Achievement of approximate 1.9 T in coercivity and coercivity enhancement mechanism in Nd,Ce-Fe-B-Ga alloy ribbons

Abstract

Enhancing the utilization of abundant rare earth elements to produce Nd-Fe-B based magnets with superior permanent magnetic properties remains a significant research focus in the field of rare earth permanent magnets. In this study, we propose an effective approach to significantly improve the coercivity of Nd,Ce-Fe-B-Ga ribbons. Ribbons with nominal compositions of [(1–x)(Nd_0.5Ce_0.5)_11.76Fe_82.35B_5.88 + xNd₃₀Fe₆₅Ga₅] (at%; x = 0, 0.1, 0.2, and 0.3) were fabricated via melt-spinning. Hysteresis loops at ±2 T reveal obvious exchange bias phenomena in all samples except for x = 0, which originates from the exchange coupling effect between the ferromagnetic (FM) phase and the antiferromagnetic (AFM) phase. Under an applied field of ±5 T, the coercivity increases progressively from 6.55 kOe (x = 0) to 18.98 kOe (x = 0.3). Specifically, the sample of x = 0.1, where Ce accounts for 38.96 at% of the total rare earth content, achieves a coercivity of 14.46 kOe. The absolute values of the temperature coefficients of remanence (α) and coercivity (β) decrease from 0.420%/K (x = 0) to 0.334%/K (x = 0.2) and from 0.708%/K (x = 0) to 0.439%/K (x = 0.2), respectively. The transmission electron microscopy (TEM) characterization shows that in the Ga-free ribbons (x = 0), grains of the main phase RE₂Fe₁₄B are continuously surrounded by a thin RE-rich grain boundary (GB) phase. With Ga addition (x = 0.3), the continuous RE-rich GB phase disappears and large-sized triple junction phases form, which are composed of the RE-rich phase and the RE₆Fe₁₃Ga phase. Henkel plots further confirm the strong intergranular exchange coupling effect. Therefore, we propose a coercivity enhancement mechanism, namely, the reversal of magnetic domains is pinned through the exchange coupling effect between the AFM phase and the FM phase, thereby enhancing the coercivity of the magnet.