# Origin and tuning of room-temperature multiferroicity in Fe doped BaTiO$_3$

## TL;DR

This study explores the origin of room-temperature multiferroicity in Fe-doped BaTiO$_3$, revealing it as a mixed-phase material with ferromagnetism from hexagonal and ferroelectricity from tetragonal phases, controlled by ionic size, Jahn-Teller distortions, and oxygen vacancies.

## Contribution

It identifies key factors influencing phase stability in Fe-doped BaTiO$_3$ and demonstrates how to control them to enhance multiferroic properties at room temperature.

## Key findings

- Fe-doped BaTiO$_3$ exhibits mixed-phase multiferroicity at room temperature.
- Hexagonal phase contributes ferromagnetism, tetragonal phase contributes ferroelectricity.
- Ionic size, Jahn-Teller distortions, and oxygen vacancies are key to phase stability.

## Abstract

Simultaneous co-existence of room-temperature(T) ferromagnetism and ferroelectricity in Fe doped BaTiO$_3$ (BTO) is intriguing, as such Fe doping into tetragonal BTO, a room-T ferroelectric (FE), results in the stabilization of its hexagonal polymorph which is FE only below $\sim$80K. Here, we investigate its origin and show that Fe-doped BTO has a mixed-phase room-temperature multiferroicity, where the ferromagnetism comes from the majority hexagonal phase and a minority tetragonal phase gives rise to the observed weak ferroelectricity. In order to achieve majority tetragonal phase (responsible for room-T ferroelectricity) in Fe-doped BTO, we investigate the role of different parameters which primarily control the PE hexagonal phase stability over the FE tetragonal one and identify three major factors namely, the effect of ionic size, Jahn-Teller (J-T) distortions and oxygen vacancies (OVs), to be primarily responsible. The effect of ionic size which can be qualitatively represented using the Goldschmidt's tolerance (GT) factor seems to be the major dictating factor for the hexagonal phase stability. The understanding of these factors not only enables us to control them but also, achieve suitable co-doped BTO compound with enhanced room-T multiferroic properties.