Invited Paper NT-TuA10
Nanostructures and Ordering Phenomena in Magnetic Colloids Probed by Small Angle Neutron Scattering

Tuesday, October 16, 2007, 4:40 pm, Room 618

Small Angle Neutron Scattering (SANS) allows fluctuations of density, composition and magnetization to be analysed simultaneously on a nanometers length scale. This non-destructive technique was used to characterise magnetic colloids which are of growing interest for advanced medical applications. Such "Ferrofluids" consist of nanosized magnetic particles coated by nonmagnetic organic surfactants and dispersed in carrier liquids. Isotope contrast variation combined with the newly developed technique of polarised neutrons ("SANSPOL") allowed size distributions, compositions and magnetic moments of magnetic core-shell particles and magnetic aggregates to be evaluated precisely beside non-magnetic micelles of similar sizes.¹ In concentrated Ferrofluids an unconventional pseudo-crystalline ordering has been monitored by SANS resulting from strong field-induced inter-particle correlations.^2-3 New stroboscopic techniques have been developed which allowed the dynamics of ordering and realxation to be studied in a time range similar to that of X-ray photon-correlation spectroscopy.⁴

¹Wiedenmann, A., Kammel, M., Heinemann, A., Keiderling, U. J. Phys. : Condensed Matter: 18 (2006) S2713-2736
²Wiedenmann, A., Hoell, A., Kammel, M. , Boesecke, P. Phys Rev. E 68 (2003) 031203
³Klokkenburg, M., Erné, B. H., Meeldijk, J.D., Wiedenmann, A., Pethukov, A.V., Philipse, A.P, Physical Revue Letters 97, 185702 (2006)
⁴Wiedenmann, A., Keiderling, U., Habicht, K., Russina, M., Gähler, R., Physical Review Letters 97, 057202 (2006)