Glassy magnetic freezing of interacting clusters in LK-99-family materials

TL;DR

This study reveals that magnetization anomalies in LK-99-like materials are due to glassy magnetic freezing of clusters, not superconductivity, caused by secondary phases like covellite, emphasizing phase complexity in interpreting experimental signatures.

Contribution

It demonstrates that magnetic anomalies in LK-99 materials originate from magnetic freezing of clusters, not superconductivity, clarifying previous misconceptions about their properties.

Findings

Anomalies are reproducible across samples.

Data indicate non-superconducting magnetic glass behavior.

Covellite phase identified as the source of anomalies.

Abstract

We report reproducible magnetization anomalies appearing below room temperature in copper-doped apatite materials belonging to the LK-99 family synthesized via hydrothermal methods. These anomalies are observed consistently across samples prepared under comparable conditions. Although the extracted Mydosh parameter lies within the range often associated with vortex-glass behavior in superconductors, a detailed analysis of DC magnetization, AC susceptibility, field dependence, and magnetic memory effects demonstrates that the observed phenomena are not related to superconductivity. Instead, the data are consistent with glassy magnetic freezing of interacting clusters. Compositional and structural analysis identifies covellite (CuS), an ubiquitous secondary phase in these intrinsically multiphase materials, as the primary origin of the observed behavior. Our results clarify the magnetic origin of LK-99-related anomalies and highlight the importance of phase complexity in interpreting apparent superconducting signatures in this materials family.