Publications Details
PdMn and PdFe: New Materials for Temperature Measurement Near 2K
Interest in the critical dynamics of superfluid 4 He in microgravity conditions has motivated the development of new high resolution thermometry technol- ogy for use in space experiments near 2K. The current material commonly used as the temperature sensing element for high resolution thermometers (HRTs) is copper ammonium bromide [Cu(NH4)2Br42H20) or "CAB", which undergoes a ferromagnetic phase transition at 1.8K1. HRTs made from CAB have demonstrated low drift (< 10fK/s) and a temperature resolu- tion of O.lnK. Unfortunately, paramagnetic salts such as CAB are difficult to prepare and handle, corrosive to most metals, and become dehydrated if kept, under vacuum conditions at room temperature. We have developed a magnetic thermometer using dilute magnetic alloys of Mn or Fe dissolved in a pure Pd matrix. These metallic thermometers are easy to fabricate, chemically inert, and mechanically robust. Unlike salts, they may be directly soldered to the stage to be measured. Also, the Curie temperature can be varied by changing the concentration of Fe or Mn, making them available for use in a wide temperature range. Susceptibility measurements, as well as preliminary noise and drifl measurements, show them, to have sub-nK resolution, with a drift of less than 10-13 K/s.