Low temperature magnetic hysteresis of fine particle aggregates occuring in some natural samples

Hysteresis loops of basaltic rocks which usually have aggregates of magnetic particles have been studied in the temperature range 25° to −190°C. Some samples showed coercive forces as high as 930 oe at −190°C. Blocking temperature studies of the magnetic grains in these samples revealed that they contain particles, most of which are superparamagnetic at or around room temperature. The studies are consistent with the inference that very fine titanomagnetite particles are responsible for the observed behaviour of the samples.