Microstructure and magnetic properties of two-phase nanocomposite Nd9Fe85.5Nb1.0B4.5−yCy (y=0.5–4.5) magnets

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Abstract

Nanocrystalline two-phase Nd9Fe85.5Nb1.0B4.5−yCy magnets (y=0.5–4.5) have been prepared by melt spinning and subsequent heat treatment. The effect of remanence enhancement has been observed in the melt-spun ribbons after a proper annealing procedure. A two-phase nanocomposite Nd9Fe85.5Nb1.0B4.0C0.5 magnet with optimum magnetic properties of Hcj=6.6 kOe, Jr=10.22 kGs and (BH)max=13.32 MGOe has been obtained.

Introduction

Nd2Fe14C might be developed into a new rare-earth permanent magnet as it possesses a high room temperature magnetocrystalline anisotropy (μ0Ha=9.5 T), high saturation magnetization (Ms=1.50 T) and high ideal energy product (BH)max=56.2 MGOe [1], [2]. Especially, Nd2Fe14C has a higher anisotropy field and coercivity than its counterpart Nd2Fe14B. In the past years, many investigations were focused on the microstructure and magnetic properties of ingots of Nd2Fe14C formed by arc-melting and a long time heat treatment [3], [4], [5]. Recently, results of studies on ball milling Nd2Fe14C were reported [6], [7]. However, relatively little is known about producing Nd2Fe14C and Nd2Fe14C/α-Fe nanocomposite magnets by melt-spinning. In addition, two-phase nanocomposite magnets have received considerable attention and have become a hot topic because of a very high theoretical energy product (BH)max∼120 MGOe and low costs of rare earths, which may lower the costs for the industrial manufacture [8]. It is therefore useful to study Nd2Fe14C/α-Fe nanocomposite materials both on scientific and practical grounds.

Section snippets

Experimental

Three series of ingot samples, with a nominal composition of Nd9Fe85.5Nb1.0B4.5−yCy (y=0.5–4.5), were prepared by arc-melting the pure constituent elements of Nd, Fe, Co, Nb and Fe–B, Fe–C prealloys in an argon atmosphere. The ingots were remelted for 3 min to ensure a good homogeneity. Portions of the ingots were melted in a quartz tube, heated by an induction current, and then rapidly quenched onto a water-cooled copper wheel with a roll speed of 5–45 m/s. The resulting ribbons, with 3–30 mm

Results and discussion

The as-spun ribbons consist of crystalline Nd–(Fe,Nb)–(B,C) and α-Fe at a low spinning speed, i.e. less than 15 m/s (see Fig. 1). It is clearly seen from Fig. 1 that the mixture of the as-spun ribbons are composed of both the crystalline 2:14:1 phase and some amorphous materials at v=15 and 20 m/s. The crystalline phase disappears and an amorphous phase is formed when the wheel speed is increased to 30 m/s. The same result is found by thermomagnetic analysis of the as-spun ribbons (see Fig. 2).

Acknowledgments

This work is supported by the China Postdoctoral Science Foundation and the National Science Foundation of China.

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