The construction and performance of a single stage nuclear demagnetization apparatus utilizing 0.267 mole of praseodymium nickel material is described. An optimization procedure to minimize entropy production during the demagnetization of the hyperfine enhanced material has been developed which enabled the cryostat to cool a liquid‐3He sample to a temperature of 350 μK. The effects of measured heat leaks and inferred eddy‐current heating are accounted for satisfactorily in a model of this procedure.
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