An Investigation of the Role of Ultra-fine Titanomagnetite Intergrowths in Palaeomagnetism

Summary Grain subdivision by the development of intergrowth structure is shown to affect the remanent magnetic properties of the magnetite-ulvospinel system. The presence of ultra-fine intergrowths, visible only by electron microscopy, in naturally occurring material causes the magnetic remanence to be almost five times‘harder’ than that of experimentally homogenized material. These observations are attributable to the greater mobility of domain walls in the multi-domain homogenized samples, in contrast to the intergrown material which may be dominated by single-domain behaviour. The greater time stability which is expected to result from the increased‘hardness’ suggests that intergrowth structures can have palaeomagnetic importance.