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.