Magnetic nanoparticles are being investigated intensively. They show a core/shell structure in which different magnetic orderings are possible.The superantiferromagnetic TbCu2 presents an antiferromagnetic core and a disordered shell. In fact they constitute a two phase material where new theoretical approaches to understand the anisotropy and the magnetisation process can be tested.These nanoparticles can be interacting magnetically varying greatly the macroscopic response. For technological applications, especially biomedical purposes, it is important to control these interactions to tune the agglomeration.