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Article

Microstructures and Magnetic Properties of Rare-Earth-Free Co-Zr-Mo-B Alloys

by
Tetsuji Saito
1,* and
Masaru Itakura
2
1
Department of Advanced Materials Science and Engineering, Chiba Institute of Technology, 2-17-1 Tsudanuma, Narashino 275-8588, Chiba, Japan
2
Department of Advanced Materials Science and Engineering, Faculty of Engineering Sciences, Kyushu University, Kasuga-shi 816-8580, Fukuoka, Japan
*
Author to whom correspondence should be addressed.
Crystals 2025, 15(8), 698; https://doi.org/10.3390/cryst15080698
Submission received: 21 June 2025 / Revised: 26 July 2025 / Accepted: 28 July 2025 / Published: 31 July 2025
(This article belongs to the Special Issue Innovations in Magnetic Composites: Synthesis to Application)
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Abstract

The growing demand for rare-earth magnets has raised concerns over their price and the country’s risk of depleting the supply of rare-earth elements. These severe concerns have led to the study of rare-earth-free magnets that do not rely on rare-earth elements. Co-Zr-Mo-B alloys, one of the prospective candidates for rare-earth-free magnets, were produced by the melt-spinning technique and subsequent annealing. It was found that a small substitution of Mo for Zr in the Co-Zr-B alloys increased coercivity. The Co-Zr-Mo-B alloy with a Mo content of 2 at% showed a high coercivity of 6.2 kOe with a remanence of 40 emu/g. SEM studies showed that the annealed Co-Zr-Mo-B alloys had fine, uniform grains with an average diameter of about 0.6 μm. Further studies using STEM demonstrated that the ferromagnetic phase in the annealed Co-Zr-Mo-B alloys with high coercivity was composed of the Co5Zr phase and the long-period stacking ordered (LPSO) phase. That is, the fine grains observed in the SEM studies were found to be ferromagnetic dendrites containing numerous twin boundaries of the Co5Zr phase and its derived LPSO phase. Therefore, the high coercivity of the Co-Zr-Mo-B alloys can be attributed to the presence of ferromagnetic crystals of Co5Zr and the derived LPSO phase.

1. Introduction

Recent developments in new permanent magnet materials have mainly been concentrated on rare-earth-containing alloys [1,2,3,4,5,6]. The maximum energy products of Nd-Fe-B rare-earth magnets have been improved to the extent of reaching their practical limitations [7,8,9]. The growing demand for the high-performance Nd-Fe-B rare-earth magnets has raised concerns over their price and the country risk of rare earth elements. These severe concerns have led to the study of rare-earth-free magnets that do not rely on rare-earth elements.
Several candidates for new rare-earth-free magnets have been identified, including the L10-FeNi and α′-Fe16N2 phases [10,11]. Since these phases exhibit high saturation magnetization, they are considered highly promising. However, they have not yet been developed into high-performance permanent magnets due to the difficulty of their synthesis. Recently, the L10-FeNi powder with a coercivity of 1.7 kOe has been successfully produced by the NITE (nitrogen insertion and topotactic extraction) method. The α″-Fe16N2 powder with a coercivity of 2.6 kOe has been obtained by chemical synthesis, that is, the reduction of nano-sized α-Fe2O3 powders followed by nitriding the resulting fine α-Fe powders. However, the current problem with these magnets is the difficulty of their synthesis [12,13].
The other candidate for new permanent magnetic materials is Co-Zr alloys [14]. It has been reported that the coercivity of the Co-Zr melt-spun ribbons was higher than that of the L10-FeNi and α″-Fe16N2 phases. As a consequence of intensive studies of Co-Zr system alloys, it has been determined that the Co11Zr2 phase, more appropriately expressed as the Co5Zr phase, is the origin of the hard magnetic properties of these alloys [15,16,17,18,19,20,21,22]. Although numerous attempts have been made to improve the magnetic properties of Co-Zr-B alloys, the magnetic properties are not yet comparable with those of rare-earth containing alloys [23,24,25,26,27,28,29,30,31,32,33,34,35]. Further work is, therefore, necessary to improve the magnetic properties of Co-Zr system alloys.
It has been reported that the addition of Mo or Nb into Co-Zr alloys increases the coercivity [20,21]. However, it is not clear why the addition of Mo or Nb into Co-Zr alloys leads to an increase in the coercivity. Thus, their structures and magnetic properties need to be systematically studied to improve the magnetic properties of Co-Zr system alloys further. In this study, Co-Zr-Mo-B alloys were produced by the melt-spinning technique and subsequent annealing. Microstructural and magnetic studies of the annealed alloys were carried out to determine the origin of the hard magnetic properties of the Co-Zr-Mo-B alloys.

2. Materials and Methods

2.1. Melt-Spinning

Melt-spun ribbons of Co80Zr18−xMoxB2 (x = 0–3) alloy were prepared in an argon atmosphere using a single-roller melt-spinning apparatus (NEV-A01, Nissin Giken, Osaka, Japan). First, the Co80Zr18−xMoxB2 (x = 0–3) alloy ingots were prepared by arc-melting Co lumps (99.9%, Kojundo Chemical Laboratory, Nerima, Japan), Zr ingots, Mo wires (99.95%, Nilaco, Chuo-ku, Japan), and B grains (99.5%, Kojundo Chemical Laboratory) in an argon atmosphere by an arc melting apparatus (NEV-AD03, Nissin Giken). The Zr ingots were prepared by arc-melting Zr sponge (99.6%, Hiranoseizaemon, Nara, Japan) before the preparation of the alloy ingots. The weight percent of the constituent elements of the Co80Zr18−xMoxB2 (x = 0–3) melt-spun ribbons is shown in Table 1. The alloy ingots were induction-melted in an argon atmosphere and then ejected through the orifice under argon pressure onto a copper wheel rotating at a surface velocity of 40 m/s. The fragmented melt-spun ribbons were wrapped in tantalum foil and then annealed in an argon atmosphere using an electric furnace (GFA430VN, Thermo Riko, Mitaka, Japan). The annealing of the Co80Zr18−xMoxB2 (x = 0–3) melt-spun ribbons was carried out at temperatures between 673 K and 1073 K for 1 h. After the annealing, the specimens were cooled to room temperature in the furnace under an argon atmosphere.

2.2. Characterization

The phases in the specimens were identified by X-ray diffraction (XRD) using Cu Kα radiation (MiniFlex600, Rigaku, Tokyo, Japan). The microstructures of the specimens were examined using a scanning electron microscope (SEM: ULTAR55, Carl Zeiss, Oberkochen, Germany) and a scanning transmission electron microscope (STEM: JEM-ARM200F, JEOL, Akishima, Japan) equipped with an energy-dispersive X-ray spectroscopy (EDS) system. The thermomagnetic properties of the specimens were measured in an argon atmosphere at a heating rate of 0.16 K/s using a differential thermal analysis (DTA: STA7300, Hitachi-Hightech, Minato-ku, Japan). The hysteresis loops of the specimens were measured at room temperature using a vibrating sample magnetometer (VSM: BHV-525RSCM, Riken Denshi, Japan) under a maximum applied field of 25 kOe. Since the applied magnetic field of the VSM was 25 kOe, the specimens had been magnetized in a pulsed magnetic field of 50 kOe prior to the VSM measurements.

3. Results and Discussion

3.1. Structures and Magnetic Properties

Figure 1 shows the XRD patterns of the Co-Zr-Mo-B melt-spun ribbons. The diffraction peaks of the Co5Zr and Co23Zr6 phases are found in the XRD patterns of the Co80Zr18B2 alloy. This indicates that the Co-Zr-Mo-B alloys consist of the Co5Zr and Co23Zr6 phases. In the Co-Zr system alloys, only the hard magnetic phase is the Co5Zr phase. The other phase, such as the Co23Zr6 phase, is the soft magnetic phase. Thus, the hard magnetic properties of the Co-Zr-based magnets are mainly dependent on the size of the Co5Zr phase. The Co80Zr18B2 melt-spun ribbon showed a coercivity of 2.7 kOe. The small addition of Mo to the Co-Zr-B alloys increased the coercivity. The highest coercivity of 3.5 kOe was achieved in the Co80Zr16Mo2B2 melt-spun ribbon. The resultant hysteresis loop is shown in Figure 2. As seen in the figure, the hysteresis loop is not smooth and has a somewhat constrained shape. This is because the specimen was an as-rapidly quenched melt-spun ribbon. Annealing of rapidly quenched melt-spun ribbons may result in a change in their structures and magnetic properties.
It is known that melt-spun ribbons with fine grains exhibit high coercivity in hard magnetic materials. Such fine grains are usually produced by annealing of rapidly quenched melt-spun ribbons. Thus, annealing of the Co-Zr-Mo-B melt-spun ribbons was performed. The magnetic properties of the Co-Zr-Mo-B melt-spun ribbons were successfully improved by annealing the rapidly solidified ribbons. The magnetic properties of the Co-Zr-Mo-B melt-spun ribbons were successfully improved by annealing the rapidly solidified ribbons. Figure 3 shows their coercivity. Regardless of the Mo content, the coercivity of the melt-spun ribbon increases to a peak value at 873 K and then gradually decreases as the annealing temperature increases. This is due to the grain growth of the Co5Zr phase. Thus, the structures and magnetic properties of the Co-Zr-Mo-B melt-spun ribbon annealed at 873 K were examined to determine the hard magnetic phase.
Figure 4 shows the XRD patterns of the annealed Co-Zr-Mo-B melt-spun ribbons. The corresponding thermomagnetic curves are shown in Figure 5. When annealed at 873 K, the ribbons consisted of the Co5Zr and Co23Zr6 phases. As the Mo content of the Co-Zr-Mo-B alloy increases, the diffraction peaks of the Co23Zr6 phase become less pronounced. This suggests that the small substitution of Mo for Zr in the Co80Zr18B2 alloy increases the formation of the Co5Zr phase. The thermomagnetic curve of the specimen exhibits a single magnetic transition near 740 K, corresponding to the Curie temperature of the Co5Zr phase. Virtually the same thermomagnetic curves are obtained from the Co-Zr-Mo-B alloys. This suggests that the added Mo is dissolved into the Co5Zr phase. The evidence of Mo dissolution into Co5Zr phase will be shown later. It is known that the Curie temperature of the Co23Zr6 phase is around 453 K [22,23]. However, no clear magnetic transition of the Co23Zr6 phase is found in the thermomagnetic curve. This indicates that the amount of Co23Zr6 phase in the alloys is quite limited. This leads to the conclusion that the hard magnetic phase in the Co-Zr-Mo-B alloys is the Co5Zr phase.
Figure 6 shows the remanence and coercivity of the annealed Co-Zr-Mo-B melt-spun ribbons. The hysterisis loop of the annealed Co80Zr16Mo2B2 melt-spun ribbon is shown in Figure 7. The annealed Co80Zr16Mo2B2 alloy exhibits a smooth hysteresis loop with a high coercivity of 6.2 kOe. The small substitution of Mo for Zr in the Co80Zr18B2 alloy did not result in an increase in the remanence value, but in an increase in the coercivity value.

3.2. Microstructures

The microstructures of the annealed Co80Zr18B2 and Co80Zr16Mo2B2 alloys were compared. Figure 8 shows SEM micrographs of these alloys. The average grain size and grain size distribution were estimated from the SEM micrographs. Fine grains are observed in the SEM micrograph of the annealed Co80Zr18B2 alloy. A similar SEM micrograph is obtained from the annealed Co80Zr16Mo2B2 alloy. Although the average grain size of these specimens is almost the same (approximately 0.6 μm), the grain size distribution of the Co80Zr16Mo2B2 alloy is smaller than that of the Co80Zr18B2 alloy. This suggests that the small substitution of Mo for Zr in the Co80Zr18B2 alloy is highly effective in obtaining fine, uniform grains. It is believed that such fine uniform grains in the annealed Co80Zr16Mo2B2 alloy give rise to the observed high coercivity. Figure 8 shows SEM secondary electron (SE) images reflecting the surface morphology of typical textures in these alloys. A similar SEM micrograph is obtained from the annealed Co80Zr16Mo2B2 alloy. Although the average grain size of these specimens is almost the same (approximately 0.6 μm), the grain size distribution of the Co80Zr16Mo2B2 alloy is smaller than that of the Co80Zr18B2 alloy. This suggests that the small substitution of Mo for Zr in the Co80Zr18B2 alloy is highly effective in obtaining fine, uniform grains. It is believed that such fine uniform grains in the annealed Co80Zr16Mo2B2 alloy give rise to the observed high coercivity. The inset in Figure 8b is a backscattered electron (BSE) image reflecting the composition obtained from the same microstructure, showing the dark contrast at the grain boundaries, i.e., the formation of fine particles made of lighter elements.
Detailed microstructural studies were performed by STEM. The STEM studies revealed that the fine grains about 0.6 μm observed in the SEM micrographs correspond to a dendritic texture consisting of a mixture of Co5Zr phase and a long-period stacking order (LPSO) phase derived from the Co5Zr phase. Figure 9 shows the transmission electron diffraction (TED) patterns obtained from the annealed Co80Zr18B2 and Co80Zr16Mo2B2 alloys. Debye rings, a series of diffraction spots from microcrystalline grains with various crystal orientations, are observed, indicating that both alloys have an isotropic microstructure. The rings with high intensity almost correspond to the lattice spacing of the Co5Zr phase, and the others are diffraction spots from Co23Zr6 and pure Co phases, but they are weaker in intensity and less abundant than those from the Co5Zr phase. In addition, diffraction spots are observed at positions that are integer multiples of the {111} spacing of the Co5Zr phase, suggesting that LPSO phases derived from the Co5Zr phase have formed. Comparing these two TED patterns, the diffraction spots of the Co5Zr phase from the Co80Zr16Mo2B2 alloy are clearer than those from the Co80Zr18B2 alloy, indicating that the addition of Mo improves the crystallinity. Furthermore, the intensity of diffraction spots from the Co23Zr6 phase is weaker in the Co80Zr16Mo2B2 alloy, indicating that the addition of Mo further suppresses the formation of the Co23Zr6 phase. Since the Co23Zr6 phase is a soft magnetic phase, the addition of Mo not only improves the crystallinity of the ferromagnetic phase but also suppresses the Co23Zr6 phase, thereby contributing to the increase in coercivity.
Figure 10 shows the STEM micrographs and corresponding STEM-EDS elemental mapping images of the dendritic texture of the annealed Co80Zr16Mo2B2 alloy. The EDS mapping shows that Zr and Mo are detected in almost the same area, and Mo uniformly substitutes for the Zr sites of the dendritic ferromagnetic phase. This suggests that the uniform distribution of Mo in the ferromagnetic phase changes the electronic state and results in high coercivity.
Figure 11 shows an atomic resolution STEM-HAADF image obtained from a part of the dendritic texture in the annealed Co80Zr16Mo2B2 alloy. The atomic HAADF image reflects the Z-contrast, and the lower right region matches well with the [ 1 1 ¯ 0 ] projection of the crystal structure of Co5Zr phase (Be5Au-type structure, F 4 ¯ 3 m ). In contrast, in the upper left region, the atomic positions are slightly displaced from the Be5Au-type structure, and the LPSO phase consisting of a superlattice with twice the lattice size of the Co5Zr phase in the 111 direction is formed. As is clear from Figure 11, the atomic arrangement changes continuously from the Co5Zr phase to the LPSO phase because the fundamental crystal structure is almost the same. In other words, the Co5Zr phase and its derived LPSO phase coexist to form the dendritic texture, and the volume fraction of the LPSO phase is relatively large. It was also found that the LPSO phase grows in a dendritic shape while forming many twin boundaries, just like the Co5Zr phase. A detailed microstructural analysis of the LPSO phase will be reported in a separate paper.
A microstructural model summarizing the SEM and STEM observations is shown in Figure 12. Note that in the SEM compositional image (inset in Figure 8b), only fine Co particles at the grain boundaries are observed because (Co5Zr + LPSO) and Co23Zr6 have similar average atomic numbers and cannot be distinguished. Both the annealed Co80Zr18B2 and Co80Zr16Mo2B2 alloys have a microstructure in which ferromagnetic crystals with dendritic structures of about 0.6 μm are surrounded by fine Co23Zr6 and pure Co particles, and it was found that the ferromagnetic crystals are composed of a Co5Zr phase with a Be5Au-type structure and an LPSO phase derived from it. It was also revealed that the addition of Mo improves the crystallinity by replacing the Zr sites of the Co5Zr phase and the LPSO phase with Mo, resulting in high coercivity.

4. Conclusions

A small substitution of Mo for Zr in Co-Zr-B alloys increased coercivity. From the microstructural studies, the role of the Mo additive was found to be a sharpening of the grain size distribution in the Co5Zr phase, more appropriately expressed as the Co5(Zr,Mo) phase. The resultant Co80Zr16Mo2B2 alloy showed a high coercivity of 6.2 kOe with a remanence of 40 emu/g. Thus, the high coercivity of the Co-Zr-Mo-B alloy is attributable to the existence of the fine Co5(Zr,Mo) phase. It was found that the ferromagnetic crystals are composed of a Co5Zr phase with a Be5Au-type structure and an LPSO phase derived from it. Additionally, the addition of Mo improves the crystallinity by replacing the Zr sites in both the Co5Zr phase and the LPSO phase with Mo.
This work clearly represents the microstructure of the Co5Zr phase using STEM and finds that the Co5Zr phase has a Be5Au-type structure and an LPSO phase derived from it. Further microstructural studies are necessary to reveal the quantitative correlation between phase composition and coercivity of the specimens.

Author Contributions

T.S.: methodology, writing, formal analysis, original draft preparation; M.I.: investigation, formal analysis, original draft preparation. All authors have read and agreed to the published version of the manuscript.

Funding

New Energy and Industrial Technology Development Organization (NEDO).

Data Availability Statement

Data are contained within the article.

Acknowledgments

This work was made possible by grants for the Rare Metal Substitute Materials Development Project from the New Energy and Industrial Technology Development Organization (NEDO).

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Sagawa, M.; Fujimura, S.; Togawa, N.; Yamamoto, H.; Matsuura, Y. New material for permanent magnets on a base of Nd and Fe. J. Appl. Phys. 1984, 55, 2083–2087. [Google Scholar] [CrossRef]
  2. Croat, J.J.; Herbst, J.F.; Lee, R.W.; Pinkerton, F.E. Pr-Fe and Nd-Fe-based materials: A new class of high-performance permanent magnets. J. Appl. Phys. 1984, 55, 2078–2082. [Google Scholar] [CrossRef]
  3. Li, J.; Sepehri-Amin, H.; Sasaki, T.; Ohkubo, T.; Hono, K. Most frequently asked questions about the coercivity of Nd-Fe-B permanent magnets. Sci. Technol. Adv. Mate. 2021, 22, 386–403. [Google Scholar] [CrossRef]
  4. Islam, R.; Verob, K.; Borah, J.P. Historical overview and recent advances in permanent magnet materials. Mater. Today Commun. 2024, 41, 110538. [Google Scholar] [CrossRef]
  5. Huang, L.; Luo, J.M.; Wang, C.Y.; Chai, W.X.; Zhang, X.S.; Hou, Y.H.; Li, W.; Yu, X.; Zhong, C.C.; Mao, H.Y.; et al. Significantly improved magnetic properties and thermal stability for sintered Nd-Fe-B magnets via grain boundary diffusion of DyCo alloy. Intermetallics 2024, 165, 108158. [Google Scholar] [CrossRef]
  6. Hioki, K. Development of high-performance hot-deformed Neodymium–Iron–Boron magnets without heavy rare-earth elements. Materials 2023, 16, 6581. [Google Scholar] [CrossRef]
  7. Saito, T.; Fujita, M.; Kuji, T.; Fukuoka, K.; Syono, Y. The development of high performance Nd-Fe-Co-Ga-B die upset magnets. J. Appl. Phys. 1998, 83, 6390–6392. [Google Scholar] [CrossRef]
  8. Sepehri-Amin, H.; Liu, L.; Ohkubo, T.; Yano, M.; Shoji, T.; Kato, A.; Schrefl, T.; Hono, K. Microstructure and temperature-dependent coercivity of hot-deformed Nd–Fe–B magnets diffusion processed with Pr–Cu alloy. Acta Mater. 2015, 99, 297–306. [Google Scholar] [CrossRef]
  9. Kulesh, N.; Bolyachkin, A.; Dengina, E.; Tang, X.; Ohkubo, T.; Kajiwara, T.; Miyawaki, H.; Sepehri-Amin, H.; Hono, K. Coercivity limits in Nd-Fe-B hot-deformed magnets with ultrafine microstructure. Acta Mater. 2024, 276, 120159. [Google Scholar] [CrossRef]
  10. Kotsugi, M.; Mitsumata, C.; Maruyama, H.; Wakita, T.; Taniuchi, T.; Ono, K.; Suzuki, M.; Kawamura, N.; Ishimatsu, N.; Oshima, M.; et al. Novel magnetic domain structure in iron meteorite induced by the presence of L10-FeNi. Appl. Phys. Exp. 2010, 3, 013001. [Google Scholar] [CrossRef]
  11. Sugita, Y.; Mitsuoka, K.; Komuro, M.; Hoshiya, H.; Kozono, Y.; Hanazono, M. Giant magnetic moment and other magnetic properties of epitaxially grown Fe16N2 single-crystal films. J. Appl. Phys. 1991, 70, 5977–5982. [Google Scholar] [CrossRef]
  12. Goto, S.; Kura, H.; Watanabe, E.; Hayashi, Y.; Yanagihara, H.; Shimada, Y.; Mizuguchi, M.; Takanashi, K.; Kita, E. Synthesis of single-phase L10-FeNi magnet powder by nitrogen insertion and topotactic extraction. Sci. Rep. 2017, 7, 13216. [Google Scholar] [CrossRef]
  13. Ogawa, T.; Ogata, Y.; Gallage, R.; Kobayashi, N.; Hayashi, N.; Kusano, Y.; Yamamoto, S.; Kohara, K.; Doi, M.; Takano, M.; et al. Challenge to the synthesis of α″-Fe16N2 phase compound nanoparticle with high saturation magnetization for rare earth free new permanent magnetic material. Appl. Phys. Exp. 2013, 6, 073007. [Google Scholar] [CrossRef]
  14. Ghemawat, A.M.; Foldeaki, M.; Dunlap, R.A.; O’Handley, R.C. New microcrystalline hard magnets in a Co-Zr-B alloy system. IEEE Trans. Magn. 1989, 25, 3312–3314. [Google Scholar] [CrossRef]
  15. Stadelmaier, H.H.; Jang, T.S.; Henig, E.-T. What is responsible for the magnetic hardness in Co-Zr (-B) alloys? Mater. Lett. 1991, 12, 295–300. [Google Scholar] [CrossRef]
  16. Sakurai, M.; Wang, R.; Liao, T.; Zhang, C.; Sun, H.; Sun, Y.; Wang, H.; Zhao, X.; Wang, S.; Balasubramanian, B.; et al. Discovering rare-earth-free magnetic materials through the development of a database. Phys. Rev. Mater. 2020, 4, 114408. [Google Scholar] [CrossRef]
  17. Gabay, A.M.; Zhang, Y.; Hadjipanayis, G.C. Cobalt-rich magnetic phases in Zr-Co alloys. J. Magn. Magn. Mater. 2001, 236, 37–41. [Google Scholar] [CrossRef]
  18. Ivanova, G.V.; Shchegoleva, N.N.; Gabay, A.M. Crystal structure of Zr2Co11 hard magnetic compound. J. Alloys Compd. 2007, 432, 135–141. [Google Scholar] [CrossRef]
  19. Saito, T.; Itakura, M. Microstructures of Co-Zr-B alloys produced by melt-spinning technique. J. Alloys Compd. 2013, 572, 124–128. [Google Scholar] [CrossRef]
  20. Thanh, P.T.; Duong, N.V.; Lam, N.M.; Hung, L.T.; Hau, K.X.; Ngoc, N.H.; Yen, N.H.; Dan, N.H. Investigation of Structure and Magnetic Properties of Melt-Spun Co-Zr-(B, Al) Ribbons. J. Supercond. Nov. Magn. 2022, 35, 1397–1403. [Google Scholar] [CrossRef]
  21. Stroink, G.; Stadnik, Z.M.; Viau, G.; Dunlop, R.A. The influence of quenching rate on the magnetic properties of microcrystalline alloys Co80Zr20−xBx. J. Appl. Phys. 1990, 67, 4963–4965. [Google Scholar] [CrossRef]
  22. Ishikawa, T.; Ohmori, K. Hard magnetic phase in rapidly quenched Zr-Co-B alloys. IEEE Trans. Magn. 1990, 26, 1370–1372. [Google Scholar] [CrossRef]
  23. Saito, T. Magnetization process in Co-Zr-B permanent magnet materials. IEEE Trans. Magn. 2004, 40, 2919–2921. [Google Scholar] [CrossRef]
  24. Zhang, J.B.; Sun, Q.W.; Wang, W.Q.; Su, F. Effects of Mo additive on structure and magnetic properties of Co82Zr18 alloy. J. Alloys Compd. 2009, 474, 48–51. [Google Scholar] [CrossRef]
  25. Hou, Z.P.; Zhang, J.B.; Xu, S.F.; Wu, C.; Zhang, J.J.; Wang, K.; Wang, W.Q.; Du, X.; Su, F. Effects of Nb substitution for Zr on the phases, microstructure and magnetic properties of Co80Zr18−xNbxB2 melt-spun ribbons. J. Magn. Magn. Mater. 2012, 324, 2771–2775. [Google Scholar] [CrossRef]
  26. Bhardwaj, V.; Pal, S.P.; Rao, N.V.R.; Chatterjee, R. Structural and magnetic properties of [1 1 0] oriented Co5Zr hard magnetic thin films. Mater. Lett. 2020, 260, 126869. [Google Scholar] [CrossRef]
  27. Saito, T. High performance Co-Zr-B melt-spun ribbons. Appl. Phys. Lett. 2003, 82, 2305–2307. [Google Scholar] [CrossRef]
  28. Zhao, X.; Ke, L.Q.; Nguyen, M.C.; Wang, C.Z.; Ho, K.M. Structures and magnetic properties of Co-Zr-B magnets studied by first-principles calculation. J. Appl. Phys. 2015, 117, 243902. [Google Scholar] [CrossRef]
  29. Hou, Z.P.; Yang, C.L.; Xu, S.F.; Zhang, J.B.; Liu, D.; Su, F.; Wang, W.Q. Effects of W substitution on the magnetic properties, phase evolution and microstructure of rapidly quenched Co80Zr18B2 alloy. J. Magn. Magn. Mater. 2014, 324, 116–120. [Google Scholar] [CrossRef]
  30. Zhang, W.Y.; Li, X.Z.; Valloppilly, S.; Skomski, R.; Shield, J.E.; Sellmyer, D.J. Magnetism of rapidly quenched rhombohedral Zr2Co11-based nanocomposites. J. Phys. D Appl. Phys. 2013, 46, 135004. [Google Scholar] [CrossRef]
  31. Oraon, A.; Adhikary, T.; Tirugabathina, M.; Kumar, B.; Ghosh, S.; Aich, S. Microstructure and magnetic properties of Co82-(x+y)Zr13V5BxSiy melt-spun ribbons. J. Alloys Compd. 2023, 965, 171436. [Google Scholar] [CrossRef]
  32. Imtyaz, M.D.; Rama Rao, N.V.; Aravindha Babu, D.; Ramesh Chandra, B.; Pandian, S. Effect of Cu substitution on structural and hard magnetic properties of rapidly solidified Zr18Co82-xCux melt spun ribbons. J. Alloys Compd. 2017, 699, 657–661. [Google Scholar] [CrossRef]
  33. Christopher, N.; Anand, K.; Singh, N. Enhancement of hard magnetic properties in rapidly quenched Zr–Co–Fe–B ribbons through vacuum annealing. Solid State Commun. 2021, 323, 114118. [Google Scholar] [CrossRef]
  34. Yue, L.P.; Jin, Y.L.; Sellmyer, D.J. Effect of Boron Addition on Magnetic-Domain Structure of Rapidly Quenched Zr2Co11-Based Nanomaterials. MRS Adv. 2016, 34, 2379–2385. [Google Scholar] [CrossRef]
  35. Oraon, A.; Adhikary, T.; Das, G.P.; Ghosh, S.; Garg, A.; Raja, A.; Aich, S. Combined experimental and DFT studies of Co82Zr12V6-xBx melt-spun ribbons to investigate structure and magnetic properties. J. Magn. Magn. Mater. 2022, 547, 168940. [Google Scholar] [CrossRef]
Crystals 15 00698 g001
Figure 1. XRD patterns of the Co80Zr18−xMoxB2 (x = 0–3) melt-spun ribbons: (a) Co80Zr18B2 alloy, (b) Co80Zr17Mo1B2 alloy, (c) Co80Zr16Mo2B2 alloy, and (d) Co80Zr15Mo3B2 alloy.
Figure 1. XRD patterns of the Co80Zr18−xMoxB2 (x = 0–3) melt-spun ribbons: (a) Co80Zr18B2 alloy, (b) Co80Zr17Mo1B2 alloy, (c) Co80Zr16Mo2B2 alloy, and (d) Co80Zr15Mo3B2 alloy.
Crystals 15 00698 g001
Crystals 15 00698 g002
Figure 2. Hysteresis loop of the Co80Zr16Mo2B2 melt-spun ribbon.
Figure 2. Hysteresis loop of the Co80Zr16Mo2B2 melt-spun ribbon.
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Figure 3. Dependence of coercivity of the Co80Zr18−xMoxB2 (x = 0–3) melt-spun ribbons on the annealing temperature.
Figure 3. Dependence of coercivity of the Co80Zr18−xMoxB2 (x = 0–3) melt-spun ribbons on the annealing temperature.
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Crystals 15 00698 g004
Figure 4. XRD patterns of the Co80Zr18−xMoxB2 (x = 0–3) melt-spun ribbons annealed at 873 K: (a) Co80Zr18B2 alloy, (b) Co80Zr17Mo1B2 alloy, (c) Co80Zr16Mo2B2 alloy, and (d) Co80Zr15Mo3B2 alloy.
Figure 4. XRD patterns of the Co80Zr18−xMoxB2 (x = 0–3) melt-spun ribbons annealed at 873 K: (a) Co80Zr18B2 alloy, (b) Co80Zr17Mo1B2 alloy, (c) Co80Zr16Mo2B2 alloy, and (d) Co80Zr15Mo3B2 alloy.
Crystals 15 00698 g004
Crystals 15 00698 g005
Figure 5. Thermomagnetic curves of the Co80Zr18−xMoxB2 (x = 0–3) melt-spun ribbons annealed at 873 K for 1 h: (a) Co80Zr18B2 alloy, (b) Co80Zr17Mo1B2 alloy, (c) Co80Zr16Mo2B2 alloy, and (d) Co80Zr15Mo3B2 alloy.
Figure 5. Thermomagnetic curves of the Co80Zr18−xMoxB2 (x = 0–3) melt-spun ribbons annealed at 873 K for 1 h: (a) Co80Zr18B2 alloy, (b) Co80Zr17Mo1B2 alloy, (c) Co80Zr16Mo2B2 alloy, and (d) Co80Zr15Mo3B2 alloy.
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Crystals 15 00698 g006
Figure 6. Dependence of remanence and coercivity of Co-Zr-Mo-B melt-spun ribbons annealed at 873 K for 1 h on Mo content.
Figure 6. Dependence of remanence and coercivity of Co-Zr-Mo-B melt-spun ribbons annealed at 873 K for 1 h on Mo content.
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Crystals 15 00698 g007
Figure 7. Hysteresis loop of the Co80Zr16Mo2B2 melt-spun ribbon annealed at 873 K for 1 h.
Figure 7. Hysteresis loop of the Co80Zr16Mo2B2 melt-spun ribbon annealed at 873 K for 1 h.
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Crystals 15 00698 g008
Figure 8. SEM micrographs and the average grain size (Dave) and grain size distributions estimated from the SEM micrographs of the melt-spun ribbon annealed at 873 K for 1 h: (a) Co80Zr18B2 alloy and (b) Co80Zr16Mo2B2 alloy. The corresponding backscattered electron (BSE) image is also shown in the inset of (b).
Figure 8. SEM micrographs and the average grain size (Dave) and grain size distributions estimated from the SEM micrographs of the melt-spun ribbon annealed at 873 K for 1 h: (a) Co80Zr18B2 alloy and (b) Co80Zr16Mo2B2 alloy. The corresponding backscattered electron (BSE) image is also shown in the inset of (b).
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Crystals 15 00698 g009
Figure 9. Transmission electron diffraction patterns obtained from the annealed Co80Zr18B2 and Co80Zr16Mo2B2 alloys melt-spun ribbons annealed at 873 K for 1 h.
Figure 9. Transmission electron diffraction patterns obtained from the annealed Co80Zr18B2 and Co80Zr16Mo2B2 alloys melt-spun ribbons annealed at 873 K for 1 h.
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Crystals 15 00698 g010
Figure 10. STEM micrographs (bright field (BF) image (a), dark field (DF) image (b)) and the corresponding STEM-EDS elemental mapping images (c–e) obtained from the Co80Zr16Mo2B2 melt-spun ribbon annealed at 873 K for 1 h.
Figure 10. STEM micrographs (bright field (BF) image (a), dark field (DF) image (b)) and the corresponding STEM-EDS elemental mapping images (c–e) obtained from the Co80Zr16Mo2B2 melt-spun ribbon annealed at 873 K for 1 h.
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Crystals 15 00698 g011
Figure 11. Atomic resolution STEM high-angle annular dark-field (HAADF) micrograph of a part of the dendritic texture in the Co80Zr16Mo2B2 melt-spun ribbon annealed at 873 K for 1 h. The image shows the [ 1 1 ¯ 0 ] projections of the crystal structure models of the Co5Zr and the LPSO phases.
Figure 11. Atomic resolution STEM high-angle annular dark-field (HAADF) micrograph of a part of the dendritic texture in the Co80Zr16Mo2B2 melt-spun ribbon annealed at 873 K for 1 h. The image shows the [ 1 1 ¯ 0 ] projections of the crystal structure models of the Co5Zr and the LPSO phases.
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Crystals 15 00698 g012
Figure 12. Microstructure model summarizing the results of our STEM studies.
Figure 12. Microstructure model summarizing the results of our STEM studies.
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Table 1. Nominal compositions of the Co80Zr18−xMoxB2 (x = 0–3) melt-spun ribbons.
Table 1. Nominal compositions of the Co80Zr18−xMoxB2 (x = 0–3) melt-spun ribbons.
Nominal CompositionWeight Percent
CoZrMoB
Co80Zr18B273.92 (wt%)25.74 (wt%) 0.339 (wt%)
Co80Zr17Mo1B273.86 (wt%)24.30 (wt%)1.50 (wt%)0.339 (wt%)
Co80Zr16Mo2B273.81 (wt%)22.85 (wt%)3.00 (wt%)0.338 (wt%)
Co80Zr15Mo3B273.75 (wt%)24.41 (wt%)4.50 (wt%)0.338 (wt%)
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Saito, T.; Itakura, M. Microstructures and Magnetic Properties of Rare-Earth-Free Co-Zr-Mo-B Alloys. Crystals 2025, 15, 698. https://doi.org/10.3390/cryst15080698

AMA Style

Saito T, Itakura M. Microstructures and Magnetic Properties of Rare-Earth-Free Co-Zr-Mo-B Alloys. Crystals. 2025; 15(8):698. https://doi.org/10.3390/cryst15080698

Chicago/Turabian Style

Saito, Tetsuji, and Masaru Itakura. 2025. "Microstructures and Magnetic Properties of Rare-Earth-Free Co-Zr-Mo-B Alloys" Crystals 15, no. 8: 698. https://doi.org/10.3390/cryst15080698

APA Style

Saito, T., & Itakura, M. (2025). Microstructures and Magnetic Properties of Rare-Earth-Free Co-Zr-Mo-B Alloys. Crystals, 15(8), 698. https://doi.org/10.3390/cryst15080698

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