Hexagonal Sr0.6Ba0.4MnO3: Spin and Dipole Coupling via Local Structure

TL;DR

This study investigates the local structural influences on spin and dipole interactions in hexagonal Sr0.6Ba0.4MnO3, revealing complex magnetic and ferroelectric behaviors near room temperature driven by local structural and exchange interactions.

Contribution

It introduces a model spin-Hamiltonian to explain the interplay of spin and dipole coupling mediated by local structural variations in SBMO.

Findings

Short-range AFM correlations below 325 K.

Magneto-electric effects near room temperature.

Intricate exchange interactions influenced by local structure.

Abstract

Hexagonal Sr0.6Ba0.4MnO3 (SBMO) follows P63/mmc symmetry where MnO6 octahedra are both face-shared (Mn2O9 bi-octahedra) 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 bi-octahedra, 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.