Size dependent structural and magnetic properties of Co(1-x) Nix Cr2O4 nanoparticles (x = 0.15, 0.20)

This study examines the structural and magnetic characteristics of Co(1-x)NixCr2O4 (x = 0.15, 0.20) compounds synthesised using the co-precipitation technique and calcined at 500 degrees C and 900 degrees C respectively. X-ray diffraction studies reveal the structure of the synthesized samples is face-centered cubic with space group Fd-3m. The particle sizes and morphology were examined by using transmission electron microscopy, and the size ranges from 64 +/- 10 nm to 105 +/- 15 nm for the 900 degrees C and 7 +/- 2 and 8 +/- 2 nm for the 500 degrees C calcined samples. Field-cooling and zero-field-cooling magnetization measurement protocols were used to investigate the materials' magnetic characteristics. The Curie temperature (T-C) decreases from 91 +/- 0.5 K to 85 +/- 0.3 K as the Ni concentration increases from x = 0.15-0.20. Additionally, an increase in the T-C value is seen for both compositions when the particle size is decreased. Spiral ordering is observed at a transition temperature TS for the samples calcined at 900 degrees C, while no evidence for TS was seen for samples calcined at 500 degrees C. Magnetization measurements as a function of field, M(mu H-0), at several constant temperatures, show that the coercivity reduces with an increase in temperature in all samples. The Co(1-x)NixCr2O4 (x = 0.15, 0.20) samples calcined at 900 degrees C exhibit superparamagnetic behaviour with a small ferrimagnetic hysteresis loop. Furthermore, this paper evaluates the contribution of ferrimagnetic, superparamagnetic, and paramagnetic phases to the total M(mu H-0) curve for Co(1-x)NixCr2O4 (x = 0.15, 0.20) calcined at 900 degrees C through simulation. In addition, a modified Langevin simulation, incorporating a particle size distribution term, is performed for the Co(1-x)NixCr2O4 (x = 0.15, 0.20) samples calcined at 500 degrees C. From the simulations, it is clear that all samples show evidence of significant superparamagnetic contributions to the total saturation magnetization because of the small particles present.