacancies in the GCMO lattice. The high-quality Gd0.6Ca0.4MnO3 thin films have been deposited on different substrates, and their microstructural, magnetic, and electrical properties have been investigated These results show the effect of lattice mismatch and pave the way for integrating GCMO films on silicon, which is the ultimate goal
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