Magnetic ferrites such as Fe304 and Fe 203 are extensively used in a range of applications because they are inexpensive and chemically stable. Here we show that rhodium-substituted E-Fe203, E-RhxFe2—x03 nanomagnets prepared by a nanoscale chemical synthesis using mesoporous silica as a template, exhibit a huge coercive field (Hc) of 27 kOe at room temperature. Furthermore, a crystallographically oriented sample recorded an Hc value of 31 kOe, which is the largest value among metal-oxide-based magnets and is comparable to those of rare-earth magnets. In addition, E-RhxFe2—x03 shows high frequency millimetre wave absorption up to 209 GHz. E-RhO. .8603 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.