MAGNETIC-SUSCEPTIBILITY OF PR2-XCEXCUO4 MONOCRYSTALS AND POLYCRYSTALS

We measured the temperature dependence of the magnetic susceptibility of Pr2-xCexCuO4 monocrystals and polycrystals in the composition range x = 0-0.18. For all compositions, the susceptibility curves reveal strong crystal-field effects and are evaluated in terms of Van Vleck's equation for magnetic susceptibility. At temperatures above 100 K, the behavior could be described by a Curie-Weiss-like equation, the parameters of which allow us to characterize the crystal-field interactions. The concentration dependence of these parameters is much stronger in the monocrystals, with the apparent magnetic moment going through a sharp maximum near x = 0.1, the composition of the onset of superconductivity after a reducing anneal. The concentration dependence of the magnetic moment can be qualitatively interpreted as a contribution of charge-carrying spins in localized states, mainly through initiating Cu2+-Pr3+ interactions. With increasing Ce, these additional spins can not remain localized, thus the magnetic moment decreases, and a reducing anneal results in superconductivity.