High-temperature magnetic susceptibility bridge

Abstract

A low-field (0.31 Oersted peak) a.c. susceptibility bridge has been built. Volume susceptibilities as low as 7 x 10⁻⁸ emu/cc are detectable. -- The bridge was calibrated over the range 10⁻⁶ - 10⁻² emu/cc using two independent methods, namely (1) paramagnetic salts, and (2) a 40 - turn coil. The two methods gave very good agreement. -- A furnace, capable of attaining 800°C, was added to the bridge, so that susceptibility could be measured as a function of temperature. The furnace was made of non-magnetic Chromel-A heater wire and wound non-inductively. -- Errors in room temperature susceptibility readings range from 2% for k ∿ 1 X 10⁻² emu/cc to 20% for k ∿ 1 x 10⁻⁷ emu/cc. At present, room temperature susceptibilities of less than 4 x 10⁻⁵ emu/cc cannot be measured to better than 20% as a function of temperature due to more serious restrictions during heating. -- Possible improvements in the equipment capable of reducing these errors, as well as alterations to extend the usefulness of the apparatus, are discussed. -- Specimens from several different rock types including lava flows, ignimbrites, red sandstones and dykes were subjected to high temperature susceptibility measurements in air. Results from these measurements generally confirm the results obtained from studies of Curie points and other rock magnetic properties by various authors.