Physical properties of magnetic nanostructures

Abstract

This thesis is about the physical characterization of a diverse set of magnetic nanostructured system from a theoretical point of view. The methods used in this study are density functional theory and Heisenberg Monte-Carlo.The rst Chapter is a longer introduction, which describes the main motivationsand conclusions of each chapter. Chapter Chapter 2 explains the theoretical methods, concepts, and tools used throughout this thesis. The rst systems studied (Chapter 3) are small Co{Cu clusters, with emphasis on thesearch of ground-state structures. The results show the possibility of Co{Cu nanoalloys and two sources of magnetism where found, coming from d and s electron. Next, in Chapter 4, is calculated the deposition of a Mn adatom and ad-dimer on a noble metal surface. In each case the adsorption is energetically favorable, but the Mn2 formation only is stable for an Ag and Cu surfaces.Chapters 5, 6 deal with 1-D nanostructures: nanowires and nanotubes. With emphasis in measuring their magnetic anisotropy energy. It was found that the atomic detail of the inter-structure matching can change the easy axis.Magnetite nanoparticles are modelled in Chapter 7, using a Heisenberg-Monte Carloapproach. Both equilibrium and hysteretic properties are studied. The main conclusion is that the surface anisotropy can act as a driving force for exchange-bias.