Partial molecular orbitals in face-sharing 3d manganese trimer: Comparative studies on Ba4TaMn3O12 and Ba4NbMn3O12

Abstract

We present a molecular orbital candidate Ba4TaMn3O12 with a face-sharing octahedra trimer, by comparing it with a related compound Ba4NbMn3O12. The synthesis of the polycrystalline powder is optimized by suppressing the secondary impurity phase via x-ray diffraction. Magnetic susceptibility measurements on the optimized samples reveal a weak magnetic hysteresis with magnetic transitions consistent with heat capacity results. The effective magnetic moments from susceptibility indicate a strongly coupled S=2 antiferromagnetic trimer at around room temperature, whereas the estimated magnetic entropy from heat capacity suggests the localized S=3/2 timer. These results can be explainable by a partial molecular orbital state, in which three t2g electrons are localized in each Mn ion and one eg electron is delocalized over two-end Mn ions of the trimer based on density functional theory calculations. This unconventional 3d orbital state is comprehended as a consequence of competition between the hybrid interatomic orbitals within the Mn trimer and the local moment formation by on-site Coulomb correlations. Published by the American Physical Society 2024