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

• Published in: Journal of alloys and compounds 2019-08, Vol.796, p.237-242
• Main Authors: Rawat, Ritu, Choudhary, R.J., Awasthi, A.M., Sagdeo, Archna, Sinha, A.K., Raghunathan, Rajamani, Sathe, V.G., Phase, D.M.
• Format: Article
• Language: English
• Subjects: Antiferromagnetic; Antiferromagnetism; Dipole interactions; Ferroelectric; Ferroelectric materials; Ferroelectricity; Magnetic properties; Magnetism; Magneto-electric; Manganese ions; Variation
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2019.05.003

Hexagonal Sr0.6Ba0.4MnO3 (SBMO) follows P63/mmc symmetry where MnO6 octahedra are both face-shared (Mn2O9 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 Mn4+ ions within and in adjacent Mn2O9 bioctahedra, contingent upon the local structural changes. Calculations based on our model spin-Hamiltonian reveal that the dominant linear AFM fluctuations between the Mn4+ 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. •An incipient ferroelectric (FE) with magnetic anomaly nearby room temperature.•Improper-FE is owed to the locally-unequal Mn–O bond lengths in the MnO6 octahedra.•Short range stabilization of dipoles with short range magnetic ordering.•Mn-displacement soft-vibration mode is coupled to the spin ordering in the material.•Frustration involving spin-exchange and local-strain is responsible for the ME.