P.O. Jubert, R. Allenspach, et al.
Physical Review B - CMMP
The natural remanent magnetization of andesitic pumice erupted from the Nevado del Ruiz volcano (Colombia) in 1985 is reversed with respect to the present geomagnetic field because of self-reversal. Laboratory thermoremanent magnetization acquired in fields of < 1 mT fully re-establishes the self-reversal mechanism. Hysteresis experiments indicate that the mechanism is caused by antiparallel coupling as a result of exchange interaction in two haemoilmenite phases of different composition. The weak critical field needed to suppress this self-reversal effect (≈ 1.2 mT) can be explained by a domain wall model. © 1990.