Eu-Mn Charge Transfer and the Strong Charge-Spin-Electronic Coupling Behavior in EuMnO.

Based on first-principles calculations with the DFT + method, the couplings of lattice, charge, spin, and electronic behaviors underlying the Eu-Mn charge transfer in a strongly correlated system of EuMnO were investigated. The potential valence transition from Eu/Mn to Eu/Mn was observed in a compressed lattice with little distortions, which is achieved under hydrostatic pressure and external strain. The intraplane antiferromagnetism (AFM) of Mn is proved to be instrumental in the emergence of Eu. Furthermore, we calculated the magnetic exchange interactions within two equilibrium structures of EuMnO and EuMnO. Mn-Mn ferromagnetic exchange in the -plane is enhanced strongly in the EuMnO structure, contributing to the existence of mixed states. The versatile electronic structures were obtained within the EuMnO phase by imposing different magnetic configurations on the Eu and Mn sublattice, attributed to the coupling of charge transfer and magnetic orderings. It is found that the intraplane ferromagnetic ordering of Mn leads to a metallic electronic structure with the coexistence of Eu and Eu, while the intraplane AFM Mn spin ordering leads to insulating states only with Eu. Notably, a half-metallic characteristic emerges at the magnetic ground state of CF ordering (C-type AFM for the Eu sublattice and ferromagnetic for the Mn sublattice), which makes such a supposed phase more intriguing than the conventional experimental phase. Additionally, the mixture of delocalized 4f with 5d states of Eu in the background of Mn 3d and O 2p orbitals implies a pathway of Eu 4f 5d ↔ O 2p ↔ Mn 3d for charge transfer between Eu and Mn. Our calculation shows that the Eu-Mn charge transfer could be expected in compressed EuMnO and the introduction of Eu 4f states near the Fermi level plays an important role in manipulating the interlinks of charge and spin together with electronic behaviors.