Superparamagnetic behavior of MnxNi1−xFe2O4 spinel nanoferrites

The glycol-thermal technique was used for the synthesis of MnxNi1−xFe2O4 (x=0.1, 0.3 and 0.5) nanoparticle ferrites from high-purity metal chlorides. Structural parameters, morphology and magnetic properties were investigated using X-ray powder diffraction (XRD), high-resolution transmission electron microscopy, high-resolution scanning electron microscopy, energy-dispersive X-ray spectroscopy, 57Fe Mössbauer spectroscopy, vibrating sample magnetometer (VSM) and VSM on a cryogen free measurement system. The XRD results confirm single-phase formation of the as-prepared samples with average crystallite sizes of about 8.5 nm having the Fd3m space group. The microstrains for the as-prepared samples were relieved by increasing the Mn-concentration, x, while the crystallite sizes and lattice parameters increased slightly. The magnetizations for the sample at x=0.5 were also measured in external applied fields of up to 5 T and at isothermal temperatures from 2 K to 300 K. Small values of coercive fields (≤10Oe), remanent magnetizations and broadening of the Mössbauer spectra at room temperature indicate superparamagnetic like-behavior of the nanoparticle compounds.