THEORETICAL STUDIES OF MAGNETIC MATERIALS AT THE MICROMETER AND NANOMETER SCALE

Abstract

In this thesis we analyzed, from a theoretical point of view, different aspects of the magnetic system at the micrometer and nanometer scale. We calculated the magnetostatic interaction energy in an array of magnetic nanowires considering the magnetic structure of each nanowire as a single ferromagnetic domain; we show that the dipole–dipole interaction among the wires overestimates the true interaction energy by several orders of magnitude at closer interwire distances. Also, we analyze the dynamics of two interacting nanoparticles in the presence of an applied magnetic field including the dipolar and exchange interactions at a fixed temperature. We found that the magnitude of the total system magnetization is not constant; but it is a fluctuating time dependent function. Finally, we studied the equilibrium statistical mechanics for noninteracting anisotropic nanoparticles. The thermodynamics quantities are derived using our analytical expression for the partition function and we found that, a maximum of the magnetization curve as function temperature is attained when the anisotropy field is perpendicular to the external magnetic field.