A complex type of magnetic refrigerant for the Ericsson cycle has been investigated. For the magnetic refrigerant in the temperature range above -15K we have to use the ferromagnetic material, which has the internal magnetic field to arrange its spin system as far as using a magnetic field of -6T, because of increasing of the thermal excitation energy for spins -kT. Moreover, we have to select the Ericsson cycle instead of the Carnot cycle usually used in the low temperature range below -15K, since the lattice entropy of a solid material in this range is not negligible in comparison with the magnetic entropy.
In order to form a high efficient Ericsson cycle that includes two kinds of iso-magnetic field processes, a new severe condition is required for the magnetic refrigerant, that is, the magnetic entropy change ΔSJ is constant in the refrigeration range. This condition, however, can not be satisfied by an usual homogeneous ferromagnetic substance.
In the present paper we first made clear from the theoretical analysis that the complex of the ferromagnetic materials, for instance (ErAl2)0.312(HoAl2)0.198(Ho0.5Dy0.5Al2)0.490, well satisfies the above condition.
On the basis of the analysis we have prepared a complex consisted of several RAl2.15 compound layers with different rare earths R, such as (ErAl2.15)0.312(HoAl2.15)0.198(Ho0.5Dy0.5Al2.15)0.490. For the complex we determine the magnetic entropy change ΔSJs and the entropy S from the specific heat measurement.
From these results we can conclude that the layer type complex material is most hopeful not only for the Ericsson type magnetic refrigerant but also for the regenerative material.
