Electrical-transport of YBA2(CU1-XCOX)3O7+DELTA - a kondo type behavior

New data on resistivity and thermopower for YBa2(Cu1-xCo(x)3O7+delta (0 less-than-or-equal-to x less-than-or-equal-to 0.12) over an extended temperature range 20-600K has been used to study systematically the effect of transition metal impurities in the YBa2Cu3O7(Y123) system. In order to distinguish between possible scattering mechanisms the data has been fitted to theoretical results based on Mott and Kondo models. Although resistivity can be fitted reasonably well to both models the thermopower clearly favour a Kondo model. The results suggest that the antiferromagnetic spin correlations between conduction electron and localised moments associated with 3d ions play a prominent role in this system

ELECTRICAL-TRANSPORT AND MAGNETIC STUDIES OF ND1-XCAXSR2CU2FEO-DELTA COMPOUNDS

We have measured the temperature dependence of the DC electrical resistivity and susceptibility in the interval 4.2-300 K for Nd1-xCaxSr2Cu2FeOδ (x = 0.0, 0.1, 0.2 and 0.3). Analysis of the results showed the density of states to be a strong function of x, indicating the existence of short range fluctuations near the Fermi level EF. The magnetic susceptibility, however, shows the oxidation state of Fe remains at +3 for x ≥ 0. © 1994.status: publishe