A Record-High Cryogenic Magnetocaloric Effect Discovered in EuCl₂ Compound.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Thermodynamics

Background:

• Adiabatic demagnetization refrigeration (ADR) utilizes the magnetocaloric effect (MCE) for cryogenic applications.
• Existing magnetic refrigerants show magnetic entropy change (ΔSM) significantly below theoretical maximums.
• Optimizing MCE is crucial for advancing ADR technology.

Purpose of the Study:

• To investigate the magnetocaloric properties of orthorhombic EuCl2.
• To explore EuCl2 as a potential high-performance cryogenic refrigerant.
• To achieve a magnetic entropy change approaching theoretical limits.

Main Methods:

• Combined ab initio calculations with Brillouin function analysis.
• Conducted magnetic measurements to determine magnetic properties.
• Performed direct quasi-adiabatic demagnetization experiments.

Main Results:

• Demonstrated a ferromagnetic ground state in EuCl2 with excellent single-ion behavior.
• Achieved a record-high magnetic entropy change (ΔSM) of ~74.6 J·kg−1·K−1 at 1.8 K and 5 T, reaching 96% of the theoretical limit.
• Recorded the highest-ever ΔSM of ~36.8 J·kg−1·K−1 at 1 T and maintained sub-Kelvin temperatures (~346 mK) for an extended duration.

Conclusions:

• Orthorhombic EuCl2 exhibits giant magnetocaloric effect surpassing existing materials.
• EuCl2's performance positions it as a highly attractive material for cryogenic refrigeration.
• The material's ability to maintain sub-Kelvin temperatures offers significant advantages for ADR.