89Y NMR Probe of Zn Induced Local Magnetism in YBa2(Cu(1-y)Zn(y))3O(6+x)

TL;DR

This study uses $^{89}$Y NMR to investigate how Zn substitution in YBa2Cu3O6+x induces local magnetic moments on neighboring Cu atoms, revealing impurity-induced magnetism's nature and extent in underdoped cuprates.

Contribution

It provides detailed NMR evidence of local moment formation around Zn impurities in underdoped YBCO, extending understanding of impurity effects in cuprate superconductors.

Findings

Zn induces local magnetic moments on nearby Cu atoms.

Local moments extend beyond immediate neighbors, with alternating signs.

Underdoped samples show significant impurity-induced magnetism, unlike optimally doped ones.

Abstract

We present detailed data and analysis of the effects of Zn substitution on the planar Cu site in YBa$_2$Cu$_3$O$_{6+x}$ (YBCO$_{6+x}$) as evidenced from our $^{89}$Y NMR measurements on oriented powders. For $x<<1$ 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 3$d$$^{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 $^{89}$Y $nn$ resonances are not detected, but a large $T$% -dependent contribution to the $^{89}$Y 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 $% ^{27}$Al NMR data taken on Al$^{3+}$ substituted on the Cu site in optimally doped La$_2$CuO$_4$. Further experimental work is needed to clarify the detailed evolution of the impurity induced magnetism with hole content in the cuprates.