Double polarization hysteresis loop induced by the domain pinning by defect dipoles in HoMnO3 epitaxial thin films

TL;DR

This study reveals that defect dipoles in HoMnO3 thin films cause double polarization hysteresis loops by pinning domains, a phenomenon linked to unintentional defects like Fe1+ and oxygen vacancies formed during growth.

Contribution

It demonstrates the origin of double hysteresis loops in HoMnO3 films due to defect dipoles, highlighting the role of defect formation during film growth without aging.

Findings

Double hysteresis loops observed in HoMnO3 thin films.

Defect dipoles composed of oxygen vacancies and Fe1+ defects identified.

Domain pinning by defect dipoles causes the hysteresis behavior.

Abstract

We report on antiferroelectriclike double polarization hysteresis loops in multiferroic HoMnO3 thin films below the ferroelectric Curie temperature. This intriguing phenomenon is attributed to the domain pinning by defect dipoles which were introduced unintentionally during film growth process. Electron paramagnetic resonance suggests the existence of Fe1+ defects in thin films and first principles calculations reveal that the defect dipoles would be composed of oxygen vacancy and Fe1+ defect. We discuss migration of charged point defects during film growth process and formation of defect dipoles along ferroelectric polarization direction, based on the site preference of point defects. Due to a high-temperature low-symmetry structure of HoMnO3, aging is not required to form the defect dipoles in contrast to other ferroelectrics (e.g., BaTiO3).