Effect of A-site substitution and calcination temperature in Fe3O4 spinel ferrites

In this report, we adopted an auto-combustion method to synthesize polycrystalline magnetite (Fe3O4) and magnesium ferrites (MgFe2O4) nanoparticles. The synthesized nanoparticles were characterized using techniques such as X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM), Fourier-transform infrared spectroscopy (FTIR), Vibration sample magnetometer (VSM) and photoluminescence (PL) spectroscopy. X-ray diffraction profiles of all the synthesized nanoparticles [Fe3O4 (500 °C): FO NPs, MgFe2O4 (500 °C): MFO1 NPs and MgFe2O4 (700 °C): MFO2 NPs] confirmed phase pure crystallinity without any secondary phases such as FeO and Fe2O3, etc. The implementation of Rietveld refinement determined the cubic crystal symmetry with space group Fd3-m\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$Fd\stackrel{-}{3}m$$\end{document} for all the synthesized nanoparticles. FE-SEM micrographs depicted the pseudo-spherical morphology with an average grain size of 26.18 nm, 51.6 nm, and 69.68 nm for FO NPs, MFO1 NPs, and MFO2 NPs, respectively. FTIR spectra illustrated the appearance of peaks at 1645 cm−1 and 1345 cm−1 which attributes to metal ions (Fe3+/Mg2+). Photoluminescence spectra of synthesized nanoparticles displayed the emission wavelength in a range of 508–521 nm. The values of saturation magnetization for FO NPs, MFO1 NPs, and MFO2 NPs were found to be 34.2 emu/g, 15.3 emu/g, and 28.8 emu/g, respectively. The magnetization of MgFe2O4 nanoparticles increased with increasing calcination temperature (500–700 °C) so as the grain size. It indicated that Mg substitution at A-site of AB2O4-type (MgFe2O4) spinel ferrite not only gave the phase pure crystal structure but also compete with the magnetic properties of Fe3O4 with increasing calcination temperature. MgFe2O4 nanoparticles (calcined at 700 °C) depicted superparamagnetic behavior and can be utilized as a drug delivery agent for biomedical applications.