Characterization and Magnetic Behaviour of Nanosized Binary Spinel Ferrites Synthesized by Low Temperature Hydrothermal Method and their Stability in Aqueous Suspensions

Abstract

INTRODUCTIONFerro spinel compounds possess high permeability so that they can be used in electronics [1][2][3], in microwave and high density information storage devices [4], as ferrofluids [5] and magnetic drug delivery materials [6], etc. Spinel ferrites, possessing cubically close packed array of oxygen anions with the metallic ions occupy two crystallographically different sites, i.e. octahedral [B] and tetrahedral (A) site. Three kind of magnetic interactions are possible, between metallic ions, through the intermediate O ions, by super-exchange mechanism, namely, A-A interaction, B-B interaction and A-B interaction. It has been established experimentally that these interaction energies are negative and hence induce an anti-parallel orientation.Due to the specific electronic configurations of cations and the types of super-exchange interactions among them, the magnetic properties of ferrites are strongly dependent on the occupancy and exchange of cations in the two sites. In spinel ferrites, direct interactions are negligible, due to the large distance between cations. Super-exchange interaction occurs between two metal cations through the existence of a bridging oxygen ion. It involves the temporary transfer of one oxygen 2p electron to a neighboring metal ion. The A-B interaction is the strongest super-exchange interaction in the spinel structure, followed Cobalt ferrite, nickel ferrite and zinc ferrite spinel oxides are synthesized by low temperature hydrothermal method using ethylenediamine tetracetic acid (EDTA) as complexing agent. FTIR and XRD studies show the formation of pure and single spinel phase. The average crystalline size was determined from X-ray diffraction line broadening using Scherrer equation. FE-SEM studies revealed that all the synthesized ferrites are having nearly octahedron crystals with an average particle size of 20 to 40 nm. Magnetic behavior of cobalt ferrite, nickel ferrite and zinc ferrite spinels studied by vibrating sample magnetometer at room temperature shows ferromagnetic behaviour of cobalt ferrite, super paramagnetic nature of nickel ferrite and non-magnetic behaviour of zinc ferrite. Zeta potential measured at various pH conditions shows that cobalt ferrite and nickel ferrite can be used for the preparation of magnetic nanofluids with stable colloidal dispersion at 4.5 > pH < 7.5 and 3.5 > pH < 9.5, respectively.