Natural Science and Engineering Research Council of Canada (NSERC); National Natural Science Foundation of China [20725310, 20673085]; National Basic Research Program of China [2007CB815303]Unusual room-temperature weak ferromagnetism alpha-Fe2O3 was prepared by heating the mixture of commercial alpha-Fe2O3 (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. Fe3O4, amorphous iron oxide and gamma-Fe2O3, 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-Fe2O3
