PdMn and PdFe: New materials for temperature measurement near 2 K

Interest in the critical dynamics of superfluid He-4 in microgravity conditions has motivated the development of new high resolution thermometry technology for use in space experiments near 2 K. We have developed a magnetic thermometer using dilute magnetic alloys of Mn or Fe dissolved in a pure Pd matrix, similar to previous thermometers used at ultra-low temperatures. These metallic thermometers are easy to fabricate, chemically inert, and can have a low thermal resistance to the stage to be measured Also, the Curie temperature can be varied by changing the concentration of Fe of Mn, making them available for use in a wide temperature range. The derivative of the magnetic susceptibility was measured for PdMn and PdFe between 1.5 K and 4 K using a SQUID magnetometer. These measurements, as well as preliminary noise and drift measurements, show them to have sub-nK resolution with a drift of less than 10(-13) K/s.