We have elucidated the spin, lattice, charge, and orbital coupling mechanism underlying the multiferroic character in tensile-strained EuTiO3 films. Symmetry determined by oxygen octahedral tilting shapes the hybridization between the Eu 4f and the Ti 3d orbitals, and this inhibits predicted Ti displacement proper ferroelectricity. Instead, phonon softening emerges at low temperatures within the pseudocube (110) plane, orthogonal to the anticipated ferroelectric polarization symmetry. Additionally, the magnetic anisotropy is determined by orbital distortion through hybridization between the Ti 3d and the typically isotropic Eu2+4f states. This unique scenario demonstrates the critical role symmetry plays in the coupling of order parameters defining multiferroic behavior.
Bibliographical noteFunding Information:
Work at Argonne and the use of beamline 6-ID-B at the Advanced Photon Source at Argonne was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-06CH11357. The EPSRC-funded XMaS beamline at the ESRF is directed by M. J. Cooper, C. A. Lucas, and T. P. A. Hase. We are grateful to O. Bikondoa, D. Wermeille, and L. Bouchenoire for their invaluable assistance and to S. Beaufoy and J. Kervin for additional XMaS support. The work at Cornell was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award No. DE-SC0002334. Substrate preparation was performed, in part, at the Cornell NanoScale Facility, a member of the National Nanotechnology Coordinated Infrastructure (NNCI), which is supported by the National Science Foundation (Grant No. NNCI-1542081). Use of beamline X23-A2 at the National Synchrotron Light Source was supported by the U.S. Department of Energy, Office of Basic Energy Sciences under Contract No. DE-AC02-98CH10886. Additional support was provided by the National Institute of Standards and Technology. The work at the University of Minnesota was funded by the Department of Energy through the University of Minnesota Center for Quantum Materials under Grant No. DE-SC-0016371.