We have investigated the transport properties of high-quality ${\mathrm{Nd}}_{1.78}$${\mathrm{Ce}}_{0.22}$${\mathrm{CuO}}_{4\pm \mathrm{\delta }}$ films as a function of oxygen concentration. Surprisingly we find superconductivity in films that are slowly cooled in vacuum from the deposition temperature. A systematic study of the effect of oxygen on resistivity, Hall effect, and thermopower suggests that extra oxygen introduces impurity scattering without changing the carrier density. Magnetoresistance data reveal that these impurities are spin disordered in nature. The spin impurities introduced upon oxygenation of the sample may be responsible for suppressing the superconductivity. © 1996 The American Physical Society.

• Received 16 June 1995

DOI:https://doi.org/10.1103/PhysRevB.53.871