Microwave-assisted combustion synthesis of soft ferromagnetic spinel MFe2O4 (M = Ni, Mg, Zn) nanoparticles using Citrus limon fruit extract as a fuel

We report the preparation of soft ferromagnetic spinel MFe2O4 (M = Ni, Mg, Zn) nanoparticles via microwave-assisted combustion synthesis using Citrus limon fruit extract as a fuel. XRD, FTIR, Raman, and EDX studies revealed that phase pure polycrystalline NiFe2O4, MgFe2O4, and ZnFe2O4 having cubic structure were formed when we introduce the desired divalent metal ion during the synthesis. TEM analysis clearly shows that NiFe2O4 and MgFe2O4 samples have spherical shape nanoparticles, while the ZnFe2O4 sample has cube-like nanoparticles with different size distributions. The average size of NiFe2O4, MgFe2O4, and ZnFe2O4 nanoparticles was found to be 10 ± 3 nm, 20 ± 2 nm, and 25 ± 4 nm, respectively. We believe that citrate present in Citrus limon fruit extract and nitrate ions that exist in the reaction medium can act as reductant/oxidant leads to auto-combustion and form crystallized MFe2O4 nanoparticles without further high-temperature calcination. From VSM analysis, the saturation magnetization for NiFe2O4, MgFe2O4, and ZnFe2O4 was found as 10.16 emu/g, 8.69 emu/g, and 4.23 emu/g, respectively. The different saturation magnetization of the MFe2O4 nanoparticles has a strong correlation with the magnetic moment of divalent cations (Ni2+, Mg2+, Zn2+), superexchange of Fe3+ ions between the tetrahedral (A) and the octahedral (B) sites as well as owing to particle size/morphology and impurities. This study offers a facile approach to obtain soft ferromagnetic spinel ferrite nanoparticles with tunable saturation magnetization which may find a wide spectrum of applications.