ANISOTROPY AND 2 LENGTH SCALES IN THE MAGNETIC CRITICAL SCATTERING INTHE HEAVY-FERMION SUPERCONDUCTOR UPD2AL3

We have performed neutron critical scattering experiments on the heavy -fermion superconductor UPd2Al3 above the Neel temperature in order to characterize the short-ranged correlations associated with the magnet ic ordering. The magnetic correlation length along the hexagonal c axi s is longer than that in the basal plane, suggesting that the antiferr omagnetic interaction along the c axis is stronger than the ferromagne tic one in the basal plane. This antiferromagnetic correlation is disc ussed in connection with the pairing mechanism of the superconductivit y. We also find that the magnetic fluctuations exhibit the two-length scales reminiscent of features observed in Tb and Ho.