Morphology and Orientational Behavior of Silica-Coated Spindle-Type Hematite Particles in a Magnetic Field Probed by Small-Angle X-ray Scattering

Form factor and magnetic properties of silica-coated spindle-type hematite nanoparticles arc determined from SAXS measurements with applied magnetic field and magnetometry measurements. The particle size, polydispersity and porosity are determined using a core shell model for the form factor. The particles are found to align with their long axis perpendicular to the applied held. The orientational order is determined from the SAXS data and compared to the orientational order obtained from magnetometry. The direct access to both, the orientational order of the particles, and the magnetic moments allow one to determine the magnetic properties of the individual spindle-type hematite particles. We study the influence of the silica coating on the magnetic properties and find a fundamentally different behavior of silica-coated particles. The silica coating reduces the effective magnetic moment of the particles. This effect is enhanced with field strength and can be explained by superparamagnetic relaxation in the highly porous particles.