Novel ordered phases and quantum criticality of 4f-electron systems in high magnetic fields and ultra-low temperatures

In this thesis, we have studied the properties of the two 4f-electron systems PrOs4Sb12 and Cd-doped CeIrIn5 in high magnetic fields and in ultra-low and low temperatures, respectively. Experiments have been carried out at the High Field Magnet Laboratory, Radboud University, Nijmegen, the Netherlands, and the Department of Physics, Royal Holloway, University of London, Egham, United Kingdom. By means of magnetic susceptibility and torque magnetometry experiments, we have studied phase transitions, ordered phases, and quantum criticality, as well as Fermi surface properties through the de Haas – van Alphen effect.