Nanostructure and Magnetic Field Ordering in Aqueous Fe3O4 Ferrofluids: A Small-Angle Neutron Scattering Study

Abstract

Despite the importance of reducing production costs, investigating the hierarchical nanostructure and magnetic field ordering of Fe₃O₄ ferrofluids is also important to improve its application performance. Therefore, we proposed an inexpensive synthesis method in producing the Fe₃O₄ ferrofluids and investigated their detailed nanostructure as the effect of liquid carrier composition as well as their magnetic field ordering. In the present work, the Fe₃O₄ ferrofluids were successfully prepared through a coprecipitation route using a central precursor of natural Fe₃O₄ from iron sand. The nanostructural behaviors of the Fe₃O₄ ferrofluids, as the effects of the dilution of the Fe₃O₄ particles with H₂O as a carrier liquid, were examined using a small-angle neutron spectrometer (SANS). The Fe₃O₄ nanopowders were also prepared for comparison. A single lognormal spherical distribution and a mass fractal model were applied to fit the neutron scattering data of the Fe₃O₄ ferrofluids. The increasing carrier liquid composition of the fluids during dilution process was able to reduce the fractal dimension and led to a shorter length of aggregation chains. However, it did not change the size of the primary particles or building block (approximately 3.8 nm) of the Fe₃O₄ particles. The neutron scattering of the Fe₃O₄ ferrofluids under an external magnetic field in the range of 0 to 1 T exhibited in a standard way of anisotropic phenomenon originating from the nanostructural ordering of the Fe₃O₄ particles. On the other hand, the Fe₃O₄ powders did not show anisotropic scattering under an external field in the same range. Furthermore, the magnetization curve of the Fe₃O₄ ferrofluids and nanopowders exhibited a proper superparamagnetic character at room temperature with the respective saturation magnetization of 4.4 emu/g and 34.7 emu/g.