Origin of Magnetization in Silica-coated Fe3O4 Nanoparticles Revealed by Soft X-ray Magnetic Circular Dichroism

Abstract

Magnetite (Fe3O4) nanoparticles (NPs) and SiO2-coated Fe3O4 nanoparticles have successfully been synthesized using co-precipitation and modified Stöber methods, respectively. The samples were characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, high-resolution transmission electron microscopy (HRTEM), vibrating sample magnetometer (VSM) techniques, X-ray absorption spectroscopy (XAS), and X-ray magnetic circular dichroism (XMCD). XRD and FTIR data confirmed the structural configuration of a single-phase Fe3O4 and the successful formation of SiO2-coated Fe3O4 NPs. XRD also confirmed that we have succeeded to synthesize nano-meter size of Fe3O4 NPs. HRTEM images showed the increasing thickness of SiO2-coated Fe3O4 with the addition of the Tetraethyl Orthosilicate (TEOS). Room temperature VSM analysis showed the magnetic behaviour of Fe3O4 and its variations that occurred after SiO2 coating. The magnetic behaviour is further authenticated by XAS spectra analysis which cleared about the existence of SiO2 shells that have transformed the crystal as well as the local structures of the magnetite NPs. We have performed XMCD measurements, which is a powerful element-specific technique to find out the origin of magnetization in SiO2-coated Fe3O4 NPs, that verified a decrease in magnetization with increasing thickness of the SiO2 coating.Graphical Magnetite (Fe3O4) nanoparticles (NPs) and SiO2-coated Fe3O4 nanoparticles have successfully been synthesized using co-precipitation and modified Stöber methods, respectively. The samples were characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, high-resolution transmission electron microscopy (HRTEM), vibrating sample magnetometer (VSM) techniques, X-ray absorption spectroscopy (XAS), and X-ray magnetic circular dichroism (XMCD). XRD and FTIR data confirmed the structural configuration of a single-phase Fe3O4 and the successful formation of SiO2-coated Fe3O4 NPs. XRD also confirmed that we have succeeded to synthesize nano-meter size of Fe3O4 NPs. HRTEM images showed the increasing thickness of SiO2-coated Fe3O4 with the addition of the Tetraethyl Orthosilicate (TEOS). Room temperature VSM analysis showed the magnetic behaviour of Fe3O4 and its variations that occurred after SiO2 coating. The magnetic behaviour is further authenticated by XAS spectra analysis which cleared about the existence of SiO2 shells that have transformed the crystal as well as the local structures of the magnetite NPs. We have performed XMCD measurements, which is a powerful element-specific technique to find out the origin of magnetization in SiO2-coated Fe3O4 NPs, that verified a decrease in magnetization with increasing thickness of the SiO2 coating.