Development and application of rare earth intermetallic compounds to working substances for extremely low-temperature refrigerator of small size

1 Magnetic susceptibilities are measured for the rare earth intermetallic compounds of ErAg，HoAu_2，ErAu_2and Er_2Au.As for the compounds of HoAu_2and Er_2Au，it is found that temperature dependence of the susceptibilities make anomalies other than those found previously。These anomalies suggest the existence of new magnetic order-order transitions in these compounds.2 Specific heats of these compounds except for Er_2Au are measured between2and30K.ErAg：Mother anomaly is found at a temperature just below the Noel temperature(T_N)，where the suscibeptility anomaly is not observed.The peak value of specific heat is obtained to be about20J·K^&lt；-1&gt；·mol^&lt；-3&gt；(0.7J·K^&lt；-1&gt；·cm^&lt；-3&gt；)at T_N.HoAu_2：A peak in the specific heat is observed at the temperature where the new anomaly is found in susceptibility mentioned above.The specific heat at T_N has a peak value of 10J·K^&lt；-1&gt；·mol^&lt；-3&gt；(0.27J·K^&lt；-1&gt；·cm^&lt；-3&gt；)。ErAu_2：The maximum value of specific heat T_N is13J·K^&lt；-1&gt；·mol^…More&lt；-3&gt；(0.36J·K^&lt；-1&gt；·cm^&lt；-3&gt；)。Er_2Au：A jump of specific heat per unit volume at T_Nis roughly estimated to be about1.5 times of that of ErAg on the basis of molecular field approximation.3 The specific heats of ErAg，HoAu_2and ErAu_2per unit volume below10K are found to be lower than that of He gas which is used as a working substance of low-temperature refrigerator，It is found that the specific heats per unit volume of the compounds at per unit volume of the compounds at temperature substance of low-temperature refrigerator of the that that the specific heats per unit volume of the compounds at temperature substance of the themperature refrigerator of the temperature refrigerator of the that that the specific heats per unit volume of the compounds at per unit volume of the temperature refrigerator of the that that the specific heats per unit volume at at to thecific heat at temperatures below a a herthan at herthat of the thecific heats per unit volume temerator of the temerator of the temtemperature refrigerator，that that the specific heat temit volume tunit volume s.Therefore，it may be probable to make a regenerator from composite materials of these compounds and lead，so as to discharge heat of He gas below10K mainly to these compounds and above10K mainly to lead.As for the compound Er_2Au，a jump of specific heat per unit volume，which is estimated to be more than a half of the peak value of the specific heat of He gas at about8K，is expected around the same temperature range(T_N=6.2K)。Less：Less

1 Magnetic susceptibilities are measured for the rare earth intermetallic compounds of ErAg, HoAu_2, ErAu_2 and Er_2Au. As for the compounds of HoAu_2 and Er_2Au, it is found that temperature dependence of the susceptibilities make anomalies other than those found previously. These anomalies suggest the existence of new magnetic order-order transitions in these compounds.2 Specific heats of these compounds except for Er_2Au are measured between 2 and 30 K.ErAg : Mother anomaly is found at a temperature just below the Noel temperature (T_N), where the susceptibility anomaly is not observed. The peak value of specific heat is obtained to be about 20 J・K^<-1>・mol^<-3> (0.7 J・K^<-1>・cm^<-3>) at T_N. HoAu_2 : A peak in the specific heat is observed at the temperature where the new anomaly is found in susceptibility mentioned above. The specific heat at T_N has a peak value of 10 J・K^<-1>・mol^<-3> (0.27 J・K^<-1>・cm^<-3>). ErAu_2 : The maximum value of specific heat at T_N is 13 J・K^<-1>・mol^ … More <-3> (0.36 J・K^<-1>・cm^<-3>). Er_2Au : A jump of specific heat per unit volume at T_N is roughly estimated to be about 1.5 times of that of ErAg on the basis of molecular field approximation.3 The specific heats of ErAg, HoAu_2 and ErAu_2 per unit volume below 10 K are found to be lower than that of He gas which is used as a working substance of low-temperature refrigerator, It is found that the specific heats per unit volume of the compounds at temperatures below 10 K are higher than that of lead used generally for a regenerator (below 17 K in the case of ErAg). Therefore, it may be probable to make a regenerator from composite materials of these compounds and lead, so as to discharge heat of He gas below 10 K mainly to these compounds and above 10 K mainly to lead. As for the compound Er_2Au, a jump of specific heat per unit volume, which is estimated to be more than a half of the peak value of the specific heat of He gas at about 8 K, is expected around the same temperature range (T_N=6.2 K). Less