Ferromagnetism and Ferroelectricity in epitaxial ultra-thin BiMnO3 films

TL;DR

This study investigates the ferroelectric and ferromagnetic properties of ultra-thin BiMnO3 films, revealing room temperature ferroelectricity in pseudo-cubic films and ferromagnetism below 100 K, with structural changes at increased thickness.

Contribution

It demonstrates the coexistence of ferromagnetism and ferroelectricity in ultra-thin BiMnO3 films and links structural phases to these properties.

Findings

Room temperature ferroelectricity observed in pseudo-cubic films.

Ferromagnetism present below 100 K in all samples.

Structural transition from pseudo-cubic to monoclinic at increased thickness.

Abstract

We studied the ferroelectric and ferromagnetic properties of compressive strained and unstrained BiMnO3 thin films grown by rf-magnetron sputtering. BiMnO3 samples exhibit a 2D cube-on-cube growth mode and a pseudo-cubic struc-ture up to a thickness of 15 nm and of 25 nm when deposited on (001) SrTiO3 and (110) DyScO3, respectively. Above these thicknesses we observe a switching to a 3D island growth and a simultaneous structural change to a monoclinic structure characterized by a (00l) orientation of the monoclinic unit cell. While ferromagnetism is observed below Tc = 100 K for all samples, signatures of room temperature ferroelectricity were found only in the pseudo-cubic ultra-thin films, indicating a correlation between electronic and structural orders.