Tuning of the magnetic response in cobalt ferrite CoxFe3-xO4 by varying the Fe2+ to Co2+ molar ratios: Rietveld refinement and DFT structural analysis

• Published in: Journal of alloys and compounds Vol. 695; pp. 2706 - 2716
• Main Authors: Estrada, Samuel Oropeza, Huerta-Aguilar, Carlos A., Pandiyan, T., Corea, Mónica, Reyes-Domínguez, Iván Alejandro, Tavizon, G.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 25.02.2017
• Subjects: Cobalt ferrites; Density of the states (DOS); DFT; Magnetic properties; Molecular orbitals (MO); Rietveld refinement; Cobalt ferrites; Density of the states (DOS); Rietveld refinement; DFT; Molecular orbitals (MO); Magnetic properties
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2016.11.187

Magnetic cobalt ferrites CoxFe3-xO4 (x = 3, 2.25, 1.5, 0.75, 0.0) were synthesized and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Different molar ratios of Fe2+ to Co2+ ions in the initial salt solutions were used to yield cobalt ferrites, and the results show that the ratio Co2+:Fe2+ (50:50) yields smaller size (<100 nm) of cobalt ferrite than those from other proportional mixtures. The XRD and Rietveld refinement data reveal that a characteristic peak, corresponding to the Fe2O3 (α-hematite) almost disappeared in CoxFe3-xO4 (x = 0.75), suggesting that Co ions are notably favoring the spinel structure formation of the cobalt ferrite; this is consistent with the Density functional theory (DFT) study where a lower total energy was observed for Co3O4 than for Fe3O4, thus the latter favors a substitution reaction to yield a stable cobalt ferrite. Thus a reduction in the bandgap (HOMO-LUMO) as well as a higher density of electronic states is observed for Fe1.5Co1.5O4 in the Molecular Oribital (MO) frontier region. This synergistic effect, i.e., the incorporation of Co ions in Fe sites of Fe3O4, considerably increases magnetization saturation (Ms) to 104 emu/g and reduces coercivity (0.70 kOe), for Co1.5Fe1.5O4, exhibiting a trend towards to a superparamagnetic behavior. The influence of the molar ratios Fe2+/Co2+ and thermal treatments on the magnetization saturation and coercivity are also studied. [Display omitted] •Effect of Co/Fe ratio on the magnetic saturation of cobalt ferrate.•Rietveld refinement and DFT studies on cobalt ferrates with different molar Co/Fe ratio.•Why CoxFe3-xO4 (x = 0.75 or 1.5) exhibits high magnetic saturation.•Correlation of substitution (%) of Fe by Co in Fe3O4 with magnetic saturation.