The anomalous demagnetization of pyrrhotite

Abstract

The anomalous behaviour of pyrrhotite‐bearing rocks from the Pennine Orefield, northern England on alternating field demagnetization is studied with particular reference to rotational remanent magnetization (RRM). Using a heat treated sample, it is demonstrated that a two‐axis tumbling demagnetizer is capable of producing a repeatable RRM along its inner axis of rotation which is comparable in strength to that produced in an instrument which uses single axis rotation and which is specifically designed to produce a RRM. The unheated samples gave a scattered RRM which was of sufficient intensity to disturb the primary magnetization. After heating the RRM become reproducible, much larger and parallel to the rotation vector for rotation rates between 1.5 and 120 rev s‐1 for an AF frequency of 50 Hz. This behaviour is unlike all previously measured samples, whether oxides or sulphides, by other workers. The source of the anomalous RRM and the change in RRM with heating are discussed with reference to the physical structure and the strong magnetocrystalline anisotropy in pyrrhotite. Copyright © 1990, Wiley Blackwell. All rights reserved