Absence of the impurity-induced magnetic order in the electron-doped high-Tc cuprates Pr0.86LaCe0.14Cu1−y(Zn, Ni)yO4

Zero-field muon-spin-relaxation measurements have been carried out in order to investigate the Zn- and Ni-substitution effects on the Cu-spin dynamics in the electron-doped Pr0.86LaCe0.14Cu1−y(Zn, Ni)yO4+α−δ with y = 0, 0.01, 0.02, 0.05 and different values of the reduced oxygen content δ (δ ≦  0.09). For the samples with y = 0 and very small δ values of δ < 0.01, a muon-spin precession due to the formation of a long-range antiferromagnetic order has been observed at low temperatures below ∼5 K. For the moderately oxygen-reduced samples of 0.01 ≦ δ ≦ 0.09, on the contrary, no muon-spin precession has been observed and the temperature dependence of the spectra is similar to one another regardless of the y value. That is, no impurity-induced slowing down of the Cu-spin fluctuations has been detected, which is very different from the results of the hole-doped high-Tc cuprates. The reason is discussed.