1 1 9Sn Mössbauer study of the evolution of the magnetic state in U(Sn,Pb)3

Abstract

USn3 is a highly enhanced paramagnet that is very near a magnetic instability, and UPb3 has an antiferromagnetic transition at 31.3 K. As Sn is substituted for Pb in U(Sn1−xPbx)3, the Néel temperature, TN, initially increases to 38 K at x=0.7, then decreases, and appears to go to zero for x≲0.1. The temperature dependence of the magnetic susceptibility for 0≤x≤1.0 and 119Sn Mössbauer spectra for 0≤x≤0.98 have been measured. The Mössbauer spectra indicate that the antiferromagnetic structure for the Pb-rich pseudobinary alloys is not type I as previously reported. As x decreases, at least two, and possibly four, distinct Sn hyperfine field sites are found. The saturation hyperfine fields at the Sn sites do not show as pronounced a variation with concentration as is seen in TN. For larger x the saturation hyperfine fields are independent of x, which suggests that the U magnetic moments are nearly constant for the Pb-rich pseudobinary alloys, and then drop rapidly to zero at the magnetic instability. The fraction of Sn sites seeing a particular hyperfine field is observed to vary monotonically across the series.