A-site driven ferroelectricity in strained ferromagnetic L2NiMnO6 thin films

TL;DR

This study demonstrates that epitaxial strain induces A-site driven ferroelectricity in ferromagnetic La2NiMnO6 thin films through lattice distortions and A-site displacements, combining experimental and theoretical insights.

Contribution

It reveals a novel mechanism of ferroelectricity driven by A-site displacements in strained La2NiMnO6, supported by structural analysis and density functional theory calculations.

Findings

Epitaxial strain causes lattice stretching along [111] in La2NiMnO6.

A-site La ion displacement stabilizes ferroelectric polarization.

Ferroelectricity appears only in the rhombohedral phase with inhibited octahedral tilting.

Abstract

We report on theoretical and experimental investigation of A-site driven ferroelectricity in ferromagnetic La2NiMnO6 thin films grown on SrTiO3 substrates. Structural analysis and density functional theory calculations show that epitaxial strain stretches the rhombohedral La2NiMnO6 crystal lattice along the [111]cubic direction, triggering a displacement of the A-site La ions in the double perovskite lattice. The lattice distortion and the A-site displacements stabilize a ferroelectric polar state in ferromagnetic La2NiMnO6 crystals. The ferroelectric state only appears in the rhombohedral La2NiMnO6 phase, where MnO6 and NiO6 octahedral tilting is inhibited by the 3-fold crystal symmetry. Electron localization mapping showed that covalent bonding with oxygen and 6s orbital lone pair formation are negligible in this material.