The magnetic phase diagram of ${\mathrm{Nd}}_{1.85}{\mathrm{Ce}}_{0.15}{\mathrm{CuO}}_{4+\delta }$ has been investigated up to oxygen content $\delta \simeq \mathrm{0.064.}$ Magnetization, susceptibility, and muon spin relaxation experimental data show that an unconventional spin-glass (SG) phase sets in for $\delta \gtrsim \mathrm{0.06.}$ A well defined SG-like transition occurs at $T_g\simeq 5\mathrm{K}$ for the compound with maximum oxygen content. Below $T_g,$ however, the shape of susceptibility curves as well as the ${\mathrm{\mu }}^{+}$-polarization recovery laws point out the persistence of residual spin-fluctuations, a signature of a noncomplete freezing of the magnetic lattice. These experimental evidences can be explained by assuming two different slowing down processes for the fluctuations of the Cu and Nd spin ensembles. A phase diagram which agrees with the main results on other $\mathrm{h}\mathrm{i}\mathrm{g}\mathrm{h}-T_c$ cuprates is reported.

• Received 27 May 2003

DOI:https://doi.org/10.1103/PhysRevB.68.104524