Impact of the reduction process on the long-range antiferromagnetism inNd1.85Ce0.15CuO4

We have performed an ultrasonic study of ${\mathrm{Nd}}_{2\ensuremath{-}x}{\mathrm{Ce}}_{x}\mathrm{Cu}{\mathrm{O}}_{4}$ samples which show frequency-dependent ultrasonic anomalies below $10\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ in both the ${\mathrm{C}}_{66}$ elastic moduli and the corresponding attenuation $\ensuremath{\alpha}$ similar to those observed in the undoped material. While the cerium doping only changes the temperature and magnetic scales over which the anomalies are detected, no anomaly is observed for the reduced and superconducting state of a ${\mathrm{Nd}}_{1.85}{\mathrm{Ce}}_{0.15}\mathrm{Cu}{\mathrm{O}}_{4}$ sample. This indicates that the sudden suppression of the ${\mathrm{Cu}}^{2+}$ long-range three-dimensional antiferromagnetic order following the reduction process favors the emergence of the competing superconducting state.