Magnetic properties of BiMnO3 nanoparticles in SBA-15 mesoporous silica

Nanoparticles of multiferroic material BiMnO3 were synthesized in the pores of the mesoporous silica SBA-15 and their magnetic properties were investigated. The powder X-ray diffraction pattern for the nanoparticles at room temperature was similar to that for bulk crystals with monoclinic symmetry. The particle size of the nanocrystals was estimated to be about 14 nm using Scherrer's equation. The temperature dependence of the DC susceptibilities for the nanoparticles showed superparamagnetic behavior. The susceptibility and thermoremanent magnetization exhibited the ferromagnetic feature and the ferromagnetic transition temperature was almost same to that for bulk crystals, ∼ 100 K. However, the Weiss temperature Θ was evaluated as the negative value and the magnetization curve showed antiferromagnetic behavior. The results suggest the antiferromagnetic properties appeared prominently in the nanoparticles.