Investigation of Geomagnetic Orientation Preserved in a Stain Containing Iron Compounds Using a Vector-Type SQUID Magnetometer

We investigate the orientation of the magnetic field preserved in a stain containing iron compounds, such as ink pigment or blood, using a superconducting quantum interference device (SQUID) magnetometer system. The magnetization of a cloth or paper sample is observed by applying a vector-type SQUID gradiometer, which detects three orthogonal components of the magnetic field, and mechanical modulation, which converts dc magnetic signals to time-varying signals detectable by SQUIDs. Numerical experiments indicate that the orientation of the magnetization could be identified by the vector-type SQUID magnetometer when the sample was moved linearly under the probe. This paper describes in detail the instrumentation of the measurement system and a proof-of-principle experiment to confirm the system's effectiveness. The obtained results suggest that the magnetization of iron-compound-containing stains preserved the orientation of the magnetic field in which they were produced, as we hypothesized.