What Does the Archaeomagnetic Record of Fired Ceramics Reflect?

Abstract—A complex of archaeomagnetic and rock magnetic studies is conducted to compare the archaeomagnetic intensity determined by the Thellier–Coe and Wilson methods with the known “true” value of the geomagnetic field during the firing of the ceramic samples manufactured on February 21, 2017 in the town of Myshkin (Yaroslavl oblast, Russia). The results obtained show two different values of archaeomagnetic intensity corresponding to two temperature intervals. The archaeomagnetic intensity estimated from the low-temperature interval (~150–350°C) are approximately 13 μT lower than the true value, while the values obtained in the interval of ~350–600°C are fairly close to the “true” ones. The cause of the phenomenon is likely due to the presence of small magnetic grains in the ceramic under study, which are close in size to superparamagnetic ones and can resume their growth upon heating and reaching a particle size in a single-domain state. The results of rock magnetic studies suggest that thermoremanent magnetization in the studied ceramics is carried by grains of oxidized magnetite, hematite, and possibly ε-Fe₂O_3.