Y-89 NMR probe of Zn induced local magnetism in YBa2(Cu1-yZny)(3)O6+x
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We present detailed data and analysis of the effects of Zn substitution on the planar Cu site in YBa2Cu3O6+x (YBCO6+x) as evidenced from our Y-89 NMR measurements on oriented powders. For x much less than 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 YBCO6+x. For optimally doped compounds Y-89 nn resonances are not detected, but a large T-dependent contribution to the Y-89 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 per formed on YBCO6+x samples prepared specifically in order to minimize the content of impurity phases. We find significant differences between the present results on the underdoped YBCO6+x samples and Al-27 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.
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