Ground-state structure, orbital ordering and metal-insulator transition in double-perovskite PrBaMn2O6

In recent years, A-site ordered half-doped double-perovskite manganites RBaMn2O6 (R=rare earth) have attracted much attention due to their remarkable physical properties and a prospect of application as magnetoresistive, multiferroic, and oxygen storage materials. The nature of the ground state in RBaMn2O6 as well as sequence of phase transitions taking place at cooling are not yet well understood due to complexity in both experimental and theoretical studies. Here we address the origin of the ground-state structure in PrBaMn2O6 as well as its electronic and magnetic properties. Utilizing GGA+U approach and specially designed strategy to perform structural optimization, we show that the system has two competing AFM-A and AFM-CE magnetic structures with very close energies. The AFM-A structure is a metal, while AFM-CE is an insulator and the transition to the insulating state is accompanied by the charge Mn3+/Mn4+, and orbital 3x(2) - r(2)/3y(2) - r(2) orderings. This orbital ordering results in strong cooperative Jahn-Teller (JT) distortions, which lower the crystal symmetry. Our findings give a key to understanding contradictions in available experimental data on PrBaMn2O6 and open up the prospects to theoretical refinements of ground state structures in other RBaMn2O6 compounds. (c) 2022 Elsevier B.V. All rights reserved.