Cerium-based RCo5 (R = Ce, La0.35Ce0.65, and misch-metal) type nanocrystalline hard magnetic materials with high coercivity

Wen-Liang Zuo,Tong-Yun Zhao,Ji-Rong Sun,J Ping Liu,Xue-Feng Zhang,Yong-Feng Li,Jeotikanta Mohapatra,Bao-Gen Shen,Feng-Xia Hu

doi:10.1063/1.5104295

Abstract

Nanocrystalline RCo5 (R = Ce, La0.35Ce0.65, and misch-metal noted as MM) ribbons with hexagonal crystal structure and an average grain size of 5 nm have been prepared via a one-step melt-spinning technique. Coercivity as high as 13.0, 13.8, and 10.9 kOe has been obtained at 300 K for the CeCo5, La0.35Ce0.65Co5, and MMCo5 ribbons, respectively. High thermal stability is also achieved as shown by the high coercivity of 9.3 kOe, 10.2 kOe, and 8.8 kOe at 400 K for CeCo5, La0.35Ce0.65Co5, and MMCo5 ribbons, respectively. The coercivity mechanism is studied by magnetization analysis and microstructural observations. The nanocrystalline grains promote a strong exchange interaction, as indicated by the positive δM and the relatively high remanence ratio (∼0.8). In addition, the temperature dependence of coercivity of RCo5 ribbons shows the low coercivity temperature coefficient of −0.2% to −0.25%/K.

Highlights

Among various rare-earth transition-metal intermetallic compounds, RCo5 (R = rare-earth elements) compounds are interesting due to their extremely high magnetocrystalline anisotropy and very high Curie temperature.1,2 The SmCo5 compound has the highest uniaxial magnetocrystalline anisotropy (20 × 107 erg/cm3) and is the major phase of the first generation of rare-earth permanent magnets.2 In comparison to SmCo5, the other RCo5 compounds possess similar inherent magnetic properties, they have not been used as permanent magnets because of technical difficulties in achieving proper microstructures necessary for developing high coercivity
The art of making high coercivity magnetic materials is to control the microstructure at the nanoscale
To reduce the grain size is of paramount importance for obtaining high performance in hard magnetic materials

Summary

Introduction

The SmCo5 compound has the highest uniaxial magnetocrystalline anisotropy (20 × 107 erg/cm3) and is the major phase of the first generation of rare-earth permanent magnets.. In comparison to SmCo5, the other RCo5 compounds possess similar inherent magnetic properties, they have not been used as permanent magnets because of technical difficulties in achieving proper microstructures necessary for developing high coercivity. CeCo5 exhibits quite high magnetocrystalline anisotropy (7.2 × 107 erg/cm3), the reported magnetic coercivity reaches only 3%–5% of the corresponding anisotropy field (Hk).. Recent research for the new economical alternatives to the current commercial rare-earth permanent magnets showed that despite having the mixed Ce3+/Ce4+ valency problem, typically adverse for the magnetocrystalline anisotropy, the Ce-substituted Nd2Fe14B magnet systems are comparable with the commercial high-flux grade magnets and have lower material cost.. The coercivity of the prepared RCo5 hard magnetic materials is low. Recent research for the new economical alternatives to the current commercial rare-earth permanent magnets showed that despite having the mixed Ce3+/Ce4+ valency problem, typically adverse for the magnetocrystalline anisotropy, the Ce-substituted Nd2Fe14B magnet systems are comparable with the commercial high-flux grade magnets and have lower material cost. Attempts have been made to replace Sm by Ce or La, or other low cost mixed rare-earths like MM (25–35 wt. % La, 45–55 wt. % Ce, 4–10 wt. % Pr, 14–18 wt. % Nd) in SmCo5-type magnets. the coercivity of the prepared RCo5 hard magnetic materials is low.

Methods

Results

Conclusion