Abstract
As a microbe of the environment, 20--30 ppm of $^{57}\mathrm{Co}$ is substituted for Cu in the ${\mathrm{CuO}}_{2}$ planes of ${\mathrm{Nd}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ce}}_{\mathit{x}}$${\mathrm{CuO}}_{4}$. M\"ossbauer effect studies show that all the oxygenated and ``deoxygenated'' samples with x=0.00, 0.14, 0.16, and 0.18 contain large proportions of micro spin clusters. Even in the deoxygenated ceramic with x=0.16, superconducting regions coexist with about 53% of microscopic spin clusters of tyical size \ensuremath{\sim}25--250 \AA{}. Spin clusters formation is induced by extraneous oxygen. 2D magnetic order in the electron-doped system is much stronger than that in systems hole-doped, with extremely long-lived (>${10}^{\mathrm{\ensuremath{-}}8}$ s) spin correlations far above the 3D N\'eel temperature.
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