The future of eco-friendly cooling: Enhancing efficiency and sustainability of magnetic refrigerants

Conventional air conditioners and refrigerators rely on vapor-compression cycles and chemical refrigerants that contribute significantly to global warming. Magnetic refrigeration offers a cleaner alternative using the magnetocaloric effect (MCE), a phenomenon where certain materials change temperature when exposed to a magnetic field. Until now, researchers have faced a fundamental dilemma: Materials with a high cooling effect often suffered from irreversible energy losses, an effect known as hysteresis, which leads to rapid degradation in the cooling effect under operating conditions. Conversely, the conventional durable materials failed to achieve the large cooling effect required for practical application.

Researchers from a global consortium, including NIMS (Japan), TU Darmstadt (Germany), and other institutes, have now unlocked a new pathway toward sustainable refrigeration. Published in Advanced Materials, the study highlights a significant leap forward in cooling technology.

The research team achieved a decisive breakthrough using a novel approach to material design. By fine-tuning atomic bonding (covalent bonding) through precise control of the chemical composition, they were able to minimize irreversible energy losses. The study focused on a compound of gadolinium (Gd) and germanium (Ge). This magnetic cooling material, Gd₅Ge₄, heats up when an external magnetic field makes the atoms' tiny magnetic "spins" line up.

The researchers identified that the performance degradation of this material is caused by a structural transition that occurs during magnetic transitions. In Gd₅Ge₄, changing bond lengths between Germanium atoms, which connect the structural slabs, contribute to hysteresis and performance degradation during repeated cycling.

To solve this, the team replaced a portion of the germanium with tin (Sn) atoms to precisely tune the material's covalent bonding. This chemical adjustment stabilizes the distance between the material's internal structural slabs during transitions, effectively "cushioning" the atomic displacement that previously led to degradation.

Results and future impact

The impact of this tuning is profound. The material now maintains its cooling over repeated cycles while simultaneously more than doubling its reversible adiabatic temperature change (the temperature change without external heat exchange) which rose from 3.8°C to 8°C.

This breakthrough enhances both the magnetocaloric effect and the material's overall durability, paving a sustainable, high-performance path for magnetic refrigerants. Because these materials operate efficiently at cryogenic temperatures, ranging from approximately -233°C to -113°C, they are an ideal choice for gas (including hydrogen, nitrogen, and natural gas) liquefaction. As a result, they represent a key component in the development of eco-friendly gas liquefaction technologies.

Looking ahead, the consortium plans to apply this methodology to a broader range of compounds, expanding the technology's reach across various cooling and gas liquefaction sectors.