We investigated the Ericsson type magnetic refrigerators in the range below 77 K. This is the first report of experimental results of the refrigeration character, especially the magnetocaloric character of RAl//2, where R is a rare earth atom. The specific heat and magnetization were measured precisely as a function of temperature and magnetic field. From analyses of these results the total entropies S and the magnetic entropy changes DELTA S//J of the RAl//2 series were determined. It is made clear that a large enough value of DELTA S//J to make refrigeration can be induced by the external magnetic field near T//c, and also that the temperature corresponding to the maximum value of DELTA S//J is adjustable by making a solid solution between the compounds in the RAl//2 series. It is therefore concluded that the RAl//2 series is a promising candidate for refrigerant at above 20 K.