  We propose a simple micro-rheology technique to evaluate the viscoelastic
properties of complex fluids. The method is based on the use of magnetic wires
of a few microns in length submitted to a rotational magnetic field. In this
work, the method is implemented on a surfactant wormlike micellar solution that
behaves as an ideal Maxwell fluid. With increasing frequency, the wires undergo
a transition between a steady and a hindered rotation regime. The study shows
that the average rotational velocity and the amplitudes of the oscillations
obey scaling laws with well-defined exponents. From a comparison between model
predictions and experiments, the rheological parameters of the fluid are
determined.
