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

In YBa2Cu3O7, the substitution of copper atoms by transition metals has been extensively studied experimentally. Their influence on T(c) has been measured by many workers and also the value of the magnetic moment associated with the impurities deduced from susceptibility measurements. Using a semi-empirical tight-binding calculation, including s, p and d copper orbitals and p oxygen orbitals, we have obtained the density of states for a perfect crystal of YBa2Cu3O7. We use the recursion method to calculate Green functions and densities of states. The perturbation associated with the impurity is represented by a diagonal matrix element determined with the Friedel sum rule, and a modification of the first neighbours interactions. The spin polarisation is introduced with a Stoner relation. The results confirm that the impurities in the middle of the series are the most magnetic ones. The value obtained for iron is satisfactory, but for manganese it is too high. The estimates of the magnetic moments are compared to a recent small cluster calculation and to experimental results.