MicroKelvin research facility: double-stage nuclear demagnetization cryostat

The cryostat consists of a dilution refrigerator and a double-stage nuclear demagnetization unit of PrNi₅ (0.9 moles) and 0.2 moles of copper in series. This cryostat has reached 30 µK in the copper nuclear spin system. The first stage is limited to T > 400 µK because the Praseodymium nuclear spins order at this temperature, but due to its large heat capacity it can stay below 1 mK for 2 weeks.

The figure shows the dilution unit built in the WMI and the first nuclear demagnetization stage along with the recently used pressure cell for NMR on solid 3He. The upper part of this is a capacitive strain gauge to measure the pressure in the cell, the lower part has Helmholtz gradient coils on top of the NMR pickup coils.	The above image shows the second demagnetization stage of 0.2 moles of copper with NMR samples to study nuclear spin dynamics and to measure the temperature. Lowest temperature reached: 30 µK for the nuclear spins.

In our cryostat three measuring platforms contain a calorimeter, a capacitive torque magnetometer, both in fields up to 8 T, and a SQUID magnetometer to determine the static magnetic susceptibility of small samples. In addition, we employ a pulsed and continuous wave nuclear magnetic resonance spectrometer to mesure temperatures below 10 mK and to study nuclear spin dynamics.

 

Research with this facility includes:

• NMR on solid ³He
• Heat capacity measurements on Heavy Fermion systems
• Transport measurements on 2-dimensional electron gases

For details see our ULT home page