Calculated magnetic properties of two-dimensional arrays of nanoparticles at vanishing temperature

We calculate the magnetic properties of a monolayer of spherical and uniaxial single domain magnetic nanoparticles, with dipolar interaction, at vanishing temperature. The particles are located on the sites of a lattice of either square or hexagonal structure. We focus on both the magnetic properties (magnetization curve, coercive field) and the orientational structure of the magnetic moments in the layer. We find that the structure of the lattice plays an important role on the orientational structure of the moments, especially in the case of a strong dipolar coupling: an ordered state takes place at a length scale of a few interparticle distances, the nature of which (ferromagnetic or antiferromagnetic) changes with the symmetry of the lattice. However, the magnetic properties are nearly independent of the structure of the lattice. (C) 2001 American Institute of Physics.