The effects of Co on the enhancement of magnetic properties by modifying the intergranular phase in Nd-Fe-B alloys

Y Liang,H Xu,Q Deng,X H Tan,H Li

doi:10.1038/s41598-018-36583-x

Abstract

In Nd2Fe14B-based permanent materials, the intergranular phase has a strong influence on magnetic properties. Here, we study the effect of partial substitution of Fe by Co on the microstructure to gain insight into the mechanism of enhancing magnetic properties of (Nd0.8Pr0.2)2.2Fe14−xCoxB (x = 0, 1.75, 2, 2.25) alloys. Our results show that the substitution Co for Fe changes the magnetic properties obviously by tuning the chemistry and distribution of the intergranular phase between hard magnetic grains. In particular, for (Nd0.8Pr0.2)2.2Fe12Co2B (x = 2) alloy, no obvious intergranular phase is observed. And the through-thickness homogeneity and ultrafine microstructure with an average size of ~25 nm is obtained, which produces maximum product ((BH)max) of 141 kJ/m3, 29% higher than that of quaternary alloy. Our findings provide a new idea to design prospective permanent alloys with increased magnetic properties by tuning the distribution and chemical composition of the intergranular phase.

Highlights

Nd2Fe14B-typed permanent magnets (PMs) have found applications in a wide range of fields including electronic, data processing and medical devices due to their outstanding hard magnetic properties[1,2]
Two different types of intergranular phase are observed: i) non-magnetic intergranular phase with large amount of rare earth metals (RE) (>65 at.%) which improves the coercivity by promoting a magnetic isolation of 2:14:1 grains[7]; and ii) ferromagnetic intergranular phase containing large fractions of Fe and/or Co more than 65 at.% leads to an improvement of remanence by enhancing the inter-grain coupling[8]
For non-magnetic intergranular phase of hot-deformed Nd-Fe-B magnets, substitution of Co for Fe led to the formation of a Co-enriched layer at the edges of 2:14:1 grains resulting in a reduction of the magnetocrystalline anisotropy of 2:14:1 phase[9], whereas the segregation of Co was found at the interface between the intergranular phase and 2:14:1 phase acting as nucleation sites for reversed magnetic domains[10]

Summary

Introduction

Nd2Fe14B-typed permanent magnets (PMs) have found applications in a wide range of fields including electronic, data processing and medical devices due to their outstanding hard magnetic properties[1,2]. Achievement of through-thickness homogeneity with an average size less than 50 nm in the ribbon microstructure during melt-spinning is extremely difficult due to some major factors including fabrication conditions and composition of alloys. Cu and Nb addition is reported to decrease the grain size effectively resulting in an improvement of magnetic properties of nanocomposite alloys[15]. We investigated the microstructure and magnetic properties of (Nd0.8Pr0.2)2.2Fe14−xCoxB (x = 0, 1.75, 2, 2.25) melt-spun ribbons to understand how Co-substitution for Fe could be employed to tailor the magnetic properties by tuning the distribution, type and chemistry of the intergranular phase. Partial substitution of Nd by Pr is chosen because Pr addition can promote uniform distribution of intergranular phase resulting in an increase of magnetic properties in Nd-Fe-B alloys[20,21]. It produces maximum product ((BH)max) of 141 kJ/m3, which is 29% higher than that of quaternary alloy

Methods

Results

Conclusion