Influence of samarium doping on structural, elastic, magnetic, dielectric, and electrical properties of nanocrystalline cobalt ferrite

Samarium-doped cobalt ferrite nanoparticles CoSm_xFe_2-xO₄ (0 ≤ x ≤ 0.1) were synthesized using citrate gel auto-combustion method, followed by annealing at 500 °C for 4 h in air. The physical properties of the samples were evaluated using x-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, Mössbauer, magnetic, and dielectric measurement techniques. Rietveld analysis of XRD data confirmed the formation of a single-phase cubic spinel structure for all compositions. Experimental results indicated that doping with samarium (Sm) strongly affected the magnetic properties of CoSm_xFe_2-xO₄ nanoparticles. The values of saturation magnetization (M_S) were reduced from 62.99 (x = 0) to 41.17 (x = 0.1) emu/g. Room-temperature Mössbauer spectra show two sextets (tetrahedral and octahedral sites), and the values of the hyperfine magnetic field (H_hf) of both sextets are found to decrease with Sm-doping. The values of the isomer shift show that all Fe-ions are found in the Fe³⁺ state. The interstitial Sm ions positioned within CoFe₂O₄ realized a dielectric constant dispersion that displayed a maximum at low frequency. With an increase in samarium ion concentration, the two dielectric relaxations reached a very wide range of frequencies. This can be attributed to the contribution of conduction in the grains and grain boundaries of ferrite. Samples with samarium contents of 0.01 and 0.03 showed high impedance stability at 50 and 150 °C, respectively, rendering them suitable for use as a high-frequency window below 1 kHz.