Low Temperature Thermometry in High Magnetic Fields. II. Germanium and Platinum Resistors

Abstract

The effect of static magnetic fields up to 210 kG on the characteristics of commercial germanium and platinum resistance thermometers was measured at various temperatures in the range 3.5–78 K. Measurements of the transverse (sample current I normal to magnetic field H) and longitudinal (I∥H) magnetoresistance were carried out on both types of thermometers. A description is given of the dc resistance measuring technique used in these experiments. This method is a semiautomatic potentiometric scheme which increases the speed of measurement while maintaining high resolution and reasonable accuracy. The magnetoresistance of the germanium sensors was found to be large and orientation dependent over the temperature range investigated. These effects preclude the use of germanium elements, as presently fabricated, for temperature sensors in a high magnetic field environment. In the case of platinum resistance thermometers, the magnetoresistance at temperatures above 30 K is small enough so that it becomes practical to correct for it. In fact, these thermometers have been recently used in studies of the magnetic phase transitions in antiferromagnets in fields up to 200 kG.