I. Introduction
Many inductive source time-domain electromagnetic (TEM) systems use a step-offlike excitation to measure the response from a desired target. In lateritic soils, sudden removal of the transmitter’s primary field induces a time-dependent magnetic relaxation due to the presence of superparamagnetic (SP) iron-oxide grains [1]–[5]. This magnetic relaxation process is known as viscous remanent magnetization (VRM), magnetic viscosity, or magnetic aftereffect [6]–[8]. The VRM experienced by a lateritic soil generates a distinct transient response from that of a nonmagnetic conductive soil. This response, termed the VRM response, can severely contaminate the TEM responses from conductive ore bodies and unexploded ordnance items when lateritic soils are prominent [1]–[5], [9]. Thus, to properly account for the VRM signal in a set of TEM data, it is of practical interest to first understand the behaviors of the VRM response.