Ferromagnetism in nanoscale BiFeO3

TL;DR

This paper reports the discovery of room temperature ferromagnetism in nanoscale BiFeO3, showing enhanced magnetic properties and coupling between magnetic and ferroelectric orders, unlike its bulk form.

Contribution

It demonstrates that nanoscale BiFeO3 exhibits significant ferromagnetism and coupling effects, contrasting with its weak magnetization in bulk form, revealing new multiferroic behavior at the nanoscale.

Findings

High saturation magnetization (~0.4μ_B/Fe) in nanoscale BiFeO3

Presence of exchange bias and vertical asymmetry in hysteresis loops

Characteristic features at magnetic transition point indicating coupling

Abstract

A remarkably high saturation magnetization of ~0.4mu_B/Fe along with room temperature ferromagnetic hysteresis loop has been observed in nanoscale (4-40 nm) multiferroic BiFeO_3 which in bulk form exhibits weak magnetization (~0.02mu_B/Fe) and an antiferromagnetic order. The magnetic hysteresis loops, however, exhibit exchange bias as well as vertical asymmetry which could be because of spin pinning at the boundaries between ferromagnetic and antiferromagnetic domains. Interestingly, like in bulk BiFeO_3, both the calorimetric and dielectric permittivity data in nanoscale BiFeO_3 exhibit characteristic features at the magnetic transition point. These features establish formation of a true ferromagnetic-ferroelectric system with a coupling between the respective order parameters in nanoscale BiFeO_3.