Magnetic Properties of the Heavy Fermion System URANIUM-BERYLLIUM-13.

UBe_{13} is one of the heavy fermion superconductors with an unusually large electronic specific heat and an unconventional magnetic susceptibility. The magnetization in both the normal and mixed states of UBe_{13} has been measured in magnetic fields up to 19 Tesla and temperatures down to 50mK. For high fields and low temperatures, two types of capacitive DC magnetometers, a cantilever (CMAG) and a diaphragm (DMAG) magnetometer, have been developed. These are at present the only DC magnetometers which work simultaneously in a dilution refrigerator and a resistive Bitter magnet. In the normal state the magnetization at temperatures above T_{c} shows a slight deviation from simple linear behavior. Below T_{c }, however, the magnetization shows an unusual upturn at fields greater than 14T, which may be explained by field induced spin fluctuation or SDW transition. In the mixed state of UBe_{13}, a large and time-dependent hysteresis in the magnetization curve has been observed. This time dependence is well -described by an exponential decay, and the relaxation time is strongly dependent on temperature and magnetic field. Two different temporal responses corresponding to regimes above and below a crossover point in the hysteresis loops are found. This hysteresis has been shown to be due to anisotropic flux penetration. The magnetization curve in the superconducting mixed state is evidence of anisotropic superconductivity in UBe_{13}. The two regimes in the hysteresis loops support the suggestion that there exist two order parameters or two domain formations of the flux lattice in UBe_{13} . For comparison the time dependence of the magnetization of BiPb has been measured.