High Saturation Magnetization and Soft Magnetic Properties of bcc Fe–Zr–B and Fe–Zr–B–M (M=Transition Metal) Alloys with Nanoscale Grain Size

Abstract

A mostly single bcc phase with nanoscale grain sizes of 10 to 20 nm was found to form by annealing amorphous Fe–Zr–B, Fe–Zr–B–Cu and Fe–Zr–B–Cu–M (M=Hf, Nb or Ta) alloys for 3.6 ks in the range of 750 to 900 K. The composition range of the bcc phase extends from 5 to 7%Zr and 1 to 8%B for the Fe–Zr–B system and 5 to 8%Zr and 1 to 16%B for the Fe–Zr–B-1%Cu system. The bcc alloys exhibit high permeability (μ_e) above 10000 at 1 kHz combined with high saturation magnetization (B_s) above 1.5 T and the highest values reach 14000 and 1.70 T for Fe₉₁Zr₇B₂ and 20000 and 1.55 T for Fe₈₇Zr₇B₅Cu₁. The addition of 1 at% Cu causes an enhancement of μ_e through the decrease of the bcc grain size from 20 to 10 nm, in addition to an extension of the formation range of the bcc phase. It should be noted that the highest B_s value is almost comparable to that for Fe-6.5 mass% Si and considerably higher than those of other practical soft magnetic materials while the μ_e values are much higher than that for the Fe–Si alloy. Accordingly, the combined characteristics of high B_s and μ_e values for the bcc Fe–Zr–B base alloys allow us to expect a subsequent development as a novel soft magnetic material.