Structural and magnetic properties of Gd³⁺ ion substituted magnesium ferrite nanopowders

Nanocrystalline MgGd_xFe_2−xO₄ powders (where x=0, 0.05, 0.1, 0.2, 0.25, 0.3) have been synthesized by the ethylene diamine tetraacetic acid (EDTA)-based sol–gel combustion method. X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, high resolution transmission electron microscopy (HRTEM) and vibrating sample magnetometer (VSM) were applied in order to study the effect of variation of Gd³⁺ ion substitution and its impact on crystal structure, crystallite size, lattice parameters, nanostructure and magnetic properties of the formed powders. XRD indicated that, after doping and calcination at 400 °C for 2 h, all samples have two spinel ferrite structures namely cubic and tetragonal phases, which are dependent on Gd³⁺ ion concentration. The cubic phase is found to increase with increasing the Gd³⁺ ion molar ratio up to 0.1, compared to pure MgFe₂O₄ and higher Gd³⁺ content samples. Indeed, with increasing Gd³⁺ ion, the crystallite size was almost unchanged whereas the lattice parameter was found to increase. FT-IR spectrum showed broadening of the ν₂ band and the presence of another band in the range (465–470 cm⁻¹) upon adding Gd³⁺ ion, which confirm the presence of Gd³⁺ ion in addition to Fe³⁺ ion at octahedral site. Besides, these bands were assigned to the formation of (Gd³⁺–O²⁻) complexes at B-sites. HRTEM images showed that the studied samples consist of nanocrystallites having average particle sizes around 9 nm for pure MgFe₂O₄ up to 27 and 42 nm for the Gd³⁺ ion substituted MgFe₂O₄ of molar ratio 0.05 and 0.30, respectively. An examination of the magnetic properties revealed an increase in saturation magnetization with increasing Gd concentration incorporation up to x=0.1, as a result of the change of cubic and tetragonal spinel ratio and lattice parameters. Meanwhile, the formed powders exhibited superparamagnetic characteristics. Therefore, such newly synthesized superparamagnetic nanoparticles, containing Gd³⁺ ion can be considered as a promising candidate for use in several potential applications including neutron capture therapy (NCT), magnetic hyperthermia, ferrofluids and magnetic resonance imaging (MRI). - Highlights: • MgGd_xFe_2−xO₄ nanoparticles are synthesized at low temperature 400 °C. • The microstructure is dependent on Gd³⁺ ion concentration. • The spinel cubic structure increases with Gd³⁺ ion up to 10%. • The nanoparticles exhibited superparamagnetic behavior at room temperature. • The anomalous behavior of M_s is due to the different magnetic moment of Fe and Gd