FE-57 MOSSBAUER-EFFECT IN UPDSN

Previously, the transitions to the noncollinear antiferromagnetic stru ctures accompanied by the structural distortions have been studied by a variety of X-ray, magnetic and neutron-diffraction methods. For this aim we have applied the Mossbauer effect by doping the Fe-57 isotope to UPdSn. Below T-N, except for the magnetic component, the presence o f the paramagnetic doublet with the intensity diminishing with decreas ing temperature have also been observed. As a possible reason for the occurrence of this doublet in Mossbauer spectra even far below T-N, am ong others, the fluctuation model of two magnetic phases being in ther mal equilibrium has been postulated. Moreover, we have calculated and discussed the dipolar hyperfine fields at the Pd sites (occupied also by the iron isotope) for various types of magnetic structures reported in the literature. On this basis, the so-called 'body diagonal' model of the magnetic structures of UPdSn has been found as being more prob able. We have also shown that the Mossbauer parameters exhibit an anom alous behaviour at the critical points, connected with both the struct ural and magnetic transitions which thus coincide in this compound.