title: Simultaneous Study of Brownian and Néel Relaxation Phenomena in Ferrofluids by Mössbauer Spectroscopy.
abstract: We demonstrate the ability of Mössbauer spectroscopy to simultaneously investigate Brownian motion and Néel relaxation in ferrofluidic samples. For this purpose, Mössbauer spectra of coated iron oxide nanoparticles with core diameters of 6.0-26.4 nm dissolved in 70 vol % glycerol solution were recorded in the temperature range of 234-287 K and compared to low-temperature spectra without Brownian motion. By comparison to theory, we were able to determine the particle coating thickness and the dynamic viscosity of the fluid from the broadening of the absorption lines (Brownian motion), as well as the state of Néel relaxation. Results from Mössbauer spectroscopy were crosschecked by AC-susceptometry at several temperatures for Brownian motion and in the high-frequency regime (100 Hz-1 MHz) for Néel relaxation.
authors.affiliation: Faculty of Physics and Center for Nanointegration Duisburg-Essen (CENIDE), University of Duisburg-Essen , Lotharstr. 1, 47048 Duisburg, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Landers
authors.affiliation: Faculty of Physics and Center for Nanointegration Duisburg-Essen (CENIDE), University of Duisburg-Essen , Lotharstr. 1, 47048 Duisburg, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Salamon
authors.affiliation: Institute of Electrical Measurement and Fundamental Electrical Engineering, TU Braunschweig , Hans-Sommer-Str. 66, 38106 Braunschweig, Germany.
authors.forename: H
authors.initials: H
authors.lastname: Remmer
authors.affiliation: Institute of Electrical Measurement and Fundamental Electrical Engineering, TU Braunschweig , Hans-Sommer-Str. 66, 38106 Braunschweig, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Ludwig
authors.affiliation: Faculty of Physics and Center for Nanointegration Duisburg-Essen (CENIDE), University of Duisburg-Essen , Lotharstr. 1, 47048 Duisburg, Germany.
authors.forename: H
authors.initials: H
authors.lastname: Wende
keywords: AC-susceptometry; Brownian motion; Ferrofluids; Mössbauer spectroscopy; magnetic nanoparticles; superparamagnetism