Copper doped nickel ferrite nanoparticles: Jahn-Teller distortion and its effect on microstructural, magnetic and electronic properties.

• Synthesis of single-phase ferrite nanoparticles. • Doping of Jahn-Teller active Cu2+ ions. • Lowering of crystal symmetry. • Observation of superparamagnetic behavior. • Good dielectric below 100 Hz. Samples with empirical formula Ni 1-x Cu x Fe 2 O 4 (x = 0.00, 0.25, 0.50, and 1.00) were prepared using chemical route. All the samples showed single spinel phase without any impurity. Average crystallite sizes were observed in the range of 12 nm to 39 nm as calculated by using Williamson-Hall (W-H) graphs. Raman spectra of all samples confirmed the lowering of crystal symmetry of octahedral sublattices with increasing Cu content. Signature of Jahn-Teller distortion due to substitution of Cu2+ (3d9) ions was detected using Raman spectroscopy. Absorption spectra of all the samples were recorded using UV–Vis spectroscopy, which confirmed the opaque character near red and infrared (IR) region. Onset of superparamagnetic behaviour has been observed by incorporating Cu2+ in the nickel ferrite with the mean blocking temperatures for all samples well below 300 K. Dielectric studies revealed that the grain boundaries played a major role in controlling the properties with increase in Cu2+ percentage. [ABSTRACT FROM AUTHOR]