thermoremanent

Thermoremanent magnetization (TRM) is a form of remanent magnetization that rocks and minerals acquire as they cool through their Curie temperature in the presence of an external magnetic field. In ferromagnetic minerals such as magnetite, heating above the Curie temperature destroys magnetic order; during cooling, magnetic domains align with the ambient field and become fixed as the temperature falls below the blocking temperature, preserving the field’s orientation and, to a degree, its intensity at the time of cooling.

TRM is most commonly studied in igneous rocks that crystallize from molten lava, as well as in fired archaeological materials such as pottery and bricks that were heated and then cooled in the Earth’s magnetic field. Because it records the ambient geomagnetic field at the time of cooling, TRM is a fundamental basis for paleomagnetic and archaeomagnetic reconstructions, enabling insights into past plate motions, geomagnetic reversals, and regional field behavior.

Thermoremanent magnetization is one component of thermoremanent magnetization phenomena and is distinct from other forms such as chemical remanent magnetization (CRM) and isothermal remanent magnetization (IRM). TRM is acquired during cooling through the Curie point, whereas IRM is acquired at a fixed temperature below Curie in a magnetic field, and CRM arises from chemical changes in minerals. The magnitude and direction of TRM depend on cooling rate, field strength, mineralogy, grain size, and the thermal history of the specimen.

Applications include dating and correlating volcanic and archaeological materials, reconstructing past geomagnetic field configurations, and contributing to magnetostratigraphic frameworks. Careful demagnetization and fitting procedures are used to isolate the TRM component from other magnetization signals.