Effect of Jahn-Teller distortion on the magnetic characteristics of orthorhombic YMnO₃ thin films

The local strain on the MnO₆ octahedra in perovskite multiferroic manganite has been found to impose various intriguing effects on orbital and magnetic ordering texture, which is the key to the magnetoelectric coupling giving rise to the eventual multiferroicity. In this study, we deliberately grew the orthorhombic YMnO₃ (o-YMO) thin films on SrTiO₃(100) and SrTiO₃(110) single crystal substrates by pulsed laser deposition (PLD) to manipulate the lattice strain along specific crystallographic orientations. The crystal structure and relevant lattice strain of the thin films were characterized by X-ray scattering, including θ-2θ and Φ-scans, and reciprocal space mapping (RSM). Moreover, the measured Mn L_2,3-edge X-ray absorption spectroscopy (XAS) spectra were rigorously compared with the theoretically calculated ones, which evidently exhibited two distinctly different orbital ordering textures for o-YMO films grown on different SrTiO₃ substrates. The shift of Mn d-orbital degeneracy is expected to result in significant effect on the magnetic properties of the thin films. Indeed, the temperature dependent susceptibility χ(T) showed evidence of coexistence of the E-type and cycloidal antiferromagnetic ordering in the temperature range of 30-40 K in both films with, nevertheless, very different and complicated associated M-H hysteresis loops, which were also very much dependent on the direction of the applied field with respect to crystallographic orientations.