Normal-state magnetic properties of Ni and Zn substituted in YBa ₂ Cu ₃ O _{6 + <i>x</i>} : Hole-doping dependence

Abstract

We present SQUID susceptibility data on Zn and Ni substituted\nYBa_{2}Cu_{3}O_{6+x}. Cross-checks with NMR yield an unprecedented accuracy in\nthe estimate of the magnetic susceptibility associated with the substituants,\nfrom the underdoped to the lightly overdoped case. This allows us to determine\nthe Weiss temperature \\theta for YBCO: its value is very small for all hole\ndopings n_h. Since in conventional metals, the Kondo temperature,\n$T_{K}&lt;\\theta$, magnetic screening effects would not be expected for $T\\gg\n\\theta$; in contrast, increasing n_h produces a reduction of the small moment\ninduced by Zn^{2+} and a nearly constant effective moment for Ni^{2+}\ncorresponding to a spin 1/2 rather than to a spin 1.\n