|MadSci Network: Earth Sciences|
In fact, the magnetic domains in a magnet may be affected by two main factors: temperature and external magnetic fields. Temperature can easily destroy the magnetic domains and transform your magnet in a piece of a mettalic alloy. You can think about it in the terms of the state of movement of the particles, that increase with temperature, and, at a certain level, "break" the magnetic domains. Each material has a temperature called Curie Temperature, above which no magnetic domains can exist. For hematite, for example, it is around 600-650 Celsius. But you don't have to reach this temperature to destroy partially the magnetic domains, so, if you expose your magnet at high temperatures, it will be gradually "losing power". If you expose the material to a strong magnetic field the same effect can occur, because you are disturbing the alignment of the magnetic domains of the material. If you take care with your magnet, I guess it will be in the family for many generations... :) Best regards Eder C. Molina firstname.lastname@example.org Dept. of Geophysics Institute of Astronomy, Geophysics and Atmospheric Sciences University of Sao Paulo - BRAZIL
Try the links in the MadSci Library for more information on Earth Sciences.