Paradoxical Magnetic Cooling in a Structural Transition Model

Peter Borrmann   Phone: +49-(0)441-798-3362   Fax: +49-(0)441-798-3201
Heinrich Stamerjohanns   Phone: +49-(0)441-798-3467   Fax: +49-(0)441-798-3201
E.R. Hilf   Phone: +49-(0)441-798-2543   Fax: +49-(0)441-798-3201
David Tománek

Small systems group   University of Oldenburg, Germany


Date: 20000904

Article: published in European Physical Journal B 19, 117-119 (2001)

Paradoxical magnetic cooling, ferrofluids.

In contrast to the experimentally widely used isentropic
demagnetization process for cooling to ultra-low temperatures we
examine a particular classical model system that does not cool, but
rather heats up with isentropic demagnetization. This system consists
of several magnetite particles in a colloidal suspension, and shows
the uncommon behavior of disordering structurally while ordering
magnetically in an increasing magnetic field. For a six-particle
system, we report an uncommon structural transition from a ring to a
chain as a function of magnetic field and temperature.

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Heinrich Stamerjohanns on September 4th, 2000