Rotomagnetic coupling in fine grained multiferroic BiFeO3: Theory and experiment

TL;DR

This study combines theoretical LGD modeling and experiments to reveal a size-induced increase in the AFM transition temperature in BiFeO3 ceramics, driven by rotomagnetic and magnetostrictive couplings.

Contribution

It provides the first experimental validation of size effects on AFM transition temperature in BiFeO3 and highlights the dominant role of rotostriction in controlling magnetic states.

Findings

AFM transition temperature increased to 690 K in ceramics

Strong size-induced effects due to rotomagnetic coupling

Rotostriction identified as the dominant coupling mechanism

Abstract

Using Landau-Ginzburg-Devonshire (LGD) theory for BiFeO3 dense fine grained ceramics with quasi spherical grains and nanosized inter grain spaces enriched by elastic defects, we calculated a surprisingly strong size-induced increase of the AFM temperature caused by the joint action of rotomagnetic and magnetostrictive coupling. Notably that all parameters included in the LGD functional have been extracted from experiments, not assumed. Complementary we performed experiments for dense BiFeO3 ceramics, which revealed that the shift of antiferromagnetic transition to 690 K instead of 645 K for a single crystal. To explain theoretically the result, we consider the possibility to control antiferromagnetic state of multiferroic BiFeO3 via biquadratic antiferrodistortive rotomagnetic, rotoelectric, magnetostrictive and magnetoelectric couplings. According to our calculations the highest is the rotostriction contribution, the magnetostrictive and electrostriction contributions appeared smaller.