Phase transformations in iron oxide under the action of microwave radiation

It is shown that microwave radiation induces structure changes and, consequently, magnetic phase transitions in iron oxide $\alpha$-Fe$_2$O$_3$. We subjected finely dispersed partially amorphized particles of iron oxide Fe$_2$O$_3$ to 10-minute-long microwave field treatment in a humid air environment. This resulted in a reduction of the hematite crystalline phase by 40%. At the same time the total fraction of crystalline components increased due to the creation of a new ferromagnetic modification which is maghemite $\alpha$-Fe$_2$O$_3$. The original antiferromagnetic samples and the finial ferrimagnetic batches were powders composed of spherical particles with similar values of the area of a coherent X-ray scattering area (40–60 nm).