  Magnetic rotational spectroscopy is based on the use of magnetic micron-size
wires for viscosity measurements. Submitted to a rotational magnetic field with
increasing frequency, the wires undergo a hydrodynamic instability between a
synchronous and an asynchronous regime. From a comparison between predictions
and experiments, the static shear viscosity and elastic modulus of wormlike
micellar solutions are here determined. The values agree with the determination
by cone-and-plate rheometry.
