Self-balancing, calibrated CMN thermometer with digital readout

Publisher Website
Google Scholar
Abstract
We have developed a modification of the SQUID–CMN thermometer of Giffard, Webb, and Wheatley which has the advantages of (1) not needing recalibration against a thermometric standard at the beginning of each run, and (2) its accuracy not depending upon the absence of mechanical or electrical transients. A special current source provides a smoothly adjustable current to a field‐generating solenoid around the CMN. The SQUID output can either be measured directly with a digital voltmeter for high accuracy, or it can be fed to an analog dividing circuit which converts it to temperature with 1/2% accuracy and displays it directly in mK. The thermometer apparatus is not restricted to measurements of CMN; 1 mm3 samples of other materials can easily be measured in fields of a few oersteds. The absolute uncertainty in χ is 10−5 emu/cm3, while relative changes of 2×10−7 emu/cm3 or smaller can be detected. We have observed marked deviations from a Curie law in partially dehydrated CMN below ∼0.2 K. This illustrates the danger of pumping a vacuum on CMN powder at room temperature.
Keywords