ABSTRACT
This chapter provides theoretical interest on dipolar effects and more especially on dense nanoparticles even if the formalism of energy minimization is suited for all samples. It discusses short historical view of experimental techniques and numerical simulations which are available for detecting magnetic structures in nanoparticles. The chapter introduces spin, angular momentum, and magnetic interactions, and considers the structure of magnetic materials and basic magnetic states. It deals with dynamic effects such as magnetic excitations and critical effects in nanoparticles. The chapter explains some of the numerous parallel topics where nanoparticles are submitted to similar long-ranged interactions, from nuclear spins up to liquid crystals and multiferroic materials as well as neural networks with long-ranged synaptic couplings. The variational treatment of energy minimization when dealing with two-dimensional and three-dimensional magnetic nanoparticles in presence of dipolar interactions follows with a special interest devoted to basic units, that is, small enough samples.
