Anisotropic orbital occupation and Jahn-Teller distortion of orthorhombic YMnO3 epitaxial films: A combined experimental and theoretical study on polarization-dependent x-ray absorption spectroscopy

The b-axis oriented orthorhombic YMnO3 (o-YMnO3) epitaxial films on a YAlO3 (010) substrate were fabricated with pulsed-laser deposition. The anisotropic orbital occupation and Jahn-Teller (JT) distortion of an o-YMnO3 film were investigated with polarization-dependent x-ray absorption spectra and configuration-interaction multiplet-cluster calculations. A significant energy difference, ∼3.8 eV, for the main white line along E//b and E//a in polarization-dependent Mn K-edge spectra of o-YMnO3 indicates an extraordinary JT distortion and significant anisotropic Mn–O bonding within the ab plane in the o-YMnO3 film. Most importantly, although the orbital occupation of 3d electrons in o-YMnO3 films is almost the same as that in single crystalline o-DyMnO3, the JT distortion of o-YMnO3 films is larger than that of single crystalline o-DyMnO3, deduced from the multiplet calculations. We speculate that this JT distortion predominantly contributes to the origin of the cycloidal spin deformation in bulk o-YMnO3, because of a suppressed nearest-neighbor superexchange interaction and an enhanced next-nearest-neighbor superexchange interaction. These complementary results provide insight into the origin of the E-type magnetic configuration of o-YMnO3.