Phase diagrams of REFeAsO(1-x)F(x) materials. Macroscopic and nanoscopic experimental investigation

This Ph.D. dissertation deals with an experimental investigation of the magnetic properties of REFeAsO1-xFx oxy-pnictide materials both in the magnetic and in the superconducting regions of the typical electronic phase diagram. Such electronic ground states are properly tuned by means of chemical substitutions (leading to charge doping) and external pressure. The discussed topics are divided into two main parts, each of them relative to one of the two cited regions. Such distinction is also relative to the general features of the employed experimental techniques. Accordingly, in the first part the superconducting phase is studied from a macroscopic point of view by means of measurements of dc magnetization and ac magnetic susceptibility. On the other hand, local-probe techniques like muon spin spectroscopy and nuclear magnetic resonance are employed in the second part in order to describe the magnetic spin density wave ground state at low values of electron doping.