Improved Demagnetization Cryostat for Mössbauer Effect Experiments

Some improvements in a previously constructed demagnetization cryostat for use in Mössbauer effect experiments have been made. In the new design, a mechanical heat switch previously used for establishing thermal contact between the paramagnetic salt and the liquid helium bath was replaced with helium exchange gas; the use of vacuum-tight beryllium windows has made it possible. CrK alum or MnNH 4 Tutton salt weighing 60 g was used as a cooling salt. The lowest temperature reached by using CrK alum was 0.025°K and temperature of the alum arrived at 0.05°K in 6.5 hr. The lowest temperature reached by using MnNH 4 Tutton salt was 0.15°K and temperature of it was practically constant as long as liquid helium stayed in the bath. The magnetic hyperfine structure of K 3 Fe(CN) 6 ( T N =0.13°K) has been observed by employing this cryostat, and the internal magnetic field at the position of an iron nucleus in K 3 Fe(CN) 6 was found to be 193 kOe.