Ferro to superparamagnetic transition: Outcome of Ni doping in polyethylene glycol capped CoFe2O4 nanoparticles

Nanocrystalline CoFe2O4 and Ni doped CoFe2O4 were synthesized via chemical precipitation method and their crystal structure, energy gap and magnetic properties were investigated at room temperature. The results revealed that the Ni doping dropped the crystallite size from 23.4 to 6.9 nm. FTIR spectra confirmed the formation of ferrites through the vibrational bonds at 462 and 591 cm−1. UV–Visible diffuse reflectance spectra confirmed that the synthesized ferrite samples are wide bandgap material whose bandgap varies between 3.73 and 4.01 eV. Photoluminescence study confirmed the visible emission of the samples. Transmission electron microscopy analysis confirmed the formation of single domain size of ∼15–72 nm and the morphological tailoring from nanocubes to nanoparticles. Compositional analysis established the consistent mixing of Co, Ni, Fe, and O atoms. The hysteresis analysis confirmed that Ni dopant favours for the magnetic transition from ferro to superparamagnetism. It also infers that Ni dopant reduces the saturation magnetization of cobalt ferrite from 57.83 to 27.13 emu/g and decreased the coercivity from 0.1253 to 0.0139 T as x varies from 0 to 1. Electron paramagnetic resonance spectra confirm the increase in super exchange interaction with the increase in Ni concentration. The dielectric study inferred that the dielectric constant decreases with the increase in frequency. •Ni-doped CoFe2O4 ferrite nanoparticles can be used in red-emission optoelectronic devices.•Ferromagnetic Ni reduces the particle size of CoFe2O4.•Single-domain size of CoFe2O4 is to be 15–72 nm.•Ferrites with wide energygap can be synthesized.