ENHANCED SN-119 MOSSBAUER QUADRUPOLE INTERACTIONS BELOW THE MAGNETIC PHASE-TRANSITION OF UPT2SN

Sn-119 Mossbauer effect measurements (4.2 K < T < 300 K) have been per formed on the antiferromagnetic (AF) intermetallic compounds UPt2Sn an d UCu2Sn. For temperatures above T-N we find that the quadrupole split ting (Delta E-Q) in UPt2Sn is about 3 times larger than in UCu2Sn. Thi s difference in Delta E-Q is suggested to be due to a large electronic contribution from the Pt-ligands in UPt2Sn. Upon decreasing temperatu re below T-N, we find only in UPt2Sn an anomalous increase of Delta E- Q relative to the extrapolated Delta E-Q values in the paramagnetic ph ase (4% increase at 4.2 K). In addition, we have measured the thermal expansion coefficient (alpha) of a polycrystalline UPt2Sn sample (4.2 K < T < 200 K) using a high-resolution capacitive dilatometer. We find a jump in alpha at T-N of Delta alpha approximate to 1.1 x 10(-6) K-1 . It is shown that the enhancement of Delta E-Q is of electronic origi n and related to the onset of AF order in UPt2Sn.