  We study self-assembly in a colloidal suspension of magnetic particles by
performing comprehensive molecular dynamics simulations of the Stockmayer (SM)
model which comprises spherical particles decorated by a magnetic moment. The
SM potential incorporates dipole-dipole interactions along with the usual
Lennard-Jones interaction and exhibits a gas-liquid phase coexistence observed
experimentally in magnetic fluids. When this system is quenched from the
high-temperature homogeneous phase to the coexistence region, the
non-equilibrium evolution to the condensed phase proceeds with the development
of spatial as well as magnetic order. We observe density-dependent coarsening
mechanisms - a diffusive growth law $\ell(t)\sim t^{1/3}$ in the nucleation
regime, and hydrodynamics-driven inertial growth law $\ell(t)\sim t^{2/3}$ in
the spinodal regimes. [$\ell(t)$ is the average size of the condensate at time
$t$ after the quench.] While the spatial growth is governed by the expected
conserved order parameter dynamics, the growth of magnetic order in the
spinodal regime exhibits unexpected non-conserved dynamics. The asymptotic
morphologies have density-dependent shapes which typically include the
isotropic sphere and spherical bubble morphologies in the nucleation region,
and the anisotropic cylinder, planar slab, cylindrical bubble morphologies in
the spinodal region. The structures are robust and nonvolatile and exhibit
characteristic magnetic properties. For example, the oppositely magnetized
hemispheres in the spherical morphology impart the characteristics of a {\it
Janus particle} to it. The observed structures have versatile applications in
catalysis, drug delivery systems, memory devices, and magnetic photonic
crystals, to name a few.
