O-17 NMR measurements of the width of the line of the CuO2 planes were
performed in underdoped YBaCuO samples with Zn and Ni substitution. C
ontrary to the usual observation in optimally doped compounds, the imp
urity induced widths are found to deviate markedly from a 1/T Curie la
w. An interpretation is given in terms of a temperature dependence of
the static susceptibility chi'(q) of the pure compound near Q(AF).