  The effect of periodic magnetic perturbations on the rheological properties
of a low concentration magnetorheological dispersion is studied experimentally.
It is found that an important increment in the measured viscosity occurs when
in addition to a static field a magnetic periodic perturbation is applied. The
magnitude of these changes depend on the amplitude and frequency of the
perturbation as well as on the simultaneity of the application of the static
field and the perturbation. These findings are discussed in terms of the
observed rearrangement of the cluster structure in the dispersion.
