Time‐domain magnetization of soils (VRM), experimental relationship to quadrature susceptibility

Abstract

A comparison is made between measurements with a multichannel bipolar pulsed‐induction meter (PIM) and measurements made with a phase‐sensitive susceptibility bridge on more than 211 soil samples from a variety of archaeological sites in Europe. Eddy currents originating from the decay of viscous remanent magnetization (VRM) were measured with the PIM. The in‐phase and out‐of‐phase [Formula: see text] magnetic mass susceptibilies were measured with the susceptibility bridge. Viscous remanent magnetization was measured through eight time sampling intervals on the pulsed‐induction meter, and the linearity of VRM for selected samples was tested at various field strengths (200 to 2300 μT). It is believed that this extension of the reversible range indicates a high coercive strength of the magnetic grains in the soil samples involved. Whatever the origin of the soil sample, a constant decay of VRM with time was observed between 56 and 417 μs, after switching off the inducing field. This relation is shown to be a power law with exponent −1.4. This roughly agrees with a theoretical model that takes into account a finite‐energizing time of the transmitter pulse and single‐domain (SD) behavior of particles. Finally, a comparison is made between VRM and quadrature susceptibility [Formula: see text]. This comparison is in accordance with well dispersed single‐domain theory, and was found to be a linear relationship.