Ferrogels, i.e. swollen polymer networks into which magnetic particles are
immersed, can be considered as "smart materials" since their shape and
elasticity can be controlled by an external magnetic field. Using molecular
dynamics simulations on the coarse-grained level we study a ferrogel in which
the magnetic particles act as the cross-linkers of the polymer network. In a
homogeneous external magnetic field the direct coupling between the orientation
of the magnetic moments and the polymers by means of covalent bonds gives rise
to a deformation of the gel, independent of the interparticle dipole-dipole
interaction. In this paper we report quantitative measurements of this
deformation, the gel's elastic moduli and its magnetic response. Our results
demonstrate that these properties depend significantly on the topology of the
polymer network
