Presentation Information
[P2-63]Low-Temperature-Phase MnBi Nanocomposite Magnets for Rare-Earth-Free Permanent Magnet Applications
*Jian WANG1, Wataru YAMAGUCHI1, Yusuke HIRAYAMA1 (1. National Institute of Advanced Industrial Science and Technology (AIST) (Japan))
Keywords:
rare earth free magnet,MnBi,nanocomposite,powder,thermal plasma
Low-temperature-phase MnBi alloy, a promising rare-earth-free permanent magnet, has garnered significant attention for its potential in high-temperature applications such as electric vehicle motors and wind turbines. However, its inherent limitation of low intrinsic magnetization, resulting in a low maximum energy product ((BH)max), hinders its practical implementation [1]. One effective strategy to mitigate this issue involves the fabrication of hard/soft composite magnets, which synergistically combine the advantages of both magnetically hard and soft materials.
In this study, we synthesized Mn-Bi nanopowders (NPs) using an in-house developed low-oxygen induction thermal plasma (LO-ITP) system [2]. The post-annealed Mn-Bi NPs were subsequently coated with a magnetically soft Fe layer via magnetron sputtering to form core-shell structured nanocomposite magnets. By meticulously optimizing the MnBi particle size, Fe coating layer thickness, and post-annealing conditions, the nanocomposite MnBi/Fe powders exhibited enhanced magnetization compared to their uncoated counterparts, demonstrating a promising approach to improve their magnetic performance for advanced applications.
The Mn-Bi NPs were initially synthesized via the LO-ITP process and subsequently post-annealed at 330 °C for 5 h to induce the desired low-temperature phase. The Fe layer was deposited at room temperature using magnetron sputtering. To prevent surface oxidation, all experiments and evaluations were conducted in a glovebox with oxygen level < 0.5 ppm).
The post-annealed MnBi powders without the Fe coating layer exhibited a coercivity of approximately 10.5 kOe and a saturation (remanent) magnetization of approximately 54.8 (35.2) emu/g. Upon coating the MnBi powders with an 80 nm thick Fe layer, the saturation magnetization increased to 62.5 emu/g. However, a slight decrease in coercivity to 8.5 kOe and remanent magnetization to 31.2 emu/g was observed. The positive ΔM value in the Henkel plot indicates the establishment of ferromagnetic exchange coupling at the interface between the hard and soft phases in the MnBi/Fe binary system. These findings confirm the successful fabrication of the core-shell structure, wherein the magnetically soft Fe layer effectively enhances the magnetic properties of the MnBi-based nanocomposite magnets. For further optimization, we also systematically optimize the MnBi/Fe thickness ratio by varying the MnBi powder size to further improve the magnetic properties of the MnBi/Fe composite magnets which will be discussed in detail in the presentation.
Acknowledgement: This study was supported by JSPS KAKENHI Grant Number 24K08105.
References: [1] J. Cui et. al., Acta Mater. 158, 118 (2018). [2] Hirayama, Y et al., J. Alloys Compd., 768, 608, (2018).
In this study, we synthesized Mn-Bi nanopowders (NPs) using an in-house developed low-oxygen induction thermal plasma (LO-ITP) system [2]. The post-annealed Mn-Bi NPs were subsequently coated with a magnetically soft Fe layer via magnetron sputtering to form core-shell structured nanocomposite magnets. By meticulously optimizing the MnBi particle size, Fe coating layer thickness, and post-annealing conditions, the nanocomposite MnBi/Fe powders exhibited enhanced magnetization compared to their uncoated counterparts, demonstrating a promising approach to improve their magnetic performance for advanced applications.
The Mn-Bi NPs were initially synthesized via the LO-ITP process and subsequently post-annealed at 330 °C for 5 h to induce the desired low-temperature phase. The Fe layer was deposited at room temperature using magnetron sputtering. To prevent surface oxidation, all experiments and evaluations were conducted in a glovebox with oxygen level < 0.5 ppm).
The post-annealed MnBi powders without the Fe coating layer exhibited a coercivity of approximately 10.5 kOe and a saturation (remanent) magnetization of approximately 54.8 (35.2) emu/g. Upon coating the MnBi powders with an 80 nm thick Fe layer, the saturation magnetization increased to 62.5 emu/g. However, a slight decrease in coercivity to 8.5 kOe and remanent magnetization to 31.2 emu/g was observed. The positive ΔM value in the Henkel plot indicates the establishment of ferromagnetic exchange coupling at the interface between the hard and soft phases in the MnBi/Fe binary system. These findings confirm the successful fabrication of the core-shell structure, wherein the magnetically soft Fe layer effectively enhances the magnetic properties of the MnBi-based nanocomposite magnets. For further optimization, we also systematically optimize the MnBi/Fe thickness ratio by varying the MnBi powder size to further improve the magnetic properties of the MnBi/Fe composite magnets which will be discussed in detail in the presentation.
Acknowledgement: This study was supported by JSPS KAKENHI Grant Number 24K08105.
References: [1] J. Cui et. al., Acta Mater. 158, 118 (2018). [2] Hirayama, Y et al., J. Alloys Compd., 768, 608, (2018).