Magnetization, Thermoremanent, in Minerals
Perhaps the best understood of the primary magnetizations, of natural rocks and specimens, is thermal remanent magnetization (TRM). Most of the natural rocks are magnetized primarily by the geomagnetic field (∼30 000 nT) and acquire natural remanent magnetization (NRM). Magnetic minerals acquire TRM when they are contained within the rock that is cooled in an external magnetic field from temperatures above the minerals’ blocking temperatures. Blocking of remanent magnetization at a specific temperature results in locking of a specific direction and intensity of magnetization as it becomes stable on the timescale of the TRM acquisition.
The generally recognized first‐order theory of TRM can be applied only to small uniformly magnetized grains (Néel, 1949) and it provides a reasonable explanation for the intensity of TRM vs inducing field. The theory explains the changes of stability of TRM with temperature and with the inducing field, explaining how a rock...
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