Optimization of magnetism and visible photoluminescence emission of Ni-Co nanoferrite

Zn_xCo_1-xFe₂O₄(0 ≤ x ≤ 1.0) nanoferrites were synthesized using the glycol-thermal technique. Various analytical characterizations were employed to acquire the structural information of the resultant nanoferrites. The XRD analysis and Rietveld refinement verified the presence of a cubic spinel structure, with crystallite sizes ranging from 7 to 19 nm, correlating well with TEM and SEM results which also revealed spherical shaped and agglomerated nanoparticles. The magnetization measurements revealed a strong effect of Zn²⁺ substitution. The saturation magnetization (M_s) changes significantly with Zn concentration, peaking at 58 emu/g in pure CoFe₂O₄ (x = 0). Upon including Zn²⁺ ions, magnetization increased to 63 emu/g, which then reduced with further increase in Zn content. The variation was associated with cation distribution and replacement of magnetic Co with nonmagnetic Zn ions. H_C values also decrease from 470 to 17Oe. ESR tests revealed g-values ranging from 1.251 to 2.962, showing a significant exchange contact between nanoparticles based on their shape and crystalline structure. Zn_xCo_1-xFe₂O₄ nanoferrites are suited for low-frequency devices owed to their low g values. The deterioration of the state to quadrupole doublet in Mössbauer spectroscopic data revealed the transition from ferromagnetic to paramagnetic states. At blocking temperatures of 25 K, 70 K, and 280 K, FC and ZFC revealed Zn_xCo_1-xFe₂O₄ nanoferrites for CoFe₂O₄ (x = 0), Zn_0.5Co_0.5Fe₂O₄ (x = 0.5), and ZnFe₂O₄ (x = 1.0), respectively. Photoluminescence (PL) measurements revealed the blue-violet fluorescence caused by the defects. Small values of M_S and H_C, together with paramagnetic properties observed in Mössbauer spectroscopy results makes the synthsized Zn-Co ferrites are suitable for applications in electronic swtiching devices and during the magnetic hyperthema treatment.