Magnetic properties of ${\mathrm{NdNi}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Co}}_{\mathit{x}}$${\mathrm{O}}_3$ samples: Evidence of spin-glass behavior

${\mathrm{NdNi}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Co}}_{\mathit{x}}$ ${\mathrm{O}}_3$ perovskites with 0.3≤x≤0.8 show a peak anomaly at low temperatures (≊28 K) in their ${\mathrm{\chi }}_{\mathrm{ac}}$(T) curve. The frequency dependence of the peak anomaly and magnetization experiments after different thermal cycles, i.e., cooling the samples in the presence of a magnetic field or zero-field cooling, shows that the anomaly is associated with magnetic relaxation processes indicating a new spin-glass transition. X-ray diffraction, transmission electron microscopy, and analysis of the magnetic data agree with the absence of small magnetic impurities which could give smaller relaxation phenomena. A discussion of the microscopic origin of such behavior has also been given.