  Using a novel protocol for mixing oppositely charged colloids and
macromolecules, magnetic clusters and rods are fabricated using 10 nm-iron
oxide nanoparticles and polymers. Here, we show that as the dispersions undergo
the so-called desalting transition, spherical clusters in the range 100 nm - 1
{\mu}m form spontaneously upon dialysis or dilution. With a magnetic field
applied during the dialysis, a one-dimensional growth of the aggregates is
initiated, resulting in the formation of 1 - 100 {\mu}m rods of average
diameter 200 nm. In this paper, we demonstrate that the nanostructured rods
have inherited the properties of the iron oxide particles, namely to be
superparamagnetic. We also discuss the dependence of the magnetic properties as
a function of the nanoparticle diameter.
