EFFECT OF MAGNETIC-FIELDS ON THE KONDO INSULATOR CERHSB - MAGNETORESISTANCE AND HIGH-FIELD HEAT-CAPACITY MEASUREMENTS

The compound CeRhSb is a mixed valent Ce-based compound which shows a gap in the electronic density of states at low temperatures. The gap m anifests by a rise in electrical resistivity-below about 8 K from whic h the gap energy is estimated to be about 4 K. We have carried out hea t capacity measurements on this compound in various applied fields up to 9.85 T. The magnetic contribution to the heat capacity, Delta C, is found to have a maximum in Delta C/T vs T at 10 K, below which Delta C/T is linear with T. This is attributed to the fact that below this t emperature, in the gapped state, the electronic density of states decr eases linearly with decreasing temperature. On application of a magnet ic field, the electronic specific heat coefficient gamma in the gapped state increases by similar to 4 mJ/mol K-2. The maximum in Delta C/T vs T is observed in all fields, which shifts to lower temperatures sim ilar to 1 K at 5.32 T and raises again at 9.85 T to about the same val ues as at H=0 T. This suggests that the gap exists for all fields up t o 9.85 T. Above 10 K, in the mixed-valent state, Delta C/T vs T decrea ses with increasing temperature in zero field. There is hardly any eff ect of application of field in the mixed-valent state, since the appli ed fields are too small to change the already large density of states at the Fermi level. We have also carried out magnetoresistance measure ments on CeRhSb up to fields of 5.5 T at 2, 4.5, 10, 20, and 30 K. The magnetoresistance in CeRhSb is positive at temperatures of 4.5 K and above, in applied fields up to 5.5 T. At 5.5 T, the magnetoresistance is maximum at 4.5 K (6%) and decreases with increasing temperature. Th e observation of the maximum is consistent with the observation of a m aximum in Delta C/T vs T and is due to a change in the density of stat es. At a temperature of 2 K, a negative magnetoresistance is observed for magnetic fields greater than similar to 3.5 T which suggests reduc tion in the gap.