Doped CoFe2O4 Research Articles

Study of transport properties and conduction mechanism of pure and composite resorcinol formaldehyde aerogel doped with Co-ferrite

Abstract A series of resorcinol formaldehyde aerogels (RF aerogels) composite with nanoparticles of CoFe2O4 have been prepared by sol–gel method. Four samples of pure RF aerogels were prepared at different concentrations of Na2CO3 as catalyst (0.02, 0.025, 0.03, and 0.04 wt.%) and four samples of composite RF aerogels were prepared at different concentration of doped CoFe2O4 (0.075, 0.1, 0.125, and 0.15 wt.%; Na2CO3 concentration = 0.03 wt.%). DC electrical conductivity as a function of temperature was studied in the temperature range 25 °C–200 °C for all samples. AC electrical conductivity and dielectric properties were determined using RLC Bridge in the frequency range 100 Hz–1 MHz at different temperature (25–200 °C). The pore size of the samples was determined using positron annihilation lifetime spectroscopy (PALS). RF aerogels are found to exhibit a semiconducting behavior and characterized by two transition temperatures T1 and T2. Also σDC increases with increase of Co-ferrite contents. Pure RF aerogels posses a very low dielectric constant, where the lowest value of ɛ′ is ∼4 times as that of air. ɛ′ decreases with increase of frequency, and increases with increase of temperature. Large overlapping polaron (OLP) is found to be the preferred conduction mechanism in these materials. The results of PALS show that there are two types of pore size in these samples; the first ranges from 1.9 to 2.5 nm, while the second ranges from 3.2 to 5.3 nm.

Structural and Magnetic Properties of Zn Doped CoFe2O4

Zinc doped cobalt ferrite powders were prepared by the solid state reaction method. The effect of zinc substitution on structure, morphology and magnetic properties was investigated. The X-ray analysis confirmed existence of the single phase cubic spinel structure, while Rietveld refinement data showed increasing of lattice parameters with zinc content. In addition, saturated magnetization increased with increasing zinc concentration and it was contained at maximum in CoFe1.9Zn0.1O4 powders. However, the value of coercivity was decreased with zinc doped content. Furthermore, the oxidative states were characterized by X-ray absorption spectroscopy. The results confirm that the structure contained Co2+, Fe3+ and Zn2+ ions.

Synthesis and magnetic properties of octahedral ferrite NiχCo1−χ Fe2O4 nanocrystals

Abstract A series of Ni doped cobalt ferrite compounds with the formula Niχ Co1−χ Fe2O4 where x=0, 0.2, 0.4, 0.6, 0.8, and 1.0 were prepared using a hydrothermal method and subsequently sintered/annealed at 600 °C for 3 h. The influence of the Ni content on the lattice parameter, a, stretching vibration and the magnetization of specimens were subsequently studied. XRD and FTIR were used to investigate structure and composition variations. All samples were found to have a cubic spinel structure. SEM was used to study morphological variations. The results indicate that the average particle sizes are between 30–35 nm with a narrow size distribution along with nanocrystals forming of regular octahedrons. A decrease in the peak to peak line width and increase in resonance field with increasing Ni content were observed from ESR measurements. Based on ESR results, a core-shell type of formation was proposed where the core is made up of undoped CoFe2O4 and the shell is Ni2+ doped CoFe2O4.