Effect of rare earth elements on low temperature magnetic properties of Ni and Co-ferrite nanoparticles

The Er/Sm-substituted nickel ferrite and Sm-substituted cobalt ferrite nanomaterials were synthesized via citrate-gel autocombustion technique. The diffraction pattern revealed the formation of cubic spinel structure. In addition, the structural parameters such as lattice constant (a), average crystallite size (D) and X-ray density (rho(x)) were also evaluated. The surface morphology was analyzed using field emission scanning electron microscope (FESEM) and transmission electron microscopes (TEM). Besides, the low temperature magnetic properties were studied using magnetization versus temperature (M - T) & magnetic field (M - H) curves. The obtained results attributed that the NiSm0.1Fe1.9O4 (NSF) and NiEr0.1Fe1.9O4 (NEF) samples exhibited the superparamagnetic property pertaining almost zero value of coercivity (H-c) and remanence (M-r) at 5 K & 300 K. Moreover, the superparamagnetic property was evidenced by zero-field cooled (ZFC) and field cooled (FC) curves. Interestingly, the CoSm0.1Fe1.9O4 (CSF) sample performed the soft magnetic behavior with increase of temperature from 5 to 300 K by possessing certain numerical values of H-c and M-r.