The material system
A central focus of my work is La(Fe,Si)₁₃-based alloys — recognized for their giant magnetocaloric effect, high magnetization, and low cost, which makes them strong candidates for real magnetic refrigeration devices.
The scientific challenge is twofold: tuning the Curie temperature up from the pure compound's ~200 K to near room temperature, and taming the thermal hysteresis that comes with the alloy's first-order phase transition. I've approached both problems through systematic chemical substitution — Mn, Co, Ni, and Cr — and through hydrogenation of the material.
Why it matters beyond the lab
Liquid hydrogen is central to a carbon-neutral energy system, but making it is inefficient. Conventional Joule-Thomson expansion liquefaction runs at only about 23% efficiency — too costly for large-scale use.
Magnetocaloric liquefaction changes that math: theoretical models put its efficiency above 60%, which is what makes affordable liquid hydrogen production plausible at scale. The catch is materials — this needs alloys with large magnetic entropy and adiabatic temperature change across the 77 K (nitrogen) to 20 K (hydrogen) range, under magnetic fields that are practical to generate commercially.
The materials dilemma
Materials selection for magnetocaloric hydrogen liquefaction runs into a hard trade-off between performance and resource criticality.
⬤ High performance
Heavy rare-earth intermetallics deliver superior magnetocaloric performance — but these elements are highly critical in terms of resource availability.
◯ High availability
Light rare earths are relatively abundant and far less critical — but their alloys generally show weaker magnetocaloric properties.
This performance-versus-criticality trade-off is central to scaling magnetocaloric technology for widespread adoption — and it's the throughline across the contributions below.
Key contributions
Faster, better sample processing
Combining induction melting with suction casting shortened the annealing time of La(Fe,Si)₁₃ compounds by an order of magnitude — improving processing efficiency and widening the range of obtainable NaZn₁₃-type structures. This became the foundation for the systematic substitution studies that followed.
Ni substitution: tuning the transition order
Ni addition raises the transition temperature and, more importantly, converts the phase transition from first-order to second-order. DFT calculations showed Ni atoms preferentially occupy 96i sites without materially changing the total magnetic moment — giving a theoretical basis for the experimental result.
Cr substitution: a counterintuitive result
La(Fe,Cr,Si)₁₃ compounds retain both the magnetocaloric response and the first-order character of the transition despite a significant drop in magnetic moment — challenging the assumption that magnetocaloric performance and moment size must track together.
Mn doping: atomic-scale structure
Using XMCD, EXAFS, and DFT together, this work resolved how Mn doping reshapes the local magnetic and geometric structure of La(Fe,Si)₁₃ — atomic-scale insight into a macroscopic property.
A sharper criterion for transition order
Co-developed a quantitative criterion for classifying magnetic phase transition order from the magnetocaloric effect itself — more accurate than the conventional Banerjee criterion, especially for compositions sitting near the critical point where the transition order is ambiguous.
Mastering hysteresis
Co-authored a comprehensive review on reducing thermal and magnetic hysteresis in first-order magnetocaloric materials — one of the main obstacles between lab-grade material and a device that can cycle reliably.
Composites that survive a real device
Most room-temperature magnetocaloric materials are brittle and corrosion-prone — hard to put directly into a cooling machine. I developed polymer-bonded and metal-bonded composites of La(Fe,Mn,Si)₁₃Hₓ for active magnetic regenerators, systematically mapping how powder particle size, adhesive type and concentration, and compaction pressure affect performance — and introduced a low-melting Field's-metal binder to solve the fatigue issues polymer binders suffer from the material's large magnetovolume effect.
Multi-property probing of the transition
Contributed to simultaneous multi-property probing techniques that combine element-specific and macroscopic hysteresis characterization during magneto-structural phase transitions — giving a more complete picture of what happens inside the material as it switches.
Beyond magnetic field: pressure and multicaloric effects
Ongoing work on the pressure dependence of the MCE and on multicaloric effects — stimulating the material with more than one field at once. In FeRh, exploiting thermal hysteresis across multi-stimuli cycles that combine pulsed magnetic fields with uniaxial load points toward devices that need a smaller, cheaper magnetic field to do the same job.
The supply-chain stakes
This isn't only a materials-science problem — it sits inside a real geopolitical bottleneck.
China's share of NdFeB production
China controls this share of global NdFeB magnet production and dominates midstream rare-earth separation and metal conversion — a critical choke point for Europe and North America.
Rare earth magnet market by 2028
Projected market size, driven by the accelerating shift to electric vehicles, wind power, and other clean-energy technologies.
In response, the European wind industry — with the German Federal Ministry for Economic Affairs and Energy — has set a resilience roadmap targeting 30% of permanent magnets from alternative sources by 2030, rising to 50% by 2035. Research that reduces reliance on critical heavy rare earths, or reduces the field strength a device needs in the first place, feeds directly into that roadmap.