Ferromagnetism in nanoscale BiFeO3

Abstract

A remarkably high saturation magnetization of ~0.4µB/Fe along with room temperature ferromagnetic hysteresis loop has been observed in nanoscale (4–40 nm) multiferroic BiFeO3 which in bulk form exhibits weak magnetization (~0.02µB/Fe) and an antiferromagnetic order. The magnetic hysteresis loops exhibit exchange bias and vertical asymmetry which could be because of spin pinning at the boundaries between ferromagnetic and antiferromagnetic domains. Interestingly, both the calorimetric and dielectric permittivity data in nanoscale BiFeO3 exhibit characteristic features at the magnetic transition point. These features establish the formation of a true ferromagnetic-ferroelectric system with a coupling between the respective order parameters in nanoscale BiFeO3.