Anisotropic bulk SmCo7 nanocrystalline magnets with high energy product

Wenpeng Song,Xiangyi Zhang,Yingxin Hua,Guangwei Huang,Qian Zhang,Xiaohong Li,Li Lou

doi:10.1063/1.4995507

Abstract

Realizing grain alignment along easy magnetization axis in bulk SmCo7 nanocrystalline materials is crucial for their development as high-performance high-temperature magnets, yet it remains challenging. Here, we report the fabrication of anisotropic bulk SmCo7 nanocrystalline magnets with a small grain size of ∼20 nm and a (00l) texture using high-pressure thermal compression starting from partially amorphous precursors. The synthesized magnet exhibits a high energy product of 18.4 MGOe, 40% larger than the reported highest value (13 MGOe) for bulk nanostructured SmCo7 magnets, and outperforms its anisotropic coarse-grained counterpart. Moreover, our magnet shows a low coercivity temperature coefficient of β = −0.19%/°C. These findings make an important step toward the fabrication of oriented bulk nanostructures for practical applications.

Highlights

The SmCo7 alloy with a TbCu7 structure has been found to have the potential to become a new class of high-temperature magnets due to the integrated large magnetocrystalline anisotropy (Ha = 100-180 kOe), high saturation magnetization (Ms = 12.1 kG), high Curie temperature (T c = 780 ◦C), and low coercivity temperature coefficients
The TbCu7-type SmCo7 phase exhibits a metastable structure that cannot be synthesized by general equilibrium methods; it decomposes into Sm2Co17 and SmCo5 phases at relatively low temperatures of about 600 ◦C,4,6 impeding its manufacturing
Much progress has been made in inducing crystallographic alignment in SmCo5 bulk nanocrystalline magnets applying hot deformation of the nanocrystalline precursors by die upsetting,[19,20] and a texture has been observed in the Sm9Zr3Co88 composition layers with the range of the “1:7 structure.”[21]. The pure TbCu7-type SmCo7 nanocrystalline structures with a small grain size of ≤20 nm and a crystallographic texture in bulk magnets have not been achieved until now

Summary

Introduction

Anisotropic bulk SmCo7 nanocrystalline magnets with high energy product The observed crystal anisotropy or isotropy in the HPTC deformed or high-pressure annealed sample is further supported by magnetic measurements (see below). To characterize the three-dimensional morphology of the oriented SmCo7 nanostructure, we carried out TEM observations on the two faces of the deformed sample: parallel and perpendicular to the pressure direction, which is a routine method for studying the morphology of nanograins in bulk materials.[27,28] The longitude-sectional TEM images show numerous lath-shaped grains

Results

Conclusion