Hexagonal Sr0.6Ba0.4MnO3: Spin and dipole coupling via local structure

Abstract Hexagonal Sr 0.6 Ba 0.4 MnO 3 (SBMO) follows P 6 3 / mmc symmetry where MnO 6 octahedra are both face-shared (Mn 2 O 9 bioctahedra) and corner-shared via oxygen anion. It undergoes ferroelectric (FE) and antiferromagnetic (AFM) orderings close to the room temperature. Magnetic properties appear to be governed by intricate exchange interactions among Mn 4+ ions within and in adjacent Mn 2 O 9 bioctahedra, contingent upon the local structural changes. Calculations based on our model spin-Hamiltonian reveal that the dominant linear AFM fluctuations between the Mn 4+ ions of two oxygen-linked bi-octahedra result in short range correlations, manifest as a smooth drop in magnetization below 325 K. Competition between spin-exchange and local-strain is reckoned as responsible for the atypical magneto-electricity, obtained near the room temperature.