| UBe{dollar}sb{lcub}13{rcub}{dollar} is a metal which belongs to the class of materials called heavy-fermion systems (HFS). At high temperatures UBe{dollar}sb{lcub}13{rcub}{dollar} can be described as a system of localized magnetic moments (U{dollar}sp{lcub}3+{rcub}{dollar} ions) which weakly interact with the conduction electrons. At low temperatures, however, the interaction causes the conduction electrons to develop an exceptionally large effective mass {dollar}rm(msp* > 100msb{lcub}e{rcub}),{dollar} along with anomalous behavior in the transport and thermodynamic properties. Among the factors contributing to this low temperature behavior are the Kondo effect, itinerant spin fluctuations, coherence effects (due to the periodic arrangement of the magnetic scatterers), crystal electric fields, and RKKY interactions. In order to understand better the low temperature properties of UBe{dollar}sb{lcub}13{rcub}{dollar}, I have studied the effects of substituting small amounts of non-magnetic Th for U ({dollar}rm Usb{lcub}1-x{rcub}Thsb{lcub}x{rcub}Besb{lcub}13{rcub}){dollar} on the resistivity, magnetoresistance, and Hall effect. These properties have been studied for 6 samples with x = 0, 0.0062, 0.0066, 0.013, 0.015, and 0.033 at temperatures from 1 K to 13 K, and for magnetic fields up to 9 Tesla. It has been found that even these small amounts of Th drastically alter the properties. Previous studies on {dollar}rm Usb{lcub}1-x{rcub}Thsb{lcub}x{rcub}Besb{lcub}13{rcub}{dollar} have been interpreted through a model which uses a low temperature coherent state of UBe{dollar}sb{lcub}13{rcub}{dollar} that is destroyed by the addition of Th. My results indicate that itinerant spin fluctuations dominate the low temperature behavior. |
