New low-criticality family of alloys sets benchmark for sustainable magnetic refrigeration

The research group Functional Materials for Sustainability and Resilience (FunMat4SuRe) at University of Seville (Spain) has demonstrated the efficacy of a new "criticality-aware design strategy," creating a MnNiSi-containing high-entropy alloy (HEA) system optimized for magnetic refrigeration. By utilizing co-substitution of iron and copper, the structural transition temperature of the starting material is effectively reduced by more than 900 K, enabling a first-order magnetostructural transformation to occur near room temperature. Magnetostructural coupling remarkably enhances the magnetocaloric response of the alloys, surpassing previous records for cobalt (Co)-, germanium (Ge)-free magnetocaloric HEAs by 360%. This study establishes a solid framework for designing low-criticality high entropy alloys employed in magnetic refrigeration technologies.

As rising global temperatures drive a surge in energy demand for air conditioning, the need for eco-friendly alternatives to traditional vapor-compression refrigeration systems is imperative. Magnetic refrigeration, based on the magnetocaloric effect (MCE), is a leading candidate, but it has historically faced a difficult trade-off: high performance usually relies on "critical raw materials" like rare earths, cobalt, or germanium, which are costly and vulnerable to supply chain disruptions.

To address this, the research group focused on third-generation HEAs, specifically the MnNiSi system, to engineer a material that is both abundant and highly effective.

Key Technical Achievements:

• Beyond Critical Elements: The design successfully bypasses the need for cobalt, germanium, and rare earth elements.
• Drastic Temperature Control: The Mn_0.5Fe_0.5Ni_1-xCu_xSi compositional series reduces the structural transition temperature by over 900 K relative to the base material, bringing it to the desired temperature range.
• Room Temperature Viability: The material successfully tunes for a first-order magnetostructural transformation over a broad temperature range of 100 K, which includes room temperature, making it viable for practical applications.
• Record-Breaking Efficiency: The material exhibits the highest magnetocaloric effect ever reported for a HEA free of critical elements (including Co, Ge), outperforming previous records by 360%. This magnetocaloric performance is also highly competitive compared with Co-, Ge-, RE-containing HEAs and is surpassed by only a few of the critical-element-containing ones, which display working temperatures significantly below RT.

Complementary density functional theory calculations confirmed the stability of the material, and predictions of lattice entropy closely match experimental measurements. This research establishes that high-performance cooling does not require high environmental costs, offering a scalable framework for the future of resource-resilient technology.

About the Functional Materials for Sustainability and Resilience (FunMat4SuRe) Group

FunMat4SuRe, located at University of Seville, Spain, is at the forefront of magnetic high-entropy alloys research.

Led by Prof. Victorino Franco, the activities of the group span over a broad spectrum of areas of interest:  discovering new advanced magnetic materials for energy applications, developing novel instrumentation and analysis techniques, and designing functional materials for additive manufacturing. This is achieved by a combination of experimentation and simulation that blends first principles and machine learning tools. The current work lies on one of the main aims of the group:  addressing global sustainability challenges through the development of novel, resource-efficient functional HEAs and magnetocaloric systems.

Reference: Elisa Guisado-Arenas, Zhe Cui, Luis M. Moreno-Ramírez, Carlos Romero-Muñiz, Jia Yan Law, Victorino Franco. A criticality-aware design framework for sustainable magnetocaloric high-entropy alloys: the MnFeNiCuSi system[J]. Materials Futures. DOI: 10.1088/2752-5724/ae36c5