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

TLDR

The bcc Fe–Zr–B alloys exhibit saturation magnetization comparable to Fe‑6.5 % Si and permeability far exceeding that of Fe–Si, positioning them as promising soft magnetic materials. The study aims to develop a novel soft magnetic material by exploiting the combined high Bs and μe of the bcc Fe–Zr–B base alloys. A mostly single bcc phase with 10–20 nm grains was obtained by annealing, yielding μe >10 000 at 1 kHz and Bs >1.5 T, with peak values of 14 000 μe/1.70 T for Fe91Zr7B2 and 20 000 μe/1.55 T for Fe87Zr7B5Cu1, and 1 at % Cu further enhanced μe by reducing 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 (μe) above 10000 at 1 kHz combined with high saturation magnetization (Bs) 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 μe 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 Bs 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 μe values are much higher than that for the Fe–Si alloy. Accordingly, the combined characteristics of high Bs and μe values for the bcc Fe–Zr–B base alloys allow us to expect a subsequent development as a novel soft magnetic material.