  We present the results of Monte Carlo simulations of a model of a single
maghemite ferrimagnetic nanoparticle including radial surface anisotropy
distinct from that in the core with the aim to clarify what is its role on the
magnetization processes at low temperatures. The low temperature equilibrium
states are analized and compared to those of a ferromagnetic particle with the
same lattice structure. We have found that the formation of hedgehog-like
structures due to increased surface anisotropy is responsible for a change in
the reversal mechanism of the particles.
