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It has been found that goethite acquires a thermoremanent magnetization (TRM) when cooled in the presence of a magnetic field from 120°C. It is believed that this TRM is due to the presence of antiferromagnetism in goethite with a Nee1 temperature of 120°C. A few spins have no mates because of small grain size or the presence of imperfections and impurities.Similarly, hematite acquires a TRM at its Nee1 temperature which is due to unbalanced spins. In addition hematite is known to have a ' parasitic ferromagnetism '. Hematite derived from heating goethite above 350°C showed two different types of behaviour. Hematite composed of particles less than +,i diameter showed no spontaneous magnetization, but did show a weak thermoremanence whereas hematite composed of larger particles developed a spontaneous magnetization. These observations indicate that parasitic ferromagnetism exists only in graiiis larger than +p.This TRM is related to antiferromagnetism.

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Goethite, known to be antiferromagnetic, acquires thermoremanent magnetization at its Neel temperature of 120 degrees C. This remanence, extremely stable, is due to the presence of unbalanced spins in the antiferromagnetic structure; the spins may result from grain size, imperfections, or impurities.

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