Researchers boost viability of magnetic refrigeration

GERMANY: Researchers from Germany and Japan claim to have unlocked a way to enhance the performance of magnetocaloric refrigeration and improve the material’s durability. 

The magnetocaloric effect, a phenomenon where certain materials change temperature when exposed to a magnetic field, could potentially pave the way for a more sustainable alternative to vapour compression technology.

Until now, researchers have faced a fundamental dilemma: materials with a high cooling effect often suffer from irreversible energy losses, an effect known as hysteresis, which leads to rapid degradation in cooling effect under operating conditions. Conversely, the conventional durable materials fail to achieve the large cooling effect required for practical application.

The research team, comprising representatives from Germany’s Technical University of Darmstadt and the National Institute for Materials Science (NIMS) in Japan, along with other prestigious institutes, claim to have 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 minimise 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.

As a result of these changes, the material is said to maintain its cooling over repeated cycles while simultaneously more than doubling its reversible adiabatic temperature change, 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 seen as an ideal choice for gas liquefaction. 

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

The other contributors to this international research included the Kyoto Institute of Technology (KIT) in Japan, the Japan Synchrotron Radiation Research Institute (JASRI), and the University of Hyogo and Tohoku University in Japan.