NANOSCALE MAGNETIC PARTICLES - SYNTHESIS, STRUCTURE AND DYNAMICS

In recent years, new synthetic routes, which include wet techniques an d synthesis in confined geometries, have been developed for the prepar ation of nanoscale magnetic particles. The shape of the particles obta ined is usually smooth and rounded all over, due to the influence of t he surface energy. The final shape, however, depends on the preparatio n method and is much influenced by the substrate used, as this may str ess and deform the particles in order that they adapt to it. Changes i n lattice parameters, in comparison to the bulk, and surface modificat ions give way in many cases to changes in the magnetic and transport p roperties. For very small ferromagnetic metal particles (clusters), bo th enhanced magnetism, due to localization of the valence d-electrons, and giant magnetic moments for some nonmagnetic clusters are observed . Magnetic phenomena in real single-domain particles reveal that the s tatistics of the magnetization reversal cannot be described by a therm al activation over a single-energy barrier. Macroscopic quantum tunnel ling of magnetization is observed at very low temperatures in several systems, Other interesting electrical and magnetic phenomena, such as finite size effects, coercivity enhancement due to surface effects, an d giant magnetoresistance, are observed in fine particle systems.