A SEARCH FOR THE PREDICTED MAGNETIC 5D SURFACE ATOM-W AND ATOM-RE

The magnetism of the 5d metals W and Re is investigated with the metho d of weak localization. We studied W on the surface of Au and Re on th e surface of Ag. For both systems the impurity thickness are in the ra nge between 1/100 of a monolayer (single impurities) and one monolayer . For single W and Re impurities the dephasing of weak localization is by two to three orders of magnitude smaller than that of a typical ma gnetic impurity. For the monolayers it is reduced by a factor of about five. A strong temperature dependence of the dephasing suggests that thermally activated fluctuating moments are present. A extrapolation o f this temperature dependence towards T = 0 yields no dephasing and th erefore no magnetic behavior at T = 0. Numerical calculations predicte d that W and Re impurities possess a magnetic moment of about 3.5 mu(B ) on the surface of Ag. These large moments are not found in our exper iments.