Sample holder for SAXS measurements under static magnetic field: induced anisotropy in ferrofluid

D. F. CORAL; P. MENDOZA ZÉLIS; J. M. POLLI; M. E. DE SOUSA; M. B. FERNÁNDEZ VAN RAAP

Activity Report 2012: LNLS

Ministry of Science and Technology / Brazilian Association for Synchrotron Light Technology

Año: 2013;

The mica cell sample holder available at SAXS2 beam line of Brazilian Synchrotron Light Laboratory was modified to record SAXS data under homogenous magnetic fields applied perpendicular to x-ray beam. Various field strengths (H) were achieved by a consecutive pile up of ring shaped permanent-magnets. The field homogeneity in sample location was established by simulations. This sample holder is suitable for liquid, gel phases or liquid crystals samples. An aqueous colloid composed of Fe3 O4 magnetic nanoparticles coated with citric acid (NPs) was measured under various static magnetic fields to experimentally test the design. The magnetic particles are single magnetic domain with meansize d = 5.16±1.67 nm and are electrostatically stabilized in the liquid carrier by charged end molecules (COOH-). Anisotropic structuring driven by the field is due to interparticle dipolar and Zeeman interactions. A parameter to characterize the anisotropy degree (A(q, H)) is defined as the difference between scattering intensities recorded at the detector area in a direction perpendicular (I⊥ ) and parallel (I ) to applied field direction. Anisotropy increases with increasing field strength.