Temperature driven Mott-Hubbard to charge-transfer insulator transition in hexagonal Sr0.6Ba0.4MnO3

We have probed the electronic structure across the ferroelectric transition temperature (T-C = 355K) of hexagonal Sr0.6Ba0.4MnO3 (SBMO) which shows a magneto-electric effect at room temperature. The valence and conduction bands are characterized by resonant photoemission and X-ray absorption spectroscopy measurements, respectively. The valence band spectrum is found to be hugely modified across T-C. Above T-C, SBMO behaves like a Mott-Hubbard insulator, whereas at 300K, it shows a charge-transfer-type insulator behavior. Modulation in the hybridization of Mn-3d and O-2p orbitals due to local structural variations with temperature unravels the rational for the observed electronic structure transition vis a vis magnetic and electrical behaviors of SBMO.