Epitaxial Stabilization of the Perovskite Phase in (Sr_1–xBa_x)MnO₃ Thin Films

Abstract

A novel mechanism of ferroelectricity driven by off-centering magnetic Mn(4+) ions was proposed in (Sr1-xBax)MnO3, in its ideal perovskite phase, which yields enormous expectations in the search for strong magnetoelectric materials. Still, the desired perovskite phase has never been stabilized in thin films due to its extremely metastable character. Here, we report on a thorough study of the perovskite phase stabilization of (Sr1-xBax)MnO3 thin films, 0.2 ≤ x ≤ 0.5, grown by pulsed laser deposition onto (001)-oriented perovskite substrates. X-ray diffraction measurements and scanning transmission electron microscopy reveal that, under appropriate deposition conditions, the perovskite phase is fully stabilized over the nonferroelectric hexagonal phase, despite the latter being increasingly favored on increasing Ba-content. Moreover, we have managed to grow epitaxial coherent cube-on-cube (Sr1-xBax)MnO3 films upon strains ranging from 0% to 4%. Our results become a milestone in further studying perovskite (Sr1-xBax)MnO3 thin films and pave the way for tailoring ferroic and magnetoelectric properties either by strain engineering or Ba-doping.

Polar-Graded Multiferroic SrMnO3 Thin Films

“…19 . Here, the oxygen-pressure dependence on the perovskite phase stabilization is the direct evidence that the formation of oxygen vacancies during thin film growth plays a central role in its stability, since perovskite SMO is only stabilized under low oxygen pressure 28,36,37 . The formation of oxygen vacancies is charge compensated by a reduction of the formal oxidation state of some Mn 4+ to Mn 3+ , resulting in a chemical expansion of the crystal lattice, relieving the strain.…”

“…1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 8 Earlier works in ferroelectric HoMnO 3 epitaxial films pointed out the interplay between strain gradients and the presence of oxygen vacancies and the possibility to modulate the strain gradients, and thus flexoelectricity and polarization, as a function of the oxygen pressure during the film growth 19 . Here, the oxygen-pressure dependence on the perovskite phase stabilization is the direct evidence that the formation of oxygen vacancies during thin film growth plays a central role in its stability, since perovskite SMO is only stabilized under low oxygen pressure 28,36,37 . The formation of oxygen vacancies is charge compensated by a reduction of the formal oxidation state of some Mn 4+ to Mn 3+ , resulting in a chemical expansion of the crystal lattice, relieving the strain.…”

Spin-phonon coupling in epitaxialSr0.6Ba0.4MnO3thin films

“…Note that bulk SB40MO is perfectly cubic [7]. A deeper discussion regarding the structure of strained Sr 1−x Ba x MnO 3 thin films can be found elsewhere [11].…”

“…The structural characterization of the films was carried out by x-ray diffraction (XRD) with a Bruker D8 Advance high-resolution diffractometer. The sample growth, perovskite phase stability, and structure of Sr 1−x Ba x MnO 3 films were reported elsewhere [11].…”

“…Sr 1−x Ba x MnO 3 films were stabilized in the pseudocubic perovskite phase over the hexagonal ground state through epitaxial growth of coherent films on different lattice-parameter substrates [11]. In this work we will focus on epitaxially strained Sr 0.6 Ba 0.4 MnO 3 (SB40MO) thin films deposited on (001)-oriented LSAT substrates, which yield a slight tetragonal distortion [11], contrasting with the perfectly cubic structure of bulk specimens [7]. Importantly enough, we will demonstrate that SB40MO/LSAT films show strong spin-phonon coupling near T N , proving the magnetoelectric coupling effect in perovskite Sr 1−x Ba x MnO 3 epitaxial thin films.…”