Nanocrystalline Hf and Ta containing FeCo based alloys for high frequency applications

FeCo based nanocrystalline materials have excellent soft magnetic properties even at high temperature, but are limited to low frequency applications due to their relatively low electrical resistivities, ρe, resulting in high eddy current losses. Amorphous alloys of (Fe81Co19)84M9B7 where M = (Hf, HfTa, Ta) were prepared by meltspinning and annealed for increasing times at their respective crystallization temperatures. The nanocrystalline alloys had coercivities less than 0.4 Oe and saturation inductions greater than 1 T. The electrical resistivities of the amorphous ribbons were all similar with values of ρe ≃ 180 μΩ cm. After annealing at the crystallization temperature, the M = Ta alloy had the largest ρe of 140 ± 3 μΩ cm. The Ta alloy also had the best high frequency properties, with an initial permeability of 822 at 1 MHz.

► Nanocrystalline alloys with nominal compositions (Fe81Co19)84M9B7, where M = Hf, HfTa, and Ta, were produced by heat treating amorphous ribbons.
► Ta additions reduce eddy current loss by increasing the resistivity, enabling higher frequency operation.
► A reduction in grain size is observed by X-ray diffraction for the Ta containing alloys, leading to better soft magnetic properties.