Agglomeration and chain formation in ferrofluids: Two-dimensional x-ray scattering

Tobias Kruse, Hans-Georg Krauthäuser, Anna Spanoudaki, and Rolf Pelster
Phys. Rev. B 67, 094206 – Published 21 March 2003
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Abstract

We present a comprehensive study of field-induced anisotropy in ferrofluids using two-dimensional small-angle x-ray scattering. On application of a homogeneous magnetic field, magnetite particles form anisotropic clusters with preferred orientation parallel to the field. The orientation of single nonspherical particles contributes little to structural anisotropy, since their effective axis ratio is only about 1.05. We determine the average radius of particles in clusters to be of the order of the mean particle radius in the ferrofluid, i.e., 4–5 nm. Therefore, particles of all sizes contribute to cluster formation. Since the thermal energy exceeds the magnetic dipole-dipole interaction of small particles, thermally stable clusters cannot form without an additional interaction energy. We show that van der Waals interaction yields a significant contribution that cannot be neglected in polydisperse systems.

  • Received 29 July 2002

DOI:https://doi.org/10.1103/PhysRevB.67.094206

©2003 American Physical Society

Authors & Affiliations

Tobias Kruse, Hans-Georg Krauthäuser*, Anna Spanoudaki, and Rolf Pelster

  • II. Physikalisches Institut der Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany

  • *Present address: Institut für Grundlagen der Elektrotechnik und elektromagnetische Verträglichkeit, Otto-von-Guericke-Universität Magdeburg, Postfach 4120, 39016 Magdeburg, Germany.
  • Present address: Laboratoire de Physique, Ecole Normale Supérieure de Lyon, 46, Allée d’Italie, Lyon Cedex 07, France.

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Issue

Vol. 67, Iss. 9 — 1 March 2003

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