Highlights

• MnBi alloys demonstrate exceptional magnetic properties:
  
  
  
  • High coercivity up to 23 kOe
  
  
  • Positive temperature coefficient
  
  
  • Energy products reaching 25 MGOe with exchange coupling
  
  
  
  

  These properties make them leading rare-earth-free permanent magnet candidates.

  
  
• Despite promising lab results, manufacturing MnBi at an industrial scale faces critical barriers, including:
  • Phase instability
  • Complex production requirements
  • Difficulty scaling thin-film and nanoparticle methods beyond research settings
• Even if MnBi advances commercially, China's 90% control of rare earth magnet processing maintains their supply chain dominance unless Western nations invest in midstream refining and manufacturing capacity.

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A comprehensive review of MnBi alloys rekindles hopes for non-rare-earth magnets — but also underscores barriers that keep China dominant in the global magnet supply chain.

Central Institute of Technology Kokrajhar

A major new review in Next Materials by B. Mallik and S.K. Srivastava both with the Department of Physics, Central Institute of Technology Kokrajhar (opens in a new tab), Kokrajhar, India, takes a deep and timely look at manganese–bismuth (MnBi) alloys—one of the most promising rare-earth-free permanent magnet candidates. Drawing from nearly a century of research and a surge of recent thin-film and nanoparticle work, the authors conclude that MnBi combines high coercivity, strong thermal stability, and a positive temperature coefficient—a rare combination sought after in electric vehicles, renewable energy systems, and aerospace technologies.

Yet the review also highlights a stark reality: manufacturing MnBi at an industrial scale remains extremely difficult, and even if MnBi advances commercially, China’s near-total dominance of rare earth processing will continue shaping strategic outcomes.

Study Methods: A Sweeping, Technology-Focused Review

Mallik and Srivastava conducted a comprehensive literature synthesis spanning:

• Thin-film deposition (MBE, sputtering, PLD)
• Melt-spinning, mechanical alloying, electrodeposition, reactive sintering
• Nanoparticle production through cryo-milling and wet chemistry
• Magnetic analyses across temperature, composition, crystallinity, grain size
• Hard–soft exchange-coupled bilayers (MnBi/FeCo, MnBi/Co)
• Comparative cost and performance modelling

For non-specialists, this was not a single experiment but a state-of-the-science review: a map of how MnBi behaves, how it can be synthesized, and where it may (or may not) fit into future magnet markets.

Key Findings: Why MnBi Is Back in the Spotlight

1. MnBi has genuinely attractive magnetic properties

The low-temperature phase (LTP-MnBi) delivers:

• High coercivity: ~19 kOe (thin films), 20–23 kOe (nanoparticles)
• Strong magnetocrystalline anisotropy: ~1.6×10⁶ J/m³
• Positive temperature coefficient: enhanced stability at high temperatures
• Saturation magnetization: 70–80 emu/g in optimized films
• Theoretical (BH)max: ≈ 20 MGOe

While below modern NdFeB (≈40–50 MGOe), MnBi easily outperforms ferrites and at far lower material cost.

2. Thin films deliver the strongest performance

With ideal crystal orientation and precise Mn/Bi ratios, thin films achieve up to 16.3 MGOe.

3. Exchange coupling nearly doubles performance

By layering MnBi with soft magnetic phases (FeCo, Co, Fe₃C@C, FeNi@C), energy products reach 21–25 MGOe—approaching entry-level rare-earth magnets.

4. Nanoparticles provide exceptional coercivity

Sub-50 nm particle sizes dramatically increase coercivity due to domain-wall pinning.

Where Science Meets Supply Chains: The China Question

Although the review is not geopolitical, the backdrop is impossible to ignore: China performs roughly 90% of all rare earth magnet processing worldwide. Even if MnBi reduces rare-earth dependency at the magnet stage, global EVs, turbines, and motors still overwhelmingly rely on NdFeB magnets.

MnBi may help diversify applications—but only if its own manufacturing bottlenecks can be overcome.

Limitations and Challenges: The Hard Truth Behind the Hype

1. Phase-stability problems

LTP-MnBi is metastable, easily shifting into inferior phases with small temperature or compositional deviations.

2. Manufacturing complexity

Producing high-purity MnBi requires tight control over:

• Thermal windows
• Stoichiometry
• Oxidation prevention
• Avoidance of eutectic melting

Scaling these conditions to multi-ton production is notyet feasible.

3. Moderate magnet strength

Even in the most optimistic scenarios, MnBi’s (BH)max maxes out around 20–25 MGOe, well below China’s sintered NdFeB.

4. Thin films and nanoparticles remain lab-only

The strongest results come from microscopic samples—not bulk magnets suitable for motors or industrial deployment.

Implications for Investors and Policymakers

This review should be read as a scientific roadmap, not a commercialization announcement. Still:

• MnBi could emerge as a supplementary magnet class, especially at high temperatures where NdFeB loses strength.
• MnBi may reduce rare-earth intensity in selected applications.
• Exchange-coupled MnBi composites are the closest to bridging the performance gap.

But the core bottleneck remains unchanged: the West cannot reduce dependency on China without building midstream refining and magnet-making capacity.MnBi does not eliminate that structural problem.

Conclusion

Mallik and Srivastava deliver one of the clearest, most authoritative MnBi reviews to date—showing that the material is far more technically advanced than many assume. Its coercivity, thermal resilience, and promising exchange-coupling behavior make MnBi a serious contender among rare-earth-free magnet materials.

But the gap between laboratory breakthroughs and market-ready magnets is still wide. Stabilizing the MnBi phase, scaling its production, and engineering bulk forms all remain significant obstacles. And even with progress, the global magnet industry will continue to revolve around NdFeB—unless Western nations accelerate investment in processingtechnologies currently monopolized by China.

 Citation: Mallik, B. & Srivastava, S.K. (2026). Recent development on magnetic properties of MnBi alloys (opens in a new tab). Next Materials, 10, 101501.

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