Study on the effect of some surface phenomena on the properties of citrate capped cobalt doped ferrites

Abstract Magnetic nanoparticles for applications in life sciences require their uniform dispersion in water which involves surface modification with organic hydrophylic molecules. This study was focused on cobalt doped ferrite nanoparticles known mainly for their usefulness in experimental oncologic thermotherapy. The influence of cobalt doping level was analyzed with focus on crystallinity, granularity and saturation magnetization, based mainly on experimental data provided by X-ray diffractometry, Transmission Electron Microscopy, Vibrating Sample Magnetometry, as well as on the mathematical modeling of data resulted from Small Angle X-ray Scattering measurements. The features of spinel crystallization system of citrate capped cobalt ferrite powders were described with X-ray diffractometry while magnetic core morphology and size polydispersity were evidenced by Transmission Electron Microscopy. Small Angle X-ray Scattering, carried out on fluid samples, revealed theoretically different particle associations for iron oxide and cobalt doped nanoparticles that could be discussed assuming different citrate binding in case of irregular surface. Magnetic properties were studied with Vibrating Sample Magnetometry, revealing superparamagnetism in all samples and also coercivity for cobalt doped ferrites; discussion was developed on the influence of surface crystal defects on saturation magnetization. Citrate ion interaction with magnetic core surface was confirmed by FTIR recordings. The interpretation of cobalt influence on the microstructural and magnetic properties of the nanoparticle series of CoxFe3-xO4 (x = 0; 0.25; 0.50; 0.75; 1) was based on different binding of citrate at the surface metal ions for magnetite and cobalt ferrites.