Fabrication and characterization of magnetite-gadolinium borate nanocomposites

Soft ferromagnetic magnetite (Fe₃O₄)-gadolinium borate nanocomposites have been prepared via a facile hydrothermal approach by using Fe₃O₄, borax (BX) or boric acid (BA) and a simple Gd(III) salt. The products obtained by depositing GdBO₃ over Fe₃O₄ nanoparticles were analyzed by powder X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDS), Transmission Electron Microscopy (TEM), Thermogravimetric Analysis (TGA) and magnetization measurements. The XRD patterns of the nanocomposites showed a bi-phase pattern with reflections matching with those of Fe₃O₄ and GdBO₃. The results showed that the experimental parameters e.g. using either BX or BA, uncoated- or polyethylene glycol (PEG) coated-Fe₃O₄ as the precursors, changing reactant concentrations and the pH, all influence the structure of the borate coating, coverage type, size and morphology of the nanocomposites and saturation magnetization values to some extent. The coating was in the form of vaterite-type orthoborate [Gd₃(B₃O₉)] with BA and triclinic-GdBO₃ with BX, both having the Gd/B ratio of 1/1. PEGylated Fe₃O₄ appeared to be a preferable support for coating with the borate layer to obtain smaller size and uniform composite structures. The nanocomposites prepared with BX displayed typical TEM images where a bunch of spherical 20–40 nm size magnetite nanoparticles were surrounded with a gadolinium borate cloud while nearly cubic, pseudo core-shell nanocomposite particles of 100–150 nm size were obtained with BA at pH 9. This low-cost approach offers the advantages of simplicity, efficiency and allows for the preparation of controlled nanocomposite structures by carefully tuning the experimental conditions. - Highlights: • Soft ferromagnetic magnetite-gadolinium borate nanocomposites. • Hydrothermal synthesis with Fe₃O₄ or PEG-Fe₃O₄, Gd(NO₃)₃·6H₂O, boric acid or borax. • Reactant source and applied molar ratios orientate the structure and the morphology. • GdBO₃ coating of vaterite-type with boric acid and triclinic-type with borax. • Aggregated globular particles (20–50 nm) with borax and cubic particles (100–150 nm) with boric acid.