Structural distortion and magnetism of BiFeO3 epitaxial thin films: a Raman spectroscopy and neutron diffraction study

TL;DR

This study investigates the structure and magnetism of single-phase BiFeO3 epitaxial thin films, revealing a transition from tetragonal to monoclinic structure with increasing thickness and confirming antiferromagnetic order without cycloidal modulation.

Contribution

It provides detailed structural and magnetic characterization of BiFeO3 thin films using Raman spectroscopy and neutron diffraction, highlighting differences from bulk properties.

Findings

BiFeO3 films are tetragonal at 70 nm thickness

Films become monoclinic at 240 nm thickness

Neutron diffraction confirms G-type antiferromagnetic order

Abstract

A previous study of the growth conditions has shown that single-phase BiFeO3 thin films can only be obtained in a narrow pressure-temperature window and that these films display a weak magnetic moment. Here we study in more detail the structure and the magnetism of single-phase BiFeO3 films by means of reciprocal space mapping, Raman spectroscopy and neutron diffraction. X-ray and Raman data suggest that the BiFeO3 structure is tetragonal for 70 nm-thick films and changes to monoclinic for 240 nm-thick films, thus remaining different from that of the bulk (rhombohedral) structure. In the 240 nm monoclinically distorted film neutron diffraction experiments allow the observation of a G-type antiferromagnetic order as in bulk single crystals. However, the satellite peaks associated with the long-wavelength cycloid present in bulk BiFeO3 are not observed. The relevance of these findings for the exploitation of the magnetoelectric properties of BiFeO3 is discussed.