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Metals
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Manganese-based Permanent Magnets
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Manganese-based Permanent Magnets

A special issue of Metals (ISSN 2075-4701).

Deadline for manuscript submissions: closed (31 March 2015) | Viewed by 46206

Special Issue Editor

Prof. Dr. Ian Baker

E-Mail Website
Guest Editor
Thayer School of Engineering, Dartmouth College, 14 Engineering Drive, Hanover, NH 03755-8000, USA
Interests: microstructural characterization; phase transformations; mechanical properties; magnetic materials

Special Issue Information

Dear Colleagues,

There is a significant gap between the energy product, BHmax, of both the traditional ferrite and AlNiCo permanent magnets of less than 10 MGOe and that of the rare earth magnets of greater than 30 MGOe. This is a gap that Mn-based magnets could potentially fill inexpensively. This special issue presents work on the development of both MnAl and MnBi permanent magnets. Some of the challenges involved in the development of these magnets include improving the compounds’ energy product, increasing the thermal stability of these metastable compounds, and producing them in quantity as a bulk material. These challenges are addressed from both experimental and theoretical points of view in the papers presented here.

Prof. Dr. Ian Baker
Guest Editors

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Keywords

  • permanent magnets
  • Mn-based magnets
  • maximum energy product
  • MnAl
  • MnBi

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Published Papers (6 papers)

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Editorial

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279 KiB  
Editorial
Manganese-based Permanent Magnets
by Ian Baker
Metals 2015, 5(3), 1435-1436; https://doi.org/10.3390/met5031435 - 11 Aug 2015
Cited by 2 | Viewed by 4071
Abstract
There is a significant gap between the energy product, BH, where B is the magnetic flux density and H is the magnetic field strength, of both the traditional ferrite and AlNiCo permanent magnets of less than 10 MGOe and that of the rare [...] Read more.
There is a significant gap between the energy product, BH, where B is the magnetic flux density and H is the magnetic field strength, of both the traditional ferrite and AlNiCo permanent magnets of less than 10 MGOe and that of the rare earth magnets of greater than 30 MGOe. This is a gap that Mn-based magnets could potentially, inexpensively, fill. This Special Issue presents work on the development of both types of manganese permanent magnets. Some of the challenges involved in the development of these magnets include improving the compounds’ energy product, increasing the thermal stability of these metastable compounds, and producing them in quantity as a bulk material.[...] Full article
(This article belongs to the Special Issue Manganese-based Permanent Magnets)

Research

Jump to: Editorial

824 KiB  
Article
Epitaxial Growth of Hard Ferrimagnetic Mn3Ge Film on Rhodium Buffer Layer
by Atsushi Sugihara, Kazuya Suzuki, Terunobu Miyazaki and Shigemi Mizukami
Metals 2015, 5(2), 910-919; https://doi.org/10.3390/met5020910 - 2 Jun 2015
Cited by 11 | Viewed by 6695
Abstract
Mn\(_3\)Ge has a tetragonal Heusler-like D0\(_{22}\) crystal structure, exhibiting a large uniaxial magnetic anisotropy and small saturation magnetization due to its ferrimagnetic spin structure; thus, it is a hard ferrimagnet. In this report, epitaxial growth of a Mn\(_3\)Ge film on a Rh buffer [...] Read more.
Mn\(_3\)Ge has a tetragonal Heusler-like D0\(_{22}\) crystal structure, exhibiting a large uniaxial magnetic anisotropy and small saturation magnetization due to its ferrimagnetic spin structure; thus, it is a hard ferrimagnet. In this report, epitaxial growth of a Mn\(_3\)Ge film on a Rh buffer layer was investigated for comparison with that of a film on a Cr buffer layer in terms of the lattice mismatch between Mn\(_3\)Ge and the buffer layer. The film grown on Rh had much better crystalline quality than that grown on Cr, which can be attributed to the small lattice mismatch. Epitaxial films of Mn\(_3\)Ge on Rh show somewhat small coercivity (\(H_{\rm c}\) = 12.6 kOe) and a large perpendicular magnetic anisotropy (\(K_{\rm u}\) = 11.6 Merg/cm\(^3\)), comparable to that of the film grown on Cr. Full article
(This article belongs to the Special Issue Manganese-based Permanent Magnets)
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1209 KiB  
Article
Electronic Structure and Maximum Energy Product of MnBi
by Jihoon Park, Yang-Ki Hong, Jaejin Lee, Woncheol Lee, Seong-Gon Kim and Chul-Jin Choi
Metals 2014, 4(3), 455-464; https://doi.org/10.3390/met4030455 - 29 Aug 2014
Cited by 63 | Viewed by 10239
Abstract
We have performed first-principles calculations to obtain magnetic moment, magnetocrystalline anisotropy energy (MAE), i.e., the magnetic crystalline anisotropy constant (K), and the Curie temperature (Tc) of low temperature phase (LTP) MnBi and also estimated the maximum energy [...] Read more.
We have performed first-principles calculations to obtain magnetic moment, magnetocrystalline anisotropy energy (MAE), i.e., the magnetic crystalline anisotropy constant (K), and the Curie temperature (Tc) of low temperature phase (LTP) MnBi and also estimated the maximum energy product (BH)max at elevated temperatures. The full-potential linearized augmented plane wave (FPLAPW) method, based on density functional theory (DFT) within the local spin density approximation (LSDA), was used to calculate the electronic structure of LPM MnBi. The Tc was calculated by the mean field theory. The calculated magnetic moment, MAE, and Tc are 3.63 μB/f.u. (formula unit) (79 emu/g or 714 emu/cm3), −0.163 meV/u.c. (or K = −0.275 × 106 J/m3) and 711 K, respectively. The (BH)max at the elevated temperatures was estimated by combining experimental coercivity (Hci) and the temperature dependence of magnetization (Ms(T)). The (BH)max is 17.7 MGOe at 300 K, which is in good agreement with the experimental result for directionally-solidified LTP MnBi (17 MGOe). In addition, a study of electron density maps and the lattice constant c/a ratio dependence of the magnetic moment suggested that doping of a third element into interstitial sites of LTP MnBi can increase the Ms. Full article
(This article belongs to the Special Issue Manganese-based Permanent Magnets)
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846 KiB  
Article
Phase Transitions in Mechanically Milled Mn-Al-C Permanent Magnets
by Michael J. Lucis, Timothy E. Prost, Xiujuan Jiang, Meiyu Wang and Jeffrey E. Shield
Metals 2014, 4(2), 130-140; https://doi.org/10.3390/met4020130 - 17 Apr 2014
Cited by 29 | Viewed by 7413
Abstract
Mn-Al powders were prepared by rapid solidification followed by high-energy mechanical milling. The rapid solidification resulted in single-phase ε. The milling was performed in both the ε phase and the τ phase, with the τ-phase formation accomplished through a heat treatment at 500 [...] Read more.
Mn-Al powders were prepared by rapid solidification followed by high-energy mechanical milling. The rapid solidification resulted in single-phase ε. The milling was performed in both the ε phase and the τ phase, with the τ-phase formation accomplished through a heat treatment at 500 °C for 10 min. For the ε-milled samples, the conversion of the ε to the τ phase was accomplished after milling via the same heat treatment. Mechanical milling induced a significant increase in coercivity in both cases, reaching 4.5 kOe and 4.1 kOe, respectively, followed by a decrease upon further milling. The increase in coercivity was the result of grain refinement induced by the high-energy mechanical milling. Additionally, in both cases a loss in magnetization was observed. Milling in the ε phase showed a smaller decrease in the magnetization due to a higher content of the τ phase. The loss in magnetization was attributed to a stress-induced transition to the equilibrium phases, as no site disorder or oxidation was observed. Surfactant-assisted milling in oleic acid also improved coercivity, but in this case values reached >4 kOe and remained stable at least through 32 h of milling. Full article
(This article belongs to the Special Issue Manganese-based Permanent Magnets)
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1085 KiB  
Article
Microstructure and Magnetic Properties of Bulk Nanocrystalline MnAl
by Anurag Chaturvedi, Rumana Yaqub and Ian Baker
Metals 2014, 4(1), 20-27; https://doi.org/10.3390/met4010020 - 22 Jan 2014
Cited by 50 | Viewed by 8358
Abstract
MnAl is a promising rare-earth free permanent magnet for technological use. We have examined the effects of consolidation by back-pressure, assisted equal channel angular extrusion processing on mechanically-milled, gas-atomized Mn-46% at. Al powder. X-ray diffraction showed both that the extruded rod consisted mostly [...] Read more.
MnAl is a promising rare-earth free permanent magnet for technological use. We have examined the effects of consolidation by back-pressure, assisted equal channel angular extrusion processing on mechanically-milled, gas-atomized Mn-46% at. Al powder. X-ray diffraction showed both that the extruded rod consisted mostly of metastable τ phase, with some of the equilibrium γ2 and β phases, and that it largely retained the as-milled nanostructure. Magnetic measurements show a coercivity of ≤4.4 kOe and a magnetization at 10 kOe of ≤40 emu/g. In addition, extrusions exhibit greater than 95% of the theoretical density. This study opens a new window in the area of bulk MnAl magnets with improved magnetic properties for technological use. Full article
(This article belongs to the Special Issue Manganese-based Permanent Magnets)
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606 KiB  
Article
Magnetism-Structure Correlations during the ε→τ Transformation in Rapidly-Solidified MnAl Nanostructured Alloys
by Felix Jiménez-Villacorta, Joshua L. Marion, John T. Oldham, Maria. Daniil, Matthew A. Willard and Laura H. Lewis
Metals 2014, 4(1), 8-19; https://doi.org/10.3390/met4010008 - 21 Jan 2014
Cited by 42 | Viewed by 8104
Abstract
Magnetic and structural aspects of the annealing-induced transformation of rapidly-solidified Mn55Al45 ribbons from the as-quenched metastable antiferromagnetic (AF) ε-phase to the target ferromagnetic (FM) L10 τ-phase are investigated. The as-solidified material exhibits a majority hexagonal ε-MnAl phase revealing [...] Read more.
Magnetic and structural aspects of the annealing-induced transformation of rapidly-solidified Mn55Al45 ribbons from the as-quenched metastable antiferromagnetic (AF) ε-phase to the target ferromagnetic (FM) L10 τ-phase are investigated. The as-solidified material exhibits a majority hexagonal ε-MnAl phase revealing a large exchange bias shift below a magnetic blocking temperature TB~95 K (Hex~13 kOe at 10 K), ascribed to the presence of compositional fluctuations in this antiferromagnetic phase. Heat treatment at a relatively low annealing temperature Tanneal ≈ 568 K (295 °C) promotes the nucleation of the metastable L10 τ-MnAl phase at the expense of the parent ε-phase, donating an increasingly hard ferromagnetic character. The onset of the ε→τ transformation occurs at a temperature that is ~100 K lower than that reported in the literature, highlighting the benefits of applying rapid solidification for synthesis of the rapidly-solidified parent alloy. Full article
(This article belongs to the Special Issue Manganese-based Permanent Magnets)
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