In this work Mn_xCo_1−xFe₂O₄ nanoparticles (NPs) were synthesized using a chemical co-precipitation method. Phase purity and structural analyses of synthesized NPs were performed by X-ray diffractometer (XRD). Transmission electron microscopy (TEM) reveals the presence of highly crystalline and narrowly-dispersed NPs with average diameter of 14 nm. The Fourier transform infrared (FTIR) spectrum was measured in the range of 400–4000 cm⁻¹ which confirmed the formation of vibrational frequency bands associated with the entire spinel structure. Temperature-dependent magnetic properties in anti-ferromagnet (AFM) and ferromagnet (FM) structure were investigated with the aid of a physical property measurement system (PPMS). It was observed that magnetic interactions between the AFM (Mn) and FM (CoFe₂O₄) material arise below the Neel temperature of the dopant. Furthermore, hysteresis response was clearly pronounced for the enhancement in magnetic parameters by varying temperature towards absolute zero. It is shown that magnetic properties have been tuned as a function of temperature and an externally-applied field.

Bimagnetic monodisperse CoFe₂O₄/Fe₃O₄ core/shell nanoparticles have been prepared by solution evaporation route. To demonstrate preferential coating of iron oxide onto the surface of ferrite nanoparticles X-ray diffraction (XRD), High resolution transmission electron microscope (HR-TEM) and Raman spectroscopy have been performed. XRD analysis using Rietveld refinement technique confirms single phase nanoparticles with average seed size of about 18 nm and thickness of shell is 3 nm, which corroborates with transmission electron microscopy (TEM) analysis. Low temperature magnetic hysteresis loops showed interesting behavior. We have observed large coercivity 15.8 kOe at T = 5 K, whereas maximum saturation magnetization (125 emu/g) is attained at T = 100 K for CoFe₂O₄/Fe₃O₄ core/shell nanoparticles. Saturation magnetization decreases due to structural distortions at the surface of shell below 100 K. Zero field cooled (ZFC) and Field cooled (FC) plots show that synthesized nanoparticles are ferromagnetic till room temperature and it has been noticed that core/shell sample possess high blocking temperature than Cobalt Ferrite. Results indicate that presence of iron oxide shell significantly increases magnetic parameters as compared to the simple cobalt ferrite.

Ni substituted Mn-Co ferrite nanoparticles (NixCo0.8-xMn0.2Fe2O4), with doping content (x) varying from 0 to 0.1, have been synthesized via co-precipitation route. X-ray diffraction reveals the formation of single phase spinel ferrite structure. Fourier transform infrared spectroscopy exhibits presence of two absorption bands appearing at 500-600 cm-1 which are characteristic feature of spinel ferrites. Microstructural analyses were carried out by using scanning electron microscope, transmission electron microscope and energy dispersive X-ray spectroscope which determine the particle size and chemical composition of the synthesized nanoparticles. From TEM results, average particle size was determined to be about 20 nm, which is in good agreement with XRD results. Magnetic results show increase in coercivity and decrease in saturation magnetization with increasing doping concentration.