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

Abstract

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 °C and 900 °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 °C and 7 ± 2 and 8 ± 2 nm for the 500 °C calcined samples. Field-cooling and zero-field-cooling magnetization measurement protocols were used to investigate the materials' magnetic characteristics. The Curie temperature (TC) 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 TC 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 °C, while no evidence for TS was seen for samples calcined at 500 °C. Magnetization measurements as a function of field, Mμ0H, 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 °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 Mμ0H curve for Co(1−x)NixCr2O4 (x = 0.15, 0.20) calcined at 900 °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 °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.