ELECTRONIC-STRUCTURE OF IMPURITIES OF THE 1ST TRANSITION SERIES IN YBA2CU3O7

In YBa2Cu3O7, the substitution of copper atoms by transition metals ha s been extensively studied experimentally. Their influence on T(c) has been measured by many workers and also the value of the magnetic mome nt associated with the impurities deduced from susceptibility measurem ents. Using a semi-empirical tight-binding calculation, including s, p and d copper orbitals and p oxygen orbitals, we have obtained the den sity of states for a perfect crystal of YBa2Cu3O7. We use the recursio n method to calculate Green functions and densities of states. The per turbation associated with the impurity is represented by a diagonal ma trix element determined with the Friedel sum rule, and a modification of the first neighbours interactions. The spin polarisation is introdu ced with a Stoner relation. The results confirm that the impurities in the middle of the series are the most magnetic ones. The value obtain ed for iron is satisfactory, but for manganese it is too high. The est imates of the magnetic moments are compared to a recent small cluster calculation and to experimental results.