237 Np Mössbauer Investigations of (U 1-x Np x ) 2 Rh 2 Sn

Abstract

Surprisingly, Np2Rh2Sn does not order magnetically whereas the uranium counterpart U2Rh2Sn orders antiferromagnetically at 24 K with a 5f moment μU≈0.38μB. We have investigated the magnetic and electronic properties of (U1−xNpx)2Rh2Sn solid solutions. For x=0.25 and 0.5, the ordering temperature decreases to 11 K whereas the Np-rich compound (x=0.75) shows the onset of magnetic order around T≈6 K. The average Np magnetic moment amounts to 0.84 μB,0.83μB and 0.25 μB respectively. The isomer shift slightly decreases, from −9.6 mm/s to −10.4 mm/s (versus NpAl2) as x increases. The values of the quadrupole interaction parameter in the ordered and paramagnetic state suggest that Np moments are parallel to c for x=0.25 and then rotate to the basal plane for higher x.