Dynamic correlated Cu(2) magnetic moments in superconductingYBa2(Cu0.96Co0.04)3Oy(y∼7)

Abstract

We have examined the magnetic properties of superconducting ${\text{YBa}}_{2}{({\text{Cu}}_{0.96}{\text{Co}}_{0.04})}_{3}{\text{O}}_{y}(y\ensuremath{\sim}7,{\text{T}}_{sc}=65\text{ }\text{K})$ using elastic neutron scattering and muon spin relaxation $(\ensuremath{\mu}\text{SR})$ on single-crystal samples. The elastic-neutron-scattering measurements evidence magnetic reflections, which correspond to a commensurate antiferromagnetic Cu(2) magnetic structure with an associated N\'eel temperature ${T}_{\text{N}}\ensuremath{\sim}400\text{ }\text{K}$. This magnetically correlated state is not evidenced by the $\ensuremath{\mu}\text{SR}$ measurements. We suggest that this apparent anomaly arises because the magnetically correlated state is dynamic in nature. It fluctuates with rates that are low enough for it to appear static on the time scale of the elastic-neutron-scattering measurements, whereas on the time scale of the $\ensuremath{\mu}\text{SR}$ measurements, at least down to $\ensuremath{\sim}50\text{ }\text{K}$, it fluctuates too fast to be detected. The different results confirm the conclusions reached from work on equivalent polycrystalline compounds: the evidenced fluctuating, correlated Cu(2) moments coexist at an atomic level with superconductivity.