X-RAY-ABSORPTION EDGE SHIFTS IN RARE-EARTH-TRANSITION-METAL COMPOUNDS

X-ray-absorption K-edge shifts of cobalt have been measured in Y2Co17, YCo5, and YCo3 compounds whose crystal structures are derivatives of the CaCu5 structure. The edge shifts vary monotonically with the Y:Co ratio. We compare them with Fe, Y, and Ce edge shifts determined for s everal other related materials, including Y2Fe17, Ce2Fe17, and CeCo2. In all cases, the shifts are the same sign, a fact that points to the absence of a significant uncompensated charge transfer from one elemen tal constituent to another. Identifying the edge shifts as core-level shifts, we find that the Watson-Hudis-Perlman charge-compensation mode l is applicable to these systems; estimates of the model parameters le ad to small net charge transfers consistent with available Mossbauer e ffect measurements. Our results show that there is no straightforward relation between the transition-metal magnetic moment and either charg e transfer or corresponding absorption edge shift, which implies that the variation of the moment with stoichiometry in these materials is n ot governed by the filling of rigid transition-metal bands.