LAUSR

Abstract In present study, a series of spinel ferrite nanoparticles (NPs) with general formula Mn1-xCuxNd0.15Fe1.85O4 (x = 0.0, 0.1, 0.3 and 0.5) have been prepared by sol-gel route. The powder X-ray diffraction (XRD) and Raman spectroscopy revealed the formation of single phase of cubic spinel structure in doped samples. However, a formation of NdFeO3 secondary ortho-ferrite phase has been observed for higher content of x = 0.5. The average crystallite size calculated from Scherrer’s formula has been found in the range 6.5–16.5 nm. The lattice constant (a) estimated using XRD data has been found to increase from 8.4265 A to 8.4501 A on incorporation of Cu2+ ions. FTIR spectra of prepared NPs exhibit two prominent absorption peaks near 600 cm−1 and 400 cm−1 associated to 596 cm−1 and 496 cm−1 band. The dc resistivity measurements with a rise in temperature divulge the typical semiconducting behavior of the as-synthesized samples. The activation energies of the samples have been calculated from Arrhenius plot and found to be in between 0.29 eV and 0.59 eV. Furthermore, the frequency dependent dielectric permittivity, loss tangent and ac conductivity revealed the usual dielectric dispersion. The behavior of dielectric properties highlighted the Debye relaxation peak which is interpreted in the view of Koop’s theory in the light of the Maxwell-Wagner model. Real ( Z ’ ) and imaginary ( Z ’ ’ ) part of impedance confirm the relaxation mechanism associated to the grains and grain boundaries effect. Electron paramagnetic resonance (EPR) pattern shows a broad sharp resonance signal with Lange g-factor varies from 2.04 to 2.18, which is due to dominant spin-exchange interaction between Fe3+, Mn2+, and Cu2+ ions. P-E hysteresis loops found the ferroelectric nature of the ferrite samples. Typical soft ferrimagnetic behavior of Nd3+ substituted Mn–Cu ferrites have been observed at room temperature. The low losses, giant dielectric constant and high resistivity of prepared ferrite NPs can offer several applications like power transformers and microwave devices.