New application of complex magnetic materials to the magnetic refrigerant in an Ericsson magnetic refrigerator

TLDR

Ferromagnets are required as magnetic refrigerants above ~15 K, yet homogeneous ferromagnets exhibit temperature‑dependent entropy changes that are unsuitable for the Ericsson cycle. The study verifies theoretically that a complex ferromagnetic alloy such as (ErAl₂)₀.₃₁₂(HoAl₂)₀.₁₉₈(Ho₀.₅Dy₀.₅Al₂)₀.₄₉₀ possesses the optimal properties for an ideal Ericsson cycle, including two isomagnetic field processes. The authors fabricated a sintered multilayer complex of three RAl₂.₁₅ rare‑earth layers and measured its specific heat to determine entropy and entropy change. The complex magnetic material was found to be a promising refrigerant for the Ericsson cycle, demonstrating suitable entropy change characteristics.

Abstract

A complex new magnetic refrigerant, suitable for the ideal Ericsson cycle, has been investigated. Above ∼15 K it is necessary to use ferromagnets as a magnetic refrigerant. However, temperature variation for the magnetic entropy change in a homogeneous ferromagnet is not suitable for the Ericsson cycle. The present paper verifies, from theoretical analysis, that a complex ferromagnetic material, for instance, (ErAl2)0.312(HoAl2)0.198 (Ho0.5Dy0.5Al2)0.490, has the most suitable characteristics for the ideal Ericsson cycle, including two kinds of isomagnetic field processes. On the basis of the above consideration, a sintered layer structural complex has been prepared, composed of three kinds of RAl2.15 layers, where R’s are rare-earth atoms. From specific heat measurements made on this complex, its entropy and entropy change have been determined. It has been concluded that the complex magnetic material is the most hopeful refrigerant for the Ericsson cycle.