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Physical Measurements Service
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He-3 option
  • Acquired on February 2005.
  • Opción He-3
  • The helium-3 refrigerator cools down to 0.35 K by pumping on a bath of liquid 3He. It is compatible with the PPMS options resistivity, AC electric transport and heat capacity. Basically, it is a closed 3He circuit whose flux is controlled by a set of valves, a diaphragm pump, and a turbo pump. The cold finger (pot) is in contact with the platform where the sample holders are installed. The probe is inserted in the PPMS chamber.
  • Temperature range: 350 mK a 350 K.
  • Magnetic field range: 0 a ± 9 T, ± 14 T.
  • Sample holders:
    • They are specific for the He-3 option.
    • They can be installed either parallel or perpendicular to the applied magnetic field.
  • Temperature operating modes:
    • 350 K – 4 K.
      Both cooling and heating are provided through the PPMS sample chamber with feedback from the thermometer located on the Helium-3 sample platform. *
    • 4 – 2.5 K.
      The PPMS sample chamber is maintained below 2 K and the heater located on the Helium-3 sample stage is used to raise the temperature up to the set point. The 3He is pumped away from the cold end of the probe to avoid condensing 3He in the pot.
    • 2.5 – 0.5 K.
      The PPMS sample chamber is maintained below 2 K. Cooling is provided by circulating 3He. The turbo pump speed is adjusted depending on the temperature set point and the heat load. At temperatures below about 1 K, liquid 3He collects in the pot.
    • 0.5 - 0.35 K.
      The PPMS sample chamber is maintained below 2 K. To achieve T < 0.45 K, not possible in the circulating state, the system operates in a one-shot mode where the supply of 3He to the impedance is cut off. Without the warm liquid flowing into the pot, the system can attain temperatures below 0.4 K. Operation in one-shot mode is limited to about 90 minutes before the pot must be refilled, as the pot is not refilled continuously.
      El "pot" tiene una autonomía aproximada de 1 h.
  • Resistivity measurements:
    • For highly resistive samples a large excitation current may produce a heating of the sample, noticeable at T < 1 K.
  • Heat capacity measurements:
    • The wires supporting the sample platform of the He-3 heat capacity puck are thinner than the ones of the standard puck so that sample mounting should be performed carefully. Also, in magnetic samples, the magnetic field may torque sample platform and break the wires.
* at T=20 K high vacuum is initiated to avoid condensing helium at the bottom of the probe.