The magnetic susceptibility of a substance (for example, a soil sample) is analyzed by placing the sample in a measurement cell where a magnetic field is applied. Depending on the magnetic properties of the substance, the magnetic field is affected by being either enhanced, weakened, or not influenced at all. Dipolar compounds have properties that weaken an applied magnetic field (for example, water). The same applies to many organic compounds, such as peat and humus, which exhibit diamagnetic properties. Substances with permanent magnetic properties significantly enhance the applied magnetic field (for example, a compass needle). Between these extremes are paramagnetic substances, which only exhibit magnetic properties when influenced by a magnetic field. In the soil, there are several forms of iron oxides with varying properties in magnetic susceptibility, and it is these that are analyzed in archaeological contexts. The technique can be used both in the field and in the lab.
