Highlights

• University of Florence PhD demonstrates strontium hexaferrite can be engineered into improved 'gap magnets' that outperform conventional ferrites while avoiding rare earth supply chain risks.
• Research achieved high coercivity (up to 0.7 T) and density (92-97%) through nanoparticle synthesis, Al/Mn doping, and advanced pressing techniques, though performance trade-offs remain.
• Recycled ferrite magnets showed commercial-grade properties, offering a practical circular-economy pathway to partially substitute rare earth magnets in moderate-performance motors and components.

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A new PhD thesis by Alessandro Gerace (opens in a new tab), completed at the University of Florence (PhD in Chemical Sciences), investigates whether hexagonal ferrites—particularly strontium hexaferrite (SrFe₁₂O₁₉, or SrM)—can be engineered into higher-performance permanent magnets capable of partially substituting rare-earth-based magnets in applications that do not require the very highest magnetic strength.

Rather than attempting to replace neodymium-iron-boron (NdFeB) magnets outright, the research focuses on developing so-called “gap magnets”: materials that outperform conventional ferrites while remaining cheaper, more abundant, and less exposed to rare earth supply-chain risk.

The motivation is both technical and strategic. Rare-earth magnets underpin electric vehicles, wind turbines, and advanced electronics, but their supply chains—especially processing and magnet manufacturing—are highly concentrated. Gerace’s work asks a pragmatic question: can improved ferrites take over part of the magnet market, reserving rare-earth magnets only for applications where their performance is truly indispensable?

How the Research Was Conducted

The thesis is firmly rooted in materials science and magnet engineering, not policy modeling. Gerace develops and tests a multi-step approach to improving ferrite performance:

• Synthesis: Scalable preparation of phase-pure SrM nanoparticles using low-temperature solid-state and modified sol-gel routes.
• Doping: Substitution of iron sites with non-rare-earth dopants, particularly aluminum and manganese, to tune coercivity and particle size.
• Densification and alignment: Formation of dense magnets using multi-anvil pressing, piston-cylinder pressing, and spark plasma sintering (SPS).
• Composite exploration: Experimental hard–soft systems combining SrM with iron nanowires to probe magnetic interactions.
• Industrial validation: Assessment of recycled ferrite materials for bonded magnets in collaboration with industry.

Throughout, the thesis emphasizes industrial relevance—how materials behave not only in the lab, but when pressed, aligned, and processed at scale

Key Findings

1. Improved ferrites are technically achievable.

The research demonstrates that ferrite properties can be meaningfully tuned through nanoparticle size control, chemical substitution, and alignment during compaction.

2. Doping boosts resistance to demagnetization—but trade-offs emerge.

Al- and Mn-doped SrM powders achieved high coercivity values (reported up to ~0.7 T in powder form) and very small particle sizes (around ~40 nm for Mn-doped samples). However, coercivity often declined after densification—a known effect when magnetic grains interact more strongly in bulk magnets.

3. Very high densities are possible, with consequences.

Using advanced pressing and SPS, relative densities as high as ~92–97% were reported for selected samples. Higher density improved remanence and alignment but tended to reduce coercivity, illustrating the classic performance trade-off in permanent magnet engineering.

4. Recycled ferrites show near-term promise.

One of the most practical outcomes is the demonstration that bonded magnets made from recycled ferrite production waste can achieve magnetic properties comparable to commercial ferrite grades, supporting ferrites as a realistic circular-economy material.

Why This Matters for the Rare Earth Magnet Supply Chain

The thesis cites external industry outlooks showing that rare earth processing and magnet manufacturing are far more concentrated than mining, with China holding a dominant position. While this dominance is not Gerace’s original dataset, it provides essential context.

If “gap magnets” can displace even a portion of rare-earth magnet demand—particularly in moderate-performance motors and components—the result would be reduced pressure on rare-earth processing bottlenecks and greater flexibility for Western manufacturers.

Limitations and Open Questions

Gerace does not claim ferrites can replace NdFeB magnets in high-power, space-constrained applications.

Key limitations include:

• Performance ceiling: Even optimized ferrites remain below rare-earth magnets in maximum energy product.
• Manufacturing complexity: Preserving coercivity while achieving high density and alignment remains challenging.
• Scale-up realism: Some synthesis routes are difficult to scale; industrial trials relied on commercial and recycled powders for volume reasons.
• Composite uncertainty: Hard–soft nanocomposites did not demonstrate clear exchange coupling under the tested conditions.

Conclusion

This thesis does not promise a rare-earth-free future—but it makes a strong case for strategic substitution. By improving ferrites where performance requirements allow, rare-earth magnets can be reserved for applications that truly need them. In a world of tightening supply chains and rising electrification demand, that distinction matters.

Citation: Gerace, A. Improving the Properties of Hexagonal Ferrites for the Replacement of Rare Earth Permanent Magnets (opens in a new tab). PhD Thesis, University of Florence.

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