Magnetoresistivity studies of intermetallic uranium compounds and their impact on the understanding of exhibited phenomena

In recent years the occurrence of a large reduction of the electrical resistivity upon application of a magnetic field, called as a giant magnetoresistvity (GMR) effect, first of all observed in some magnetic-multilayer systems like Fe/Cr or Co/Cu, has attracted much attentions due to the possible applications. It turned out that GMR is also possible in various uranium-based compounds which crystalize in layer-like or atomic-chain structures. For some of antiferromagnetic uranium compounds it is sometimes easy to drive a given compound through a metamagnetic (MTM) transition towards an induced ferromagnetic alignment. This is connected with a reorientation of the magnetic moment, which is also the origin of GMR effects in multilayers. Thus, the MTM transition usually causes a drastic reduction of the electrical resistivity, which often exceeds even that of multilayer systems. The high resistance state in bulk uranium antiferromagnets is attributed to the reduction of effective carrier concentration or change in the Fermi surface topology by arising the Fermi level gapping. The transverse magnetoresistance may give also the overall information on the Fermi surface of such uranium-based systems (having open or closed orbits) allowing, e.g. to distinguish a compensated from an uncompensated kind of metal. For some uranium materials the temperature dependence of MR gives evidence of an enormous electron scattering due to the presence of a special kind of spin (magnetic) fluctuations being responsible among others for their superconducting properties.