Emerging Diluted Ferromagnetism in High-T_c Superconductors Driven by Point Defect Clusters

Area of Science:

• Materials Science
• Condensed Matter Physics
• Superconductivity

Background:

• Defects in ceramics are typically detrimental.
• However, in complex oxides like Yttrium Barium Copper Oxide (YBa₂Cu₃O_7-δ), defects can enhance properties and reveal novel physics.
• Nanoscale defects in Y123 are known to immobilize magnetic flux vortices.

Purpose of the Study:

• To investigate previously unforeseen point defects in Y123 thin films.
• To understand the nature of these defects and their impact on superconducting properties.
• To explore the phenomenon of defect-driven ferromagnetism in Y123.

Main Methods:

• Aberration-corrected scanning transmission electron microscopy (STEM) for atomic-level structural and chemical analysis.
• Density functional theory (DFT) calculations to model defect behavior and ferromagnetism.
• X-ray magnetic circular dichroism (XMCD) to detect and characterize magnetic moments.

Main Results:

• Discovery of point defects within Y123 thin films leading to embedded ferromagnetic clusters.
• Atomic-scale imaging revealed the structure and chemistry associated with these defects.
• DFT calculations provided insights into the defect nature and predicted defect-driven ferromagnetism.
• XMCD confirmed the presence of aligned Copper (Cu) magnetic moments below the superconducting critical temperature.

Conclusions:

• Point defects in Y123 can induce ferromagnetism, forming dilute magnetic clusters.
• This defect-driven ferromagnetism coexists with superconductivity, challenging previous understandings.
• The findings open new avenues for exploring defect engineering in complex oxides.