Hard magnetic ferrite with a gigantic coercivity and high frequency millimetre wave rotation

Magnetic ferrites such as Fe3O4 and Fe2O3 are extensively used in a range of applications because they are inexpensive and chemically stable. Here we show that rhodium-substituted epsilon-Fe2O3, epsilon-RhxFe2-xO3 nanomagnets prepared by a nanoscale chemical synthesis using mesoporous silica as a template, exhibit a huge coercive field (H-c) of 27 kOe at room temperature. Furthermore, a crystallographically oriented sample recorded an H-c value of 31 kOe, which is the largest value among metal-oxide-based magnets and is comparable to those of rareearth magnets. In addition, epsilon-RhxFe2-xO3 shows high frequency millimetre wave absorption up to 209 GHz. epsilon-Rh0.14Fe1.86O3 exhibits a rotation of the polarization plane of the propagated millimetre wave at 220 GHz, which is one of the promising carrier frequencies (the window of air) for millimetre wave wireless communications.