S. Prass

Publications (5)3.98 Total impact

• Article: Energy barrier distributions of maghemite nanoparticles

  E. Romanus, T. Koettig, G. Glöckl, S. Prass, F. Schmidl, J. Heinrich, M. Gopinadhan, D. V. Berkov, C. A. Helm, W. Weitschies, P. Weber, P. Seidel
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  ABSTRACT: A recently introduced method for the characterization of magnetic nanoparticles (MNPs) based on the analysis of the temperature-dependent Néel relaxation signal (TMRX) has been applied to characterize maghemite particles with different particle size distributions. The samples were made using an improved magnetic fractionation method for a ferrofluid with a broad particle size distribution. The temperature range of the measurement set-up has been extended from 315 K down to 4 K to detect even the smallest particles in the fractions. A mean magnetically relevant particle size has been derived from TMRX and low temperature coercivity measurements and has been compared to the physical size determined by atomic force microscopy (AFM) investigations.
  Nanotechnology. 01/2007; 18(11):115709.
• Article: Magnetic characterization of cobalt nanoparticles by temperature-dependent magnetic relaxation measurements

  E. Romanus, N. Matoussevitch, S. Prass, J. Heinrich, R. Müller, D. V. Berkov, H. Bönnemann, P. Weber
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  ABSTRACT: A recently introduced method for the characterization of magnetic nanoparticles based on the analysis of the dependence of the Néel relaxation signal on the sample temperature (temperature-dependent magnetorelaxometry, TMRX) has been applied to characterize air-stable cobalt particles made by decomposition of Co2(CO)8 in the presence of aluminium-organic compounds. The influence of small changes in the preparation process on the magnetic relaxation behaviour has been studied.A mean magnetically relevant particle size has been derived from TMRX, zero-field cooled magnetisation and low-temperature coercivity measurements and has been compared with a mean physical size determined by transmission electron microscopy investigations. Copyright © 2004 John Wiley & Sons, Ltd.
  Applied Organometallic Chemistry. 01/2004; 18(10):548-552.
• Article: Determination of energy barrier distributions of magnetic nanoparticles by temperature dependent magnetorelaxometry.

  E Romanus, D V Berkov, S Prass, C Groß, W Weitschies, P Weber
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  ABSTRACT: We present a new method for the characterization of magnetic nanoparticles based on the analysis of the dependence of the Néel relaxation signal on the sample temperature. In contrast to the established characterization methods, the new method directly delivers the energy barrier distribution of the magnetic system (in the case of ferrofluid particles or their aggregates). A water based ferrofluid consisting of magnetic nanoparticles with an iron oxide core and a shell of carboxydextran has been magnetically fractionated and immobilized and the fractions have been investigated in a temperature range from 77 to 350 K. The influence of the fractionation process on the distribution of the energy barriers of the particle system has been studied qualitatively.
  Nanotechnology 12/2003; 14(12):1251-4. · 3.98 Impact Factor
• Article: Magnetic nanoparticle relaxation measurement as a novel tool for in vivo diagnostics

  E. Romanus, M. Huckel, C. Grosz, S. Prass, W. Weitschies, R. Brauer, P. Weber
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  ABSTRACT: A measurement system for spatially resolved relaxation measurements of magnetic nanoparticles (MNP) was developed and tested in regard to its applicability for in vivo diagnostics. The system is based on SQUID sensors to detect the magnetic relaxation of MNP and has been optimized to operate in a laboratory environment without any magnetic shielding. Due to a dead time between switching off the magnetizing field and starting the measurement only bound MNP with appropriate Neel relaxation times contribute to the measured signal. The detection limit of the system for MNP was found to be 0.3nmol (17ng) Fe. First investigations on the detection of MNP in mice after intravenous injection showed that the determination of their relaxing magnetization might have the potential to be used as a novel tool for medical imaging.
  Journal of Magnetism and Magnetic Materials. 11/2002; 252:387-389(3).
• Article: Design of a fibre reinforced plastic anticryostat for magnetorelaxometric measurements

  T. Koettig, A. Waldauf, M. Thürk, S. Prass, P. Weber, P. Seidel