To date, an extensive research has been carried out on the synthesis and applications of magnetically recoverable nanomaterials such as Fe3O4 and Fe2O3 due to their unique magnetic properties. Will it be useful, if the mixed iron oxides made up of both ferrite and hematite?
Dear U. Chinna Rajesh: maghemite + magnetite is used as magnetic recording medium for recording information.2Fe3O4 + 0,5O2=3Fe2O3. The reaction is reversible.
The preparation of pure magnetite Fe3O4 is difficult and has to be done under controlled condition. If the atmosphere is slightly oxidising during the preparation of Magnetite, Fe2O3 would automatically appear. So by control of the atmosphere as regards its Oxygen content it is possible to prepare this two phase material.
gamma-Fe2O3 and Fe3O4 actually are the end points of a continuous stoichiometry range of spinel type iron oxides. My source for that is:
E. Pellegrin et al., phys. stat. sol. (b) 215, 797 (1999)
Now, hematite (alpha-Fe2O3) is an iron oxide with a different structure and magnetic properties. magnetite/maghemite are ferrimagnetic, while hematite is an antiferromagnet. I have not encountered any mixtures of hematite and spinel oxides but also never searched for such a material. Whether this might be useful will certainly depend on the level of control you can achieve concerning the geometrical arrangement of the different oxides and the resulting magnetic coupling. Certainly, such coupling sould should exist to make the material useful. Coupling ferrimagnets and antiferromagnets one might think of exchchange biased materials, or spin valves for example. How useful this could be given that hematite is alo insulating (as far as I recall), might yet be another subject to consider.
I grew Hematite/Magnetite bilayers onto sapphire during my PhD. As already said the thermodynamics of it is quite tricky and growing controlled samples was extremely difficult. In practice we had an uncontrolled mix of the two phases. TEM images showed the thickness of hematite at the end varied between zero and the whole film thickness, for reasons we never figured.
So in the end we dropped it and tried to find something else to obtain exchange bias. We did not publish it a the time, because it was a negative result.
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