Research

14 pages, 3209 KiB

Open AccessArticle

Dependences of Magnetic Properties on the Grain Size and Hard/Soft Magnetic Phase Volume Ratio for Ce₂Fe₁₄B/α-Fe and Nd₂Fe₁₄B/α-Fe Nanocomposites

by Xiangyi Liu, Bang Zhou, Bin Yuan and Zhongwu Liu

Materials 2023, 16(15), 5260; https://0-doi-org.brum.beds.ac.uk/10.3390/ma16155260 - 26 Jul 2023

Cited by 1 | Viewed by 829

Abstract

The magnetic properties of magnetic nanocomposites consisting of hard and soft magnetic phases are dependent not only on the intrinsic properties but also on the grain structure and volume ratio of the two phases. In this study, we performed a systematic micromagnetic simulation [...] Read more.

The magnetic properties of magnetic nanocomposites consisting of hard and soft magnetic phases are dependent not only on the intrinsic properties but also on the grain structure and volume ratio of the two phases. In this study, we performed a systematic micromagnetic simulation on the magnetic properties of Ce₂Fe₁₄B/α-Fe and Nd₂Fe₁₄B/α-Fe nanocomposites. The volume fractions of the hard magnetic Nd₂Fe₁₄B or Ce₂Fe₁₄B phase were varied from 80% to 40%, and the grain sizes of the hard magnetic phase and the soft magnetic α-Fe phase were changed independently from 10 nm to 40 nm. The results show that when the grain size of both hard and soft phases is 10 nm and the volume fraction of the hard phase is 70%, the highest maximum magnetic energy product can be obtained in both Ce₂Fe₁₄B/α-Fe and Nd₂Fe₁₄B/α-Fe nanocomposites. The hard magnetic properties of Ce₂Fe₁₄B/α-Fe nanocomposite decrease significantly when the volume fraction of the α-Fe phase exceeds 30%. However, for the Nd₂Fe₁₄B/α-Fe system, this situation only occurs when the α-Fe volume fraction exceeds 40%. The reason for this is not only because of the low anisotropic field and the smaller exchange coupling length between the soft and hard magnetic phases, but also because of the lower saturation magnetization of the hard phase. The grain size has greater effects on the magnetic properties compared to the volume fraction of the hard magnetic phase. The main reason is that as the grain size increases, the remanence of the nanocomposite decreases sharply, which also leads to a rapid decrease in the maximum magnetic energy product. The simulation results on the effects of phase ratio and grain size have been verified by experiments on melt-spun Ce₂Fe₁₄B/α-Fe alloys with various compositions prepared by melt-spinning followed by annealing for various lengths of time. Due to the influence of demagnetization energy, the hard magnetic phase with high saturation magnetization is preferred for the preparation of high-performance nanocomposite magnets. Full article

(This article belongs to the Special Issue Structures and Magnetic Properties of Nanostructured Permanent Magnets)

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10 pages, 14614 KiB

Open AccessArticle

Local Phase Segregation Induced by Ion Milling in 2:17-Type Sm-Co Based Magnets

by Xin Song, Yao Liu, Wentao Jia, Jian Li, Xiaolian Liu, Lizhong Zhao, Tao Yuan and Tianyu Ma

Materials 2023, 16(12), 4378; https://0-doi-org.brum.beds.ac.uk/10.3390/ma16124378 - 14 Jun 2023

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Abstract

Transmission electron microscopy (TEM) is indispensable to reveal the cellular nanostructure of the 2:17-type Sm-Co based magnets which act as the first choice for high-temperature magnet-associated devices. However, structural deficiencies could be introduced into the TEM specimen during the ion milling process, which [...] Read more.

Transmission electron microscopy (TEM) is indispensable to reveal the cellular nanostructure of the 2:17-type Sm-Co based magnets which act as the first choice for high-temperature magnet-associated devices. However, structural deficiencies could be introduced into the TEM specimen during the ion milling process, which would provide misleading information to understand the microstructure–property relationship of such magnets. In this work, we performed a comparative investigation of the microstructure and microchemistry between two TEM specimens prepared under different ion milling conditions in a model commercial magnet Sm₁₃Gd₁₂Co₅₀Cu_8.5Fe₁₃Zr_3.5 (wt.%). It is found that additional low-energy ion milling will preferably damage the 1:5H cell boundaries, while having no influence on the 2:17R cell phase. The structure of cell boundary transforms from hexagonal into face-centered-cubic. In addition, the elemental distribution within the damaged cell boundaries becomes discontinuous, segregating into Sm/Gd-rich and Fe/Co/Cu-rich portions. Our study suggested that in order to reveal the true microstructure of the Sm-Co based magnets, the TEM specimen should be carefully prepared to avoid structural damage and artificial deficiencies. Full article

(This article belongs to the Special Issue Structures and Magnetic Properties of Nanostructured Permanent Magnets)

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10 pages, 23099 KiB

Open AccessArticle

Achievement of High Perpendicular Anisotropy and Modification of Heat Treatment Peeling in Micron-Thickness Nd-Fe-B Films Used for Magnetic MEMS

by Jingbin Huang, Zhanyong Wang, Shijie Liao, Fang Wang, Min Huang and Jian Zhang

Materials 2023, 16(11), 4071; https://0-doi-org.brum.beds.ac.uk/10.3390/ma16114071 - 30 May 2023

Cited by 1 | Viewed by 830

Abstract

Thick Nd-Fe-B permanent magnetic films with good perpendicular anisotropy have important applications in magnetic microelectromechanical systems (MEMSs). However, when the thickness of the Nd-Fe-B film reaches the micron level, the magnetic anisotropy and texture of NdFeB film will become worse, and it is [...] Read more.

Thick Nd-Fe-B permanent magnetic films with good perpendicular anisotropy have important applications in magnetic microelectromechanical systems (MEMSs). However, when the thickness of the Nd-Fe-B film reaches the micron level, the magnetic anisotropy and texture of NdFeB film will become worse, and it is also prone to peeling during heat treatment, which seriously limits their applications. In this paper, Si(100)/Ta(100 nm)/Nd_xFe_91−xB₉(x = 14.5, 16.4, 18.2)/Ta (100 nm) films with thicknesses of 2–10 μm are prepared by magnetron sputtering. It is found that gradient annealing (GN) could help improve the magnetic anisotropy and texture of the micron-thickness film. When the Nd-Fe-B film thickness increases from 2 μm to 9 μm, its magnetic anisotropy and texture do not deteriorate. For the 9 μm Nd-Fe-B film, a high coercivity of 20.26 kOe and high magnetic anisotropy (remanence ratio M_r/M_s = 0.91) are achieved. An in-depth analysis of the elemental composition of the film along the thickness direction is conducted, and the presence of Nd aggregation layers at the interface between the Nd-Fe-B and the Ta layers is confirmed. The influence of thicknesses of the Ta buffer layer on the peeling of Nd-Fe-B micron-thickness films after high-temperature annealing is investigated, and it is found that increasing the thickness of the Ta buffer layer could effectively inhibit the peeling of Nd-Fe-B films. Our finding provides an effective way to modify the heat treatment peeling of Nd-Fe-B films. Our results are important for the development of Nd-Fe-B micron-scale films with high perpendicular anisotropy for applications in magnetic MEMS. Full article

(This article belongs to the Special Issue Structures and Magnetic Properties of Nanostructured Permanent Magnets)

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9 pages, 2725 KiB

Open AccessArticle

Microstructure Optimization and Coercivity Enhancement of Sintered NdFeB Magnet by Grain Boundary Diffusion of Multicomponent Tb₆₀Pr₁₀Cu₁₀Al₁₀Zn₁₀ Films

by Jingbin Huang, Min Huang, Fang Wang, Zhanyong Wang and Jian Zhang

Materials 2023, 16(8), 3131; https://0-doi-org.brum.beds.ac.uk/10.3390/ma16083131 - 16 Apr 2023

Viewed by 1462

Abstract

The use of magnetron sputtering film as a diffusion source was recently achieved in the industrial production of important grain-boundary-diffusion magnets. In this paper, the multicomponent diffusion source film is explored to optimize the microstructure of NdFeB magnets and improve their magnetic properties. [...] Read more.

The use of magnetron sputtering film as a diffusion source was recently achieved in the industrial production of important grain-boundary-diffusion magnets. In this paper, the multicomponent diffusion source film is explored to optimize the microstructure of NdFeB magnets and improve their magnetic properties. Multicomponent Tb₆₀Pr₁₀Cu₁₀Al₁₀Zn₁₀ films of 10 μm in thickness and single Tb films of 10 μm in thickness were deposited on commercial NdFeB magnets’ surfaces by magnetron sputtering as diffusion sources for grain boundary diffusion. The effects of diffusion on the microstructure and magnetic properties of the magnets were investigated. The coercivity of multicomponent diffusion magnets and single Tb diffusion magnets increased from 11.54 kOe to 18.89 kOe and 17.80 kOe, respectively. The microstructure and element distribution of diffusion magnets were characterized by scanning electron microscope and transmission electron microscopy. The multicomponent diffusion facilitates the infiltration of Tb along grain boundaries, rather than entering the main phase, thereby improving the Tb diffusion utilization. Furthermore, compared to the Tb diffusion magnet, the thicker thin-grain boundary was observed in multicomponent diffusion magnets. This thicker thin-grain boundary can effectively serve as the impetus for the magnetic exchange/coupling between grains. Therefore, the multicomponent diffusion magnets have higher coercivity and remanence. The multicomponent diffusion source has an increased mixing entropy and decreased Gibbs free energy, and it therefore does not easily enter the main phase but is retained in the grain boundary, thus optimizing the microstructure of the diffusion magnet. Our results show that the multicomponent diffusion source is an effective route for fabricating diffusion magnets with high performance. Full article

(This article belongs to the Special Issue Structures and Magnetic Properties of Nanostructured Permanent Magnets)

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12 pages, 3521 KiB

Open AccessArticle

Magnetic-Property Assessment on Dy–Nd–Fe–B Permanent Magnet by Thermodynamic Calculation and Micromagnetic Simulation

by Zhiming Dai, Kai Li, Zhenhua Wang, Wei Liu and Zhidong Zhang

Materials 2022, 15(21), 7648; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15217648 - 31 Oct 2022

Cited by 1 | Viewed by 1451

Abstract

Heavy rare-earth (HRE) elements are important for the preparation of high-coercivity permanent magnets. A further understanding of the thermodynamic properties of HRE phases, and the magnetization reversal mechanism of magnets are still critical issues to obtain magnets that can achieve better performance. In [...] Read more.

Heavy rare-earth (HRE) elements are important for the preparation of high-coercivity permanent magnets. A further understanding of the thermodynamic properties of HRE phases, and the magnetization reversal mechanism of magnets are still critical issues to obtain magnets that can achieve better performance. In this work, the Nd–Dy–Fe–B multicomponent system is investigated via the calculation of the phase diagram (CALPHAD) method and micromagnetic simulation. The phase composition of magnets with various ratios of Nd and Dy is assessed using critically optimized thermodynamic data. γ-Fe and Nd₂Fe₁₇ phases are suppressed when partial Nd is substituted with Dy (<9.3%), which, in turn, renders the formation of Nd₂Fe₁₄B phase favorable. The influence of the magnetic properties of grain boundaries (GBs) on magnetization reversal is detected by the micromagnetic simulations with the 3D polyhedral grains model. Coercivity was enhanced with both 3 nm nonmagnetic and the hard-magnetic GBs for the pinning effect besides the GBs. Moreover, the nucleation and propagation of reversed domains in core-shell grains are investigated, which suggests that the magnetic structure of grains can also influence the magnetization reversal of magnets. This study provides a theoretical route for a high-efficiency application of the Dy element, realizing a deterministic enhancement of the coercivity in Nd–Fe–B-based magnets. Full article

(This article belongs to the Special Issue Structures and Magnetic Properties of Nanostructured Permanent Magnets)

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10 pages, 1741 KiB

Open AccessArticle

The Effects of Forming CeFe₂ on Phase Structure and Magnetic Properties in Ce-Rich Nd-Ce-Fe-B Permanent Magnetic Materials

by Min Huang, Zhiqiang Qiu, Fang Wang, Hubin Luo, Changping Yang and Jian Zhang

Materials 2021, 14(20), 6070; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14206070 - 14 Oct 2021

Cited by 2 | Viewed by 1577

Abstract

The decomposition of the Nd-Ce-Fe-B phase to form CeFe₂ has been usually believed to have an important positive effect on the magnetic properties of Nd-Ce-Fe-B permanent magnetic materials. In this work, a new decomposition process of the Nd-Ce-Fe-B phase on the formation [...] Read more.

The decomposition of the Nd-Ce-Fe-B phase to form CeFe₂ has been usually believed to have an important positive effect on the magnetic properties of Nd-Ce-Fe-B permanent magnetic materials. In this work, a new decomposition process of the Nd-Ce-Fe-B phase on the formation of the CeFe₂ phase was observed to play a negative role in its magnetic properties. It is demonstrated that the Nd-Ce-Fe-B phase decomposes into non-magnetic CeFe₂, accompanied by the precipitation of Fe soft-phase. The kinks usually occurring in the demagnetization curves of Ce-rich Nd-Ce-Fe-B magnets have been determined to be related to the Fe soft-phase. Instead of using CeFe₂ as a grain-boundary phase, another Ce-Cu boundary phase has been explored to efficiently improve the coercivity of Ce-rich Nd-Ce-Fe-B magnets, provided that the Ce-Cu boundary phase has an appropriate Ce to Cu ratio. The present results contribute to the mechanism comprehension and high-performance design of Nd-Ce-Fe-B permanent magnetic materials. Full article

(This article belongs to the Special Issue Structures and Magnetic Properties of Nanostructured Permanent Magnets)

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12 pages, 6123 KiB

Open AccessArticle

Grain Boundary Evolution of Cellular Nanostructured Sm-Co Permanent Magnets

by Wei Zhang, Hongyu Chen, Xin Song and Tianyu Ma

Materials 2021, 14(18), 5179; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14185179 - 09 Sep 2021

Cited by 2 | Viewed by 1631

Abstract

Grain boundaries are thought to be the primary demagnetization sites of precipitate-hardening 2:17-type Sm-Co-Fe-Cu-Zr permanent magnets with a unique cellular nanostructure, leading to a poor squareness factor as well as a much lower than ideal energy product. In this work, we investigated the [...] Read more.

Grain boundaries are thought to be the primary demagnetization sites of precipitate-hardening 2:17-type Sm-Co-Fe-Cu-Zr permanent magnets with a unique cellular nanostructure, leading to a poor squareness factor as well as a much lower than ideal energy product. In this work, we investigated the grain boundary microstructure evolution of a model magnet Sm₂₅Co_46.9Fe_19.5Cu_5.6Zr_3.0 (wt. %) during the aging process. The transmission electron microscopy (TEM) investigations showed that the grain boundary region contains undecomposed 2:17H, partially ordered 2:17R, 1:5H nano-precipitates, and a Sm_n+1Co_5n−1 (n = 2, 1:3R; n = 3, 2:7R; n = 4, 5:19R) phase mixture at the solution-treated state. After short-term aging, further decomposition of 2:17H occurs, characterized by the gradual ordering of 2:17R, the precipitation of the 1:5H phase, and the gradual growth of Sm_n+1Co_5n−₁ compounds. Due to the lack of a defect-aggregated cell boundary near the grain boundary, the 1:5H precipitates are constrained between the 2:17R and the Sm_n+1Co_5n−1 nano-sheets. When further aging the magnet, the grain boundary 1:5H precipitates transform into Sm_n+1Co_5n−1 compounds. As the Sm_n+1Co_5n−1 compounds are magnetically softer than the 1:5H precipitates, the grain boundaries then act as the primary demagnetization sites. Our work adds important insights toward the understanding of the grain boundary effect of 2:17-type Sm-Co-Fe-Cu-Zr magnets. Full article

(This article belongs to the Special Issue Structures and Magnetic Properties of Nanostructured Permanent Magnets)

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12 pages, 4518 KiB

Open AccessArticle

Coercivity Mechanism and Magnetization Reversal in Anisotropic Ce-(Y)-Pr-Fe-B Films

by Jun Ma, Xiaotian Zhao, Wei Liu, Yang Li, Long Liu, Yuhang Song, Yuanhua Xie, Xinguo Zhao and Zhidong Zhang

Materials 2021, 14(16), 4680; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14164680 - 19 Aug 2021

Cited by 5 | Viewed by 1593

Abstract

In this study, the magnetic properties, coercivity mechanism, and magnetization reversal process were investigated for Ce-(Y)-Pr-Fe-B films. After the addition of Y and subsequent heating treatment, the formations of REO (RE ≡ Ce and Pr) and REFe₂ (RE ≡ rare earths) phases [...] Read more.

In this study, the magnetic properties, coercivity mechanism, and magnetization reversal process were investigated for Ce-(Y)-Pr-Fe-B films. After the addition of Y and subsequent heating treatment, the formations of REO (RE ≡ Ce and Pr) and REFe₂ (RE ≡ rare earths) phases are inhibited, and the microstructure of Ce-Y-Pr-Fe-B film is optimized. Meanwhile, the coercivity and the squareness of the hysteresis loop are significantly improved. The coercivity mechanism of Ce-Y-Pr-Fe-B film is determined to be a mixture of nucleation and pinning mechanisms, but dominated by the nucleation mechanism. The demagnetization results show that the nucleation of reversal magnetic domains leads to irreversible reversal. Our results are helpful to understand the coercivity mechanism and magnetization reversal of permanent magnetic films with multi-main phases. Full article

(This article belongs to the Special Issue Structures and Magnetic Properties of Nanostructured Permanent Magnets)

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