Holey hematite!
15 Oct 2008



Transforming magnetism in a-Fe2O3 through mesostructure.

HRTEM image of mesoporous Fe2O3 with neutron diffraction patterns of bulk (top) and mesoporous forms (bottom) at 150K. The (111) reflection characterises different magnetic structures.

Liquid crystal templates have been used to mould hematite into porous structures and change its magnetic properties.

One of the most fascinating recent developments in solid-state chemistry is the use of liquid crystal templates to make moulds in which mesostructured forms of a wide range of materials may be grown. One such material is a-Fe2O3 (hematite), which may be synthesised in an ordered crystalline mesoporous form with 3.85nm diameter pores. Neutron powder diffraction studies on Osiris have shown that its collective magnetic properties are quite different from the standard, fully-dense form.

Bulk hematite undergoes the characteristic Morin transition at ~265K, transforming from a canted antiferromagnet with a weak ferromagnetism to a fully antiferromagnetic form with no spontaneous moment. In contrast, this particular mesoporous form displayed no such transition down to 1.5K, retaining its weakly ferromagnetic structure. The suppression of the Morin transition is also seen in nano-particulate hematite, but there the long-range magnetic order is also lost.

This change in the collective magnetic behaviour of hematite poses interesting questions about the influence of the mesostructure, and may also provide a means of conferring useful functionality on this and wider range of magnetic materials.

A Harrison

Research date: December 2006

Further Information

F Jiao et al., J. Am. Chem. Soc. 128 (2006) 5468.

Professor A Harrison (a.harrison@ed.ac.uk)​