NMR studies of the original magnetic properties of cuprates: effect of impurities and defects

TL;DR

This study uses NMR to explore how impurities and defects affect the magnetic and electronic properties of cuprates, revealing local moments, AF correlations, and the impact of doping on these phenomena.

Contribution

It provides new insights into impurity-induced magnetism and AF correlations in cuprates, especially how non-magnetic impurities influence local moments and electronic behavior.

Findings

Non-magnetic impurities induce local moments on neighboring Cu sites.

AF correlations influence the oscillatory spin polarization around magnetic impurities.

Carrier scattering on spinless defects remains large even in overdoped cuprates.

Abstract

Substitutional impurities in the CuO2 planes of the cuprates allow us to probe the electronic properties of the host material. The pseudo-gap in the underdoped regime is unmodified far from the impurities even though Tc is greatly reduced. The spin polarisation induced by magnetic impurities has an oscillatory behaviour reflecting the existing AF correlations between the Cu spins. Its influence on the NMR spectra opens a way to determine the q dependence of the static spin susceptibility and the T dependence of the AF correlation length. NMR measurements demonstrate that non-magnetic impurities such as Zn induce a local moment behaviour on the neighbouring Cu sites. This magnetism revealed by spin-less sites can be understood on theoretical grounds in the case of undoped quantum spin systems, while here the carriers greatly complicate the situation. Susceptibility data show that the magnitude of the local moment decreases with increasing hole doping. This experimental evidence directly reflects the influence of AF correlations and the interference between the carriers and the Cu hole spins in the cuprates. The anomalously large scattering of the carriers on spinless defects is another indication of the originality of the electronic properties of the cuprates, which apparently extends even to the overdoped regime.