Hybridization effects in selected actinides and their compounds

Many actinide systems exhibit 'unusual' phenomena that differ from the normal text-book behavior. This occurs because the 5f electrons of the actinides and their compounds experience a delicate balance between local-moment and itinerant magnetism. It is well established that strong-electron correlations affect the different properties in such systems. Even though the actinides and their compounds have been extensively studied in recent decades, both experimentally and theoretically, to date, no complete understanding of the full range of their properties has been achieved.; My thesis focuses mainly on understanding the role of 5f electrons and their interactions with the electron states of the surrounding ligands. Particularly, the effect of the 5f-ligand hybridization in the development of bulk properties is investigated.; The experimental studies utilized macroscopic techniques, such as magnetization, electrical-resistivity, specific-heat and resonant-ultrasound-spectroscopy measurements, as well as microscopic techniques, such as neutron-diffraction and muon-spin-resonance studies. The results are used to disentangle the importance of direct 5f--5f overlap and 5 f-ligand hybridization. The following features have been investigated in this thesis: (a) the dual nature of hybridization effects (magnetic moment reduction vs. exchange mediation) was studied for two isostructural uranium compounds U2Pd2Sn and U2Ni2 In; (b) the formation of complex magnetic structures and its connection to the hybridization effects was studied for UCuSn, UPdSn and UPdGe; (c) the tuning of the hybridization to critical values through substitutions was attempted for two single crystals of UCoAl1-xSn x and UNi1-xRh xAl alloys; (d) the effects of compositional deficiencies was studied for the copper-deficient compound in UCu1.5Sn 2; and finally, (e) the influence of strong electron correlations on the elastic properties was studied in the case of alpha-Pu.