Room-Temperature Weak Ferromagnetism Induced by Point Defects in α-Fe₂O₃

Unusual room-temperature weak ferromagnetism alpha-Fe(2)O(3) was prepared by heating the mixture of commercial alpha-Fe(2)O(3) (as raw material) and tartaric acid at a mild temperature of 250 degrees C. This reaction involves a fast heating and cooling process resulting from the self-catalyzed oxidation of tartaric acid. Careful chemical analyses confirmed that no any ferromagnetic impurities, such as Fe, Fe(3)O(4), amorphous iron oxide and gamma-Fe(2)O(3,) were present in the treated sample. The unusual weak ferromagnetism was then attributed to the formation of a large amount of point defects in the treated sample during the peculiar synthetic process. Such a mechanism is supported by the result of annealing, which reduces the amount of point defects and thereby reestablishes the original antiferromagnetism in alpha-Fe(2)O(3).