An insight into the role of magnetic anisotropies in the behavior of thin films and arrays of nanoparticles

In this thesis work we discussed the properties of magnetic materials derived by the reduction of at least one of the spatial dimensions under the micrometer scale: in particular we analyzed the origin of some magnetic behaviors in magnetic nanostructures like thin films and arrays of nanodots. One of the important properties which is strongly affected by the size reduction and in which is contained most of the physical description of a magnetic system is the anisotropy energy term: a direction-dependent parameter which strongly contributes to the determination of the equilibrium state and magnetic behavior. We described various nanostructured systems concentrating prevalently on thin films and arrays of interacting nanoparticles and for each system the origin and the physical implications of magnetic anisotropy is discussed. In thin magnetic films, two types of magnetic anisotropies are presented: Perpendicular Magnetic Anisotropy which has a crystalline origin and competes with the shape anisotropy of the thin film producing a singular type of magnetic domains called “stripes” and the Rotatable Anisotropy (the easy magnetic direction is not fixed but could be rotated by means of an external magnetic field). We tried to give a better explanation and modeling of the Rotatable Anisotropy, making a parallelism between the static and dynamic experimental evidences. We performed also a description of the interaction of magnetic dots in arrays with different symmetry and with finite dimensions. In particular we discovered a peculiar space-dependent behavior that we called “Global Configurational Anisotropy”, that has a strong importance when the dimension of the array becomes comparable with the dimension of the nanoparticles.