title: Dynamics of field-induced ordering in magnetic colloids studied by new time-resolved small-angle neutron-scattering techniques.
abstract: The reversal of magnetic moments of nanoparticles in concentrated Co ferrofluids was monitored in an oscillating magnetic field by new time-resolved stroboscopic small-angle neutron-scattering techniques. Time resolution in the micros range was achieved by using a pulsed beam technique, TISANE, while in continuous mode resolution was limited by the wavelength spread to about 1 ms. The frequency dependence of anisotropic scattering patterns has been modeled using Langevin dynamics. The dynamics follows a two step mechanism: field-induced ordering is governed by fast Brownian rotation of nanoparticles with a characteristic time of about 160 micros. Magnetic relaxation of locally ordered domains of about 100 nm in size takes place within a few seconds by Brownian rotation or by Néel type rotation of magnetic moments.
authors.affiliation: Hahn-Meitner-Institut, Structure Research, Glienicker Strasse 100, D-14109 Berlin, Germany. wiedenmann@hmi.de
authors.forename: A
authors.initials: A
authors.lastname: Wiedenmann
authors.forename: U
authors.initials: U
authors.lastname: Keiderling
authors.forename: K
authors.initials: K
authors.lastname: Habicht
authors.forename: M
authors.initials: M
authors.lastname: Russina
authors.forename: R
authors.initials: R
authors.lastname: Gähler