Predicted Ferromagnetism in Discovered Co-Bi Binary Phases.

Area of Science:

• Solid-state materials science
• Magnetism and electronic properties
• High-pressure synthesis and characterization

Background:

• Binary solid-state materials are crucial for understanding magnetism and electronic properties.
• Cobalt (Co) and Bismuth (Bi) offer a compelling combination for exploring spin-orbit coupling and magnetism.
• Previous research indicated superconductivity in high-pressure Co-Bi phases.

Purpose of the Study:

• To investigate the cobalt-bismuth (Co-Bi) system for new ferromagnetic materials.
• To discover novel candidates for permanent magnets by combining theoretical and experimental approaches.
• To explore the potential for Co-Bi compounds to exhibit both magnetism and superconductivity.

Main Methods:

• Utilized ab initio random structure searching calculations to predict new Co-Bi compounds.
• Employed experimental high-pressure synthesis to create and identify Co-Bi phases.
• Combined theoretical predictions with experimental validation for structure discovery.

Main Results:

• Identified five new Co-Bi compounds computationally, with diverse structural motifs.
• Experimentally synthesized four Co-Bi phases: α-CoBi, α-CoBi2, β-CoBi, and β-CoBi2.
• Confirmed three synthesized phases (α-CoBi2, β-CoBi, β-CoBi2) matched theoretical predictions, achieving a 60% success rate.
• Theoretical calculations predicted β-CoBi and β-CoBi2 to be ferromagnetic.
• β-CoBi demonstrated higher magnetocrystalline anisotropy energy compared to established permanent magnets like CoPt and Nd-Fe-B.

Conclusions:

• The Co-Bi system is a promising platform for discovering new magnetic materials.
• The combination of theoretical calculations and experimental synthesis is effective for identifying novel compounds.
• Ferromagnetic Co-Bi phases, particularly β-CoBi, show potential for advanced permanent magnet applications.