A SN-119 MOSSBAUER STUDY OF THE MAGNETIC TO NONMAGNETIC TRANSITION IN U(IN1-XSNX)3

The temperature and concentration dependence of the Sn-119 Mossbauer spectrum has been measured for U(In1-xSn(x))3. UIn3 has an antiferromagnetic transition at 91.5 K determined using both Mossbauer and specific heat measurements, and USn3 is a highly enhanced paramagnet. As Sn is substituted for In in UIn3, the Neel temperature T(N) (as determined using the temperature dependence of the magnetic susceptibility) is depressed and appears to go to zero between x = 0.4 and x = 0.5. However, the magnetic hyperfine field determined by Mossbauer spectroscopy persists to higher Sn concentration and appears to go to zero in the vicinity of x = 0.6. The difference in magnetic-nonmagnetic boundary is attributed to the presence of short-range order as the system approaches the magnetic instability. Short-range correlations in the vicinity of x = 0.6 appear to be responsible for the apparent heavy-fermion behavior previously reported for this system. In addition, the results of the Sn-119 Mossbauer studies for U(In, Sn)3 are inconsistent with the magnetic structures previously proposed to explain neutron diffraction studies and a new magnetic structure is proposed which is consistent with both the neutron and Mossbauer studies.