High-efficiency magnetic refrigeration using holmium.

Area of Science:

• Thermodynamics
• Materials Science
• Cryogenics

Background:

• Magnetic refrigeration (MR) is a cooling technology utilizing magnetic fields.
• Current MR research targets low temperatures (20 K) for hydrogen liquefaction.
• High magnetic fields (≥5 T) and superconducting magnets are typically required, leading to high energy costs.

Purpose of the Study:

• To propose a highly efficient and energy-saving cooling technique for magnetic refrigeration.
• To achieve significant cooling efficiency with low magnetic field changes.
• To develop a viable alternative for hydrogen liquefaction cooling.

Main Methods:

• Utilizing holmium, a material with steep magnetization changes.
• Employing small magnetic field variations (Δμ₀H ≤ 0.4 T).
• Implementing the technique with permanent magnets.

Main Results:

• Achieved a cooling efficiency of -ΔS_M/Δμ₀H = 32 J kg^-1K^-1T^-1.
• Demonstrated one order of magnitude higher efficiency than typical magnetocaloric materials.
• Showcased the potential for efficient cooling with low magnetic fields.

Conclusions:

• The proposed method offers a highly efficient magnetic refrigeration technique.
• The use of holmium and permanent magnets reduces energy requirements.
• This approach presents a promising alternative to conventional gas compression cooling for hydrogen liquefaction.