MAGNETISM OF FE, NI, AND ZN IN ND1.85CE0.15CUO4 - COMPARISON OF EXPERIMENT AND THEORY

We have studied the magnetic and superconducting properties of Fe-, Ni -, and Zn-substituted Nd1.85Ce0.15CuO4 bulk materials. The normal-stat e magnetic susceptibility of all samples is found to follow the Curie- Weiss law between 50 and 300 K. The magnitude of local moments deduced for Fe and Ni are 2.2 mu(B) and 2 mu(B), respectively. The observed m oment on Ni is attributed to Ni in a 3+ valency state. A magnetic mome nt of 0.8 mu(B) is obtained in Zn-substituted samples. This is ascribe d to the localized Cu2+ spins. The T-c vs 3d ion concentration (x) cur ves indicate that Ni inhibits the T-c of this system at an anomalously higher rate. In an effort to understand the correlation between the m agnitude of the magnetic moment on the 3d ion and its role in the supp ression of superconductivity, we have performed density-functional clu ster calculations under local-spin-density approximations. The calcula tions support the following inferences drawn from the experiments: (i) Ni is in a 3+ state, (ii) the moment of 0.8 mu(B) observed in Zn-subs tituted samples is due to localized Cu2+ spins, and (iii) Zn induces a moment of almost the same magnitude in both the electron-doped and th e hole-doped La1.85Sr0.15CuO4 systems. We have also attempted to expla in qualitatively the observed T-c vs x behavior in the above systems u sing the effective single-band t-J model.