The use of the 'Kono perpendicular applied field method' in microwave palaeointensity experiments

For a complete understanding of the Earth's magnetic field behaviour it is necessary to have information regarding variations in its strength as well as directional changes. In order to reduce the lengthy experimental time for palaeointensity experiments and potentially reduce the possibility of mineralogical alteration Kono suggested a single heating perpendicular applied field variant of the most widely used double heating palaeointensity method (the Thellier method). Whilst in the past this method has not been generally used, due mainly to technical difficulties. it is ideal for use with the microwave palaeointensity technique. Reproducing the amount of microwave energy absorbed by a sample is not as simple as reproducing the temperature in an oven so a palaeointensity method that only has a single application of microwave power at each step is an advantage. One of the uncertainties in the original Kono method ties in getting the natural remanent magnetisation of the sample aligned perpendicular to the applied laboratory field. With the microwave systems this uncertainty has been essentially removed. The microwave variant of the perpendicular applied field method which incorporates checks for perpendicularity, as well as the usual checks for alteration and non ideal behaviour is routinely applied as it is quick and easy to use, avoids any potential power reproducibility issues and provides a comparison with results obtained through other methods.