Low Temperature Thermometry in High Magnetic Fields. I. Carbon Resistors

Measurements of the transverse (sample current I normal to magnetic field H) and longitudinal (I∥H) magnetoresistance of 110, ⅛, and ¼ W Allen-Bradley carbon resistors were performed at various temperatures between 1.8 and 18 K in static magnetic fields up to 150 kG. Eleven different resistors having nominal values at room temperature of 47, 100, and 220 Ω were investigated. A description is given of a new technique which was devised to perform these measurements. The magnetoresistance of Allen-Bradley resistors is small, reproducible, and can be estimated from measurements on other resistors of the same nominal value. These resistors are useful, therefore, as thermometers in intense magnetic fields at low temperatures. A comparison is made between different empirical equations which have been used in attempts to fit the data. In addition, different methods are described for determining the temperature T and sensitivity R−1(∂R/∂T)H from the magnetoresistance data.