High-coercivity magnetic minerals in archaeological baked clay and bricksстатья
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Дата последнего поиска статьи во внешних источниках: 24 февраля 2021 г.
Аннотация:The thorough understanding of magnetic mineralogy is a prerequisite of any successfulpalaeomagnetic or archaeomagnetic study. Magnetic minerals in archaeological ceramics andbaked clay may be inherited from the parent material, or, more frequently, formed during thefiring process. The resulting magnetic mineralogy may be complex, including ferrimagneticphases not commonly encountered in rocks. Towards this end, we carried out a detailed rockmagnetic study on a representative collection of archaeological ceramics (baked clay fromcombustion structures and bricks) from Bulgaria and Russia. Experiments included measurementof isothermal remanence acquisition and demagnetization as a function of temperature between20°C and >600°C. For selected samples, low-temperature measurements of saturation remanenceand initial magnetic susceptibility between 1.8 K and 300 K have been carried out. All studiedsamples contain a magnetically soft mineral identified as maghemite probably substituted by Ti,Mn and/or Al. Stoichiometric magnetite has never been observed, as evidenced by the absence ofthe Verwey phase transition. In addition, one or two magnetically hard mineral phases have beendetected, differing sharply in their respective unblocking temperatures. One of these unblockingbetween 540°C and 620°C is believed to be substituted hematite. Another phase unblocks atmuch lower temperatures, between 140°C and 240°C, and its magnetic properties correspond toan enigmatic High Coercivity, Stable, Low-unblocking Temperature (HCSLT) phase reported