Tailoring polar domains in Sr1-xBaxMnO3-δ epitaxial thin films

An exciting family of multiferroics is AMnO3 (A= Ca, Sr, Ba) perovskite, which gives rise to ferroelectricity driven by the off-centring of the magnetic cation Mn⁴⁺ upon subtle changes in stoichiometry and crystal symmetry[1]. A good example is the antiferromagnetic Sr_1-xBa_xMnO_3-δ (SBMO), a metastable perovskite that turns into ferroelectric for x > 0.4 [2].

In this work, we have synthesized SBMO (0 ≤ x ≤ 0.5) epitaxial films on single crystalline LSAT (001) substrates by pulsed laser deposition, and investigated the dependence of their polar states on strain and stoichiometry (i.e. Ba content and oxygen vacancies). X-ray diffraction has allowed us to determine the crystal structure, orientation, and strain state of the films. Scanning transmission electron microscopy (STEM) [3] has been used to unravel the local polarization on the atomic level that arises from the relative displacements of the Mn and O sublattices. Polarization is intimately linked to the sign and magnitude of epitaxial strain and can be tuned either in-plane or out-of-plane with respect to the substrate plane (see Figure 1), by the appropriate choice of the substrate-induced strain, Ba doping and the O content induced by controlled annealing [4].

[1] H. An et al., NPG Asia Materials 13, 69 (2021)

[2] H Sakai et al, Phys. Rev. Lett. 107 (2011)

[3] R. Guzman et al., Nano Letters 16 , 2221–2227 (2016)

[4] P. Koutsogiannis, P. A. Algarabel, J. A. Pardo and C. Magén, in preparation (2022)