POSITRON-ANNIHILATION STUDIES IN CENIIN AND LANIIN

Doppler broadened positron annihilation spectral lineshape (DBPAS) and positron lifetime measurements in the temperature range 18-280 K have been performed in CeNiIn and LaNiIn systems. The nature of the temper ature variations of the lifetime in both systems is almost similar in the whole temperature range studied, whereas the nature of the tempera ture variation of the S parameter in CeNiIn is similar to that in LaNi In except in the temperature region 18-40 K. For the former system the re is a dip around 20 K in the S parameter versus temperature curve. T he lifetime versus T curve in both systems could be explained by the t hermal expansion of the lattice. The S parameter versus T curve in LaN iIn could also be attributed to the thermal expansion of the lattice, whereas in CeNiIn the above mentioned dip seems an extra feature of th e thermal expansion of the lattice. To understand this low temperature behaviour other results on the same system have been discussed.