Sm3+ induced structural phase transition, spectral, morphological, magnetic, dielectric and impedance properties of Ni0.1Cu0.9SmxFe2–xO4 nanoferrites

Abstract

In the present study, rare earth samarium (Sm3+) substituted Ni–Cu spinel ferrites with the composition of Ni0.1Cu0.9SmxFe2–xO4 (0 ≤ x ≤ 0.05 in steps of 0.01) were synthesized by using the citrate induced sol–gel auto combustion technique. These ferrites' structural, optical, magnetic, and dielectric studies were carried out using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), ultraviolet–visible (UV–vis), a vibrational sample magnetometer (VSM), and an LCR meter. The pure Ni–Cu ferrite exhibits a tetragonal structure owing to the presence of the John Tellar ion (Cu2+). XRD patterns confirm that the tetragonal structure gradually transforms into the cubic spinel structure with samarium substitution. The nano-scale structures of these ferrites were confirmed by the average crystallite size (10.11–20.99 nm) derived from the X-ray diffraction patterns, and grain size (42.60–83.36 nm) assessed from FESEM photographs. The existence of elements according to their chemical composition was verified by using energy dispersive X-ray (EDX) spectra. The absorption bands (υ1 and υ2) detected in FTIR transmission spectra below the wavenumber of 600 cm−1 reveal the stretching vibrations of M−O bonds in the spinel structure at tetrahedral and octahedral locations. The band gap energy obtained from UV absorption reveals the semiconducting nature of the samples. The high saturation magnetization (Ms) is noticed at 15 K temperature for x = 0.02 composition as 32.98 emu/g, while at 300 K for x = 0.01 composition as 27.61 emu/g. The suggested cation distribution is in good agreement with observed and predicted magnetic moment values at 300 K. The expected behavior of ferrites reveals the observed dielectric constant, loss tangent, and ac-conductivity values in the frequency range of 20 Hz–20 MHz. Cole–Cole plots confirm that the impedance contribution is attributed to grain boundaries.