The cooling-rate effect on microwave archeointensity estimates

New microwave (MW) paleointensity data on historical bricks from Northeast Brazil presented a bias toward higher fields when compared to previous cooling‐rate corrected double‐heating paleointensity estimates; the same relates to the previously reported values for pottery from Southwestern Pacific islands. A simple theoretical approach suggests that the MW bias in both collections is due to a cooling‐rate effect on MW estimates. We then experimentally corrected the MW cooling‐rate effect on Brazilian fragments, increasing the degree of consistency between the previous and new results (reducing discrepancies from 25% to 8%). Results indicate similar experimental behavior between microwave and thermal procedures despite the different ways in which the energy is transferred into the spin system. Finally, they allow cooling times of less than 90 s to be empirically estimated in most of these MW experiments highlighting the need for systematic cooling‐rate corrections to be applied in similar MW paleointensity studies in the future. Key Points Cooling‐rate correction was successful applied on MW archeointensity data sets TT and MW cooling‐rate effects have similar physical behavior Difference of cooling times is a significant source of bias on MW estimates