Hybridization and pressure effects in UTX compounds

Abstract

The UTX intermetallic compounds (T=transition metal and X=p-electron element) were found to crystallize mainly in two large groups, the orthorhombic TiNiSi and the hexagonal ZrNiAl structure. For both groups, magnetic-ordering phenomena depend sensitively on the 5f-ligand hybridization. The 5f-ligand hybridization is very sensitive to the interatomic distances, which can be effectively controlled by external pressure. Here, we have summarized existing and new pressure studies on various single-crystalline UTX compounds (T=Co, Ni, Ir;X=Al, Ga, Ge). We performed magnetoresistance studies in magnetic fields up to 18 T under external hydrostatic pressure up to 10 kbar. The observed dependencies of the ordering temperatures and the critical fields are compared with the different contributions of the 5f-ligand hybridization, which were deduced from tight-binding calculations. We find relatively weak pressure dependence in compounds, where 5f electrons are more localized, while substantially large pressure effects are found in the more itinerant systems.