An antisite defect mechanism for room temperature ferroelectricity in orthoferrites

TL;DR

This paper uncovers a defect-based mechanism for room temperature ferroelectricity in orthoferrites, demonstrating how antisite defects induce non-centrosymmetric distortions that enable ferroelectricity and magnetoelectric coupling in these magnetic oxides.

Contribution

It introduces an antisite defect mechanism for ferroelectricity in orthoferrites, supported by experimental and theoretical evidence, expanding the understanding of multiferroic behavior in magnetic oxides.

Findings

Antisite defects facilitate non-centrosymmetric distortions promoting ferroelectricity.

Room temperature ferroelectricity observed in YFeO3 thin films and nanocomposites.

Strain-mediated magnetoelectric coupling demonstrated in composite structures.

Abstract

Single-phase multiferroic materials that allow the coexistence of ferroelectric and magnetic ordering above room temperature are highly desirable, motivating an ongoing search for mechanisms for unconventional ferroelectricity in magnetic oxides. Here, we report an antisite defect mechanism for room temperature ferroelectricity in epitaxial thin films of yttrium orthoferrite, YFeO3, a perovskite-structured canted antiferromagnet. A combination of piezoresponse force microscopy, atomically resolved elemental mapping with aberration corrected scanning transmission electron microscopy and density functional theory calculations reveals that the presence of YFe antisite defects facilitates a non-centrosymmetric distortion promoting ferroelectricity. This mechanism is predicted to work analogously for other rare earth orthoferrites, with a dependence of the polarization on the radius of the rare earth cation. Furthermore, a vertically aligned nanocomposite consisting of pillars of a magnetoelastic oxide CoFe2O4 embedded epitaxially in the YFeO3 matrix exhibits both robust ferroelectricity and ferrimagnetism at room temperature, as well as a noticeable strain-mediated magnetoelectric coupling effect. Our work uncovers the distinctive role of antisite defects in providing a novel mechanism for ferroelectricity in a range of magnetic orthoferrites and further augments the functionality of this family of complex oxides for multiferroic applications.