The magnetic properties of heavy-fermion superconductors. UPd2Al3 and URu2S
i2, were studied by U-238 Mossbauer spectroscopy to elucidate the local ele
ctronic stares of uranium atoms directly. In the paramagnetic states of UPd
2Al3 and URu2Si2, we have observed an appreciable change in lint width caus
ed by the paramagnetic relaxation, which is the evidence for the formation
of the heavy fermion. (C) 2000 Elsevier Science B.V. All rights reserved.