Thermomagnetic behaviour of haematite and goethite as a function of grain size in various non-saturating magnetic fields

When interpreting thermomagnetic curves of non-saturated magnetic minerals, irreversible heating and cooling curves need not necessarily imply chemical or structural changes. Increased aligning of magnetic moments on heating in an applied magnetic field can also induce an irreversible cooling curve. The two processes can be distinguished by stirring the sample between subsequent thermomagnetic runs. Sample redispersion considerably enhances the interpretative value of thermomagnetic analysis and is therefore strongly recommended, in particular when analysing non-saturated magnetic minerals.