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, rho(e), resulting in high eddy current losses. Amorphous alloys of (Fe(81)Co(19))(84)M(9)B(7) 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 rho(e) similar or equal to 180 mu Omega cm. After annealing at the crystallization temperature, the M = Ta alloy had the largest rho(e) of 140 +/- 13 mu Omega cm. The Ta alloy also had the best high frequency properties, with an initial permeability of 822 at 1 MHz. (C) 2011 Elsevier BM. All rights reserved.