89Y NMR probe of Zn induced local magnetism in YBa2(Cu1-yZny) 3O6+x

We present detailed data and analysis of the effects of Zn substitution on the planar Cu site in YBa₂Cu₃O_6+x (YBCO_6+x) as evidenced from our ⁸⁹Y NMR measurements on oriented powders. For x << 1x \ll 1 we find additional NMR lines which are associated with the Zn substitution. From our data on the intensities and temperature dependence of the shift, width, and spin-lattice relaxation rate of these resonances, we conclude that the spinless Zn 3d ¹⁰ state induces local moments on the near-neighbour (nn) Cu atoms. Additionally, we conjecture that the local moments actually extend to the farther Cu atoms with the magnetization alternating in sign at subsequent nn sites. We show that this analysis is compatible with ESR data taken on dilute Gd doped (on the Y site) and on neutron scattering data reported recently on Zn substituted YBCO_{6 + x}. For optimally doped compounds ⁸⁹Y nn resonances are not detected, but a large T-dependent contribution to the ⁸⁹Y NMR linewidth is evidenced and is also attributed to the occurence of a weak induced local moment near the Zn. These results are compatible with macroscopic magnetic measurements performed on YBCO_{6 + x} samples prepared specifically in order to minimize the content of impurity phases. We find significant differences between the present results on the underdoped YBCO_{6 + x} samples and ²⁷Al NMR data taken on Al³⁺ substituted on the Cu site in optimally doped La₂CuO₄. Further experimental work is needed to clarify the detailed evolution of the impurity induced magnetism with hole content in the cuprates.