  Spin-coating technique is very fast, cheap, reproducible, simple and needs
less material to fabricate films of particulate systems/colloids. Their
thickness and uniformity may be controlled by means of external fields. We
apply magnetic fields during the spin-coating of a moderately concentrated
superparamagnetic colloid (made of silica coated magnetite particles). We study
the influence of different magnetic field configurations (homogeneous and
inhomogeneous) on the resulting spin-coated deposits and compare experimental
results under various conditions. Superparamagnetic colloids behave as,
non-Newtonian, magnetorheological fluids. Their viscosity vary significantly
under applied magnetic fields. We measure and compare the effect of uniform and
non-uniform magnetic fields on their relative effective viscosity, using the
spin-coated deposits and a previously existing model for simple colloids. The
mechanisms involved in the deposits formation under different experimental
conditions are also discussed. In particular, we show that the magnetophoretic
effect plays an important role in the spin-coating of magnetic colloids
subjected to non-uniform magnetic fields. We characterize an effective
magnetoviscosity in non-uniform magnetic fields that is largely influenced by
the magnetophoretic effect that enhances the flow of the magnetic fluid.
