[en] 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)/sub 0.312/(HoAl₂)/sub 0.198/ (Ho/sub 0.5/Dy/sub 0.5/Al₂)/sub 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 RAl/sub 2.15/ 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