The measurement of magnetic hysteresis in rocks and minerals at high temperatures

Abstract

An experimental method is described, designed chiefly to furnish data for a study of the direction, and stability with time, of thermoremanence in rocks. Specimens were heated to the Curie point in an evacuated electric furnace. Two pick-up coils were arranged close to the gap of a tuned a. c. electromagnet providing a maximum field H of 2400 oersteds. These were balanced to make their resultant e. m. f. zero in the presence of H alone, and proportional to dI/dt when a specimen of intensity of magnetization I was in the gap. This e. m. f. was applied to the vertical plates of a cathode ray oscilloscope. The potential drop over a small resistance in the electromagnet input was applied to the deflection coils, giving a measure of H. Computations based on the resulting pattern on the c. r. o. screen yield a loop of the I-H type, with I in arbitrary units, from which the coercivity can be evaluated. A pronounced “sawtooth” pattern has been observed in the (dI/dt)-H traces of pyrrhotite and franklinite specimens, particularly just below the respective Curie points. © 1956, Society of Geomagnetism and Earth, Planetary and Space Sciences. All rights reserved.