Antiferromagnetic properties of a water vapor-inserted $YBa_2Cu_3O_{6.5}$ compound studied by NMR, NQR and $\mu$ SR

TL;DR

This study investigates the antiferromagnetic phases formed in water vapor-inserted YBa2Cu3O6.5 using NMR, NQR, and μSR, revealing non-superconducting magnetic states with ordered Cu spins and similar Néel temperatures to undoped compounds.

Contribution

It provides detailed experimental evidence of water-induced antiferromagnetic phases in YBa2Cu3O6.5, highlighting the role of Cu(1) chains and the impact of water insertion on magnetic properties.

Findings

Water insertion transforms NQR spectra and induces antiferromagnetic phases.

Proton NMR detects two static internal field sites at 150 and 15 Gauss.

Muon sites show similar local fields that vanish near 400 K.

Abstract

We present a detailed NQR, NMR and $\mu $SR study of a magnetic phase obtained during a topotactic chemical reaction of YBa$_{2}$Cu$_{3}$O$_{6.5}$ high- temperature superconductor with low-pressure water vapor. Our studies give straightforward evidence that the ''empty'' Cu(1) chains play the role of an easy water insertion channel. It is shown that the NQR spectrum of the starting material transforms progressively under insertion of water, and completely disappears when one H$_{2}$O molecule is inserted per unit cell. Similarly, a Cu ZFNMR signal characteristic of this water inserted material appears and grows with increasing water content, which indicates that the products of the reaction are non-superconducting antiferromagnetic phases in which the bilayers are ordered. These antiferromagnetic phases are felt by proton NMR which reveals two sites with static internal fields of 150 and about 15 Gauss respectively. Two muon sites are also evidenced with similar local fields which vanish at $T\approx 400$ K. This indicates that the magnetic phases have similar N\'{e}el temperatures as the other bilayer undoped compounds. An analysis of the internal fields on different sites of the structure suggests that they can be all assigned to a single magnetic phase at large water content in which the Cu(1) electron spins order with those of the Cu(2). It appears that even samples packed in Stycast epoxy resin heated moderately at a temperature (200$^{0}$C) undergo a reaction with epoxy decomposition products which yield the formation of the same final compound. It is then quite clear that such effects should be considered quite seriously and avoided in experiments attempting to resolve tiny effects in such materials, as those performed in some recent neutron scattering experiments.