Basic researches for development of regenerator materials having giant magnetic specific heats and high thermal conductivitie

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Main conclusions derived from the present research project are summarized below.(1) The low temperature specific heat and magnetic properties have been studies on various rare earth-Ag alloys whose magnetic transition temperature falls in the range 3-40K.We found that Er-Ag, 2r-Ag-Al, Er-Ag-Ga, Pr-Ag, Nd-Ag, Pr-Nd-Ag alloys possess both extremely large magnetic specific heat and high thermal conductivities in the relevant temperature range and that they are well suited as the regenerator materials.(2) We could successfully prepare the Er-Ag spherical particles with 0.1-0.2mm in diameter. We could reach the lowest temperature of 7K by using the Er-Ag particles as regenerator materials in the conventional GM refrigerator.(3) We modified the onventional GM refrigerator and could monitor the pressure and temperature during cooling and heating stages at various positions in the regenerator materials by mounting pressure and temperature sensors. In this way, we could establish the system to evaluate the regenerator materials suitable for the refrigerator.