Dynamic correlated Cu(2) magnetic moments in superconducting YBa_2(Cu_0.96Co_0.04)_3O_y (y ~ 7)

TL;DR

This study investigates the coexistence of dynamic magnetic moments and superconductivity in a copper-oxide compound, revealing that magnetic correlations fluctuate too rapidly for certain measurement techniques to detect.

Contribution

It provides evidence of dynamic Cu(2) magnetic moments coexisting with superconductivity in YBa_2(Cu_0.96Co_0.04)_3O_y, highlighting the importance of measurement timescales.

Findings

Magnetic reflections indicate antiferromagnetic Cu(2) structure with T_N ~ 400 K.

Muon spin relaxation does not detect static magnetic order.

Magnetic moments fluctuate rapidly, coexisting with superconductivity.

Abstract

We have examined the magnetic properties of superconducting YBa_2(Cu_0.96Co_0.04)_3O_y (y ~ 7, T_sc = 65 K) using elastic neutron scattering and muon spin relaxation (muSR) 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 Neel temperature T_N ~ 400 K. This magnetically correlated state is not evidenced by the muSR measurements. We suggest 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 muSR measurements, at least down to ~ 50 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.