Magnetoelastic-magnetoelectric phase transitions in multiferroic BiFeO3

TL;DR

This study identifies four phase transitions in multiferroic BiFeO3 below room temperature, revealing complex magnetoelastic and magnetoelectric couplings with distinct magnetic and elastic characteristics.

Contribution

It provides detailed experimental evidence of multiple low-temperature phase transitions in BiFeO3 and clarifies their magnetic, elastic, and dielectric nature, highlighting novel magnetoelastic interactions.

Findings

Four phase transitions below room temperature in BiFeO3

Strong elastic coupling at 230K transition

Magnetic transition at 50K with magnetostrictive effects

Abstract

Our measured dielectric constant and mechanical response of multiferroic BiFeO3 indicate four phase transitions below room temperature. Features correlate with those reported at 50K (from a peak in the zero-field-cooled magnetic susceptibility) and 230K (from splitting between field-cooled and zero-field-cooled magnetic data[1], and 200K (from magnon light scattering cross sections[2]). The primary order parameter is not the polarization in any of the low-T transitions. Instead, the transition near 230 K shows strong elastic coupling, while that at 50K is fundamentally magnetic, but magnetostrictively coupled to the the lattice. The low-T phase transitions display glassy behaviour. A further anomaly at 140K interpreted as spin reorientation[2,3] shows only weakly in dielectric and mechanical studies, indicating that it is predominantly magnetic with little coupling to any of the other order parameters.