Positron lifetime measurements and electronic structure of CeNiSn

Abstract

Positron lifetime measurements have been carried out in CeNiSn, in the temperature range of 5 to 300 K. In the 300 and 150-K temperature interval the positron lifetime is seen to decrease from 178±1 to 176±1 ps. Below 150 K the lifetime shows a gradual increase and attains a value of 181±1 ps at 35 K, below which the lifetime shows a small decrease. This behavior of the positron lifetime is seen to correlate with earlier measurements [Y. Uwamoto et al., J. Magn. Magn. Mater. 104, 643 (1992)] on the thermal expansion coefficient in CeNiSn, which has been understood in terms of electronic structure changes associated with the system transforming from an independent Kondo regime to a Kondo insulating state, via an intermediate mixed valent regime. Strong support for these electronic structure changes are provided by ab initio positron lifetime calculations which are seen to be in good agreement with the Positron experiments.