Direct Search for a Ferromagnetic Phase in a Heavily Overdoped Nonsuperconducting Copper Oxide

TL;DR

This study investigates the presence of ferromagnetic phases in heavily overdoped, nonsuperconducting copper oxides, revealing dilute static magnetic moments that support weak localized ferromagnetism predictions.

Contribution

It provides direct experimental evidence of dilute static magnetic moments in overdoped copper oxides, constraining the nature of possible ferromagnetic phases in this regime.

Findings

Detection of static magnetic moments at low temperature in overdoped samples

Magnetism appears as dilute static moments, not long-range order

Results support weak localized ferromagnetism at high doping levels

Abstract

The doping of charge carriers into the CuO2 planes of copper oxide Mott insulators causes a gradual destruction of antiferromagnetism and the emergence of high-temperature superconductivity. Optimal superconductivity is achieved at a doping concentration p beyond which further increases in doping cause a weakening and eventual disappearance of superconductivity. A potential explanation for this demise is that ferromagnetic fluctuations compete with superconductivity in the overdoped regime. In this case a ferromagnetic phase at very low temperatures is predicted to exist beyond the doping concentration at which superconductivity disappears. Here we report on a direct examination of this scenario in overdoped La2-xSrxCuO4 using the technique of muon spin relaxation. We detect the onset of static magnetic moments of electronic origin at low temperature in the heavily overdoped nonsuperconducting region. However, the magnetism does not exist in a commensurate long-range ordered state. Instead it appears as a dilute concentration of static magnetic moments. This finding places severe restrictions on the form of ferromagnetism that may exist in the overdoped regime. Although an extrinsic impurity cannot be absolutely ruled out as the source of the magnetism that does occur, the results presented here lend support to electronic band calculations that predict the occurrence of weak localized ferromagnetism at high doping.