ac bridge for high-temperature magnetic thermometry

Abstract

A modified Hartshorn inductance bridge is used to follow changes in the magnetization of superparamagnetic samples in order to determine their average temperature. The thermometry is performed in the temperature range of 475–525 K. During routine experiments, the rms noise voltage in the bridge is approximately 300 nV when the primary coil is excited by a 200 mA rms current at a frequency of 47 Hz. This corresponds to a signal-to-noise ratio of 3000 and a temperature sensitivity of 0.015 K for typical samples studied.