ANNIHILATION OF SUPERCONDUCTIVITY BY CO SUBSTITUTION FOR CU IN ND1.85CE0.15CUO4

The effect of Co substitution for Cu in the Nd1.85Ce0.15Cu1-xCoxO4 system has been investigated by powder x-ray-diffraction analysis and resistivity and magnetic susceptibility measurements. It is observed that only 0.6 at Co substitution for Cu destroys the superconductivity of the sample. For heavily doped samples (with x0.01), the effective magnetic moment per Co ion is found to decrease with increasing x. The antiferromagnetic correlation between doped Co ions is also discovered to increase with increasing x. For lightly doped samples (with 0.008), the dependence of Tc on x may be caused by a pair-breaking effect. The absolute value of the exchange interaction energy between a Co2+ ion and an electron is estimated at 0.09 eV for S=3/2 or 0.19 eV for S=1/2, where S is the total spin of a Co2+ ion. © 1990 The American Physical Society.