SIZE VERSUS DISORDER EFFECTS IN THE ELECTRONIC PROPERTIES OF NANOSIZED INTERMEDIATE VALENCE METALS

Nanotechnology is deeply attached to the knowledge of basic mechanisms driving the change of materials properties. For the case of magnets, the properties are drastically modified by the size of the particles and several behaviours can be found, which are object of huge attraction [1]. On the one hand, the coupling between the shell and the core of the particles may affect the superparamagnetic limit [2]. If we study the interparticle magnetic coupling, this is frequently governed by dipolar and/or RKKY interactions, which strongly affects a very important technological magnitude as anisotropy [3]. In other cases, it is the intrinsic magnetic clustered nature of the metal the origin of many magnetic properties in the border of non Fermi liquids, displaying step-like hysteresis loops in the miliKelvin range [4]. But those interesting effects are not restricted to artificial structures; for example they are also found in goethite, a very common mineral in the surface of earth, of great importance for archaeology, biosciences or geology, to cite a few areas [5]. Over the last years we have gathered some experience in dealing with these complex magnetic systems and the arising and persistent key question is whether the size or the disorder in the crystallographic structure is the main driving parameter acting in the magnetic properties. This dilemma is clearly a challenge for