Synthesis and magneto-optical properties of triethylene glycol stabilized Mn_1−xZn_xFe₂O₄ nanoparticles

Highlights: • All products present superparamagnetic behavior at room temperature (RT). • The high M_s and magnetic moment values are attributed to cation distribution change. • The greater magnitude of band gap for the coated samples proves the existence of magnetic and nonmagnetic shells. - Abstract: In this study, thermal decomposition approach was used for the synthesis of super-paramagnetic triethylene glycol (TEG)-stabilized Mn_1−xZn_xFe₂O₄ (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) nanoparticles. The change in the magneto-optical properties of the products due to TEG stabilization were investigated. The composition, phase, magnetic and optical properties were determined by X-ray diffraction, transmission/scanning electron microscopy and vibrating sample magnetometer, UV–Vis spectrophotometer respectively. The triethylene glycol was used as both coordination and stabilizing agent. X-ray powder diffraction and Transmission electron analysis showed that all samples have narrow size distribution in the range of 8–6 nm. Room temperature VSM magnetization measurements on 3 selected NPs exhibit superparamagnetic behavior. This characteristic behavior can be generalized for all TEG-stabilized Mn_1–xZn_xFe₂O₄ NPs. Saturation magnetization (M_s) of TEG-stabilized ZnFe₂O₄ NPs is 32.90 emu/g is much greater than the bulk M_s value of 5 emu/g. This case is attributed to cation distribution change from normal spinel to mixed structure. The average crystallite size (D_mag) was estimated from the Langevin fit studies performed on M–H hysteresis loops. The obtained average D_mag values are about 6 nm and this diameter is in great accordance with the results calculated from XRD measurements. Diffuse reflectance spectroscopy was applied to determine the optical properties of samples. The optical direct band gap values of TEG-stabilized Mn_1−xZn_xFe₂O₄ NPs are minimum (2.05 eV) for MnFe₂O₄ NPs and maximum (2.86 eV) for ZnFe₂O₄ NPs. These calculated values are much higher than the band gap values given in the literature for uncoated Mn_1−xZn_xFe₂O₄ NPs