An easy-plane FeSi3.5 composite with excellent magnetic properties and loss properties at MHz were proposed. The easy-plane FeSi3.5 composite has ultra-low loss at 10 MHz and 4 mT, about 372.88 kW/m3. In order to explore the reason that the Pcv of easy-plane FeSi3.5 composite is ultra-low, a none easy-plane FeSi3.5 composite, without easy-plane processing as a control group, measured the microstructure, and the magnetic and loss properties. We first found that the real reason why magnetic materials do not work properly at MHz due to overheat is dramatical increase of the excess loss and the easy-plane composite can greatly re-duce the excess loss by loss measurement and separation. The total loss of none easy-plane FeSi3.5 composite is much higher than that of easy-plane FeSi3.5 composite, where the excess loss is a major part in the total loss and even over 80% in the none easy-plane FeSi3.5 composite. The easy-plane FeSi3.5 composite can greatly reduce the total loss compared to the none easy-plane FeSi3.5 composite, from 2785.8 kW/m3 to 500.42 kW/m3 (3 MHz, 8 mT), with the main reduction being the excess loss, from 2435.2 kW/m3 to 204.93 kW/m3 (3 MHz, 8 mT), reduced by 91.58%. Furthermore, the easy-plane FeSi3.5 composite also has excellent magnetic properties, high permeability and ferromagnetic resonance frequencies. This makes the easy-plane FeSi3.5 composite become an excellent soft magnetic composite and it is possible for magnetic devices to operate properly at higher frequencies, especially at the MHz band and above.
Keywords: MHz frequency band; easy-plane soft magnetic composites; excess loss; ultra-low power loss.