Structure investigations of barium hexaferrite ferrofluids and their precursors by sans with polarized neutrons

A. Hoell¹ - R. Müller² - A. Heinemann¹ - A. Wiedenmann¹

¹ Hahn-Meitner-Institute, Department of Structural Research, D-14109 Berlin, Germany
² Institut für Physikalische Hochtechnologie e.V. Jena, D-07745 Jena, Germany

Abstract
We report on Small Angle Neutron Scattering investigations using POLarized neutrons (SANSPOL) of ferrofluids based on superparamagnetic barium hexaferrite nano-crystals. The combination of magnetic and isotopic (by H-D exchange) contrast variations of the carrier liquid allows magnetic and non-magnetic components to be quantitatively analyżed. In the ferrofluids surfactants form a shell around the nano-crystals, which was found impenetrable for the carrier liquids. Additionally, magnetic aggregates and free surfactant molecules were detected. The derived magnetic contrast reveals a reduced but homogeneous magnetization of the core. The nano-crystals were grown in solid state during crystallization of glasses. These precursor states were investigated by SANSPOL using the nuclear-magnetic cross-term that excludes all non-magnetic structures in the glass ceramics. The magnetic scattering length density is found constant inside the particles and has the same value as the cores in the ferrofluids. Furthermore, the chemical preparation steps have no influence on the magnetic structure of the nano-crystals. Figs 5, Refs 15.