Special Issue "Manganese-based Permanent Magnets"


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

Deadline for manuscript submissions: closed (31 March 2014)

Special Issue Editor

Guest Editor
Prof. Dr. Ian Baker
Thayer School of Engineering, Dartmouth College, 8000 Cummings Hall, Hanover, NH 03755-8000, USA
Website: http://engineering.dartmouth.edu/people/faculty/ian-baker/
E-Mail: ian.baker@dartmouth.edu
Phone: +1 603 646 2184
Fax: +1 603 646 3856
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


Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. Papers will be published continuously (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

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

Published Papers (3 papers)

Metals 2014, 4(2), 130-140; doi:10.3390/met4020130 (doi registration under processing)
Received: 30 January 2014; in revised form: 3 April 2014 / Accepted: 4 April 2014 / Published: 17 April 2014
Show/Hide Abstract | Download PDF Full-text (846 KB) | View HTML Full-text | Download XML Full-text

Metals 2014, 4(1), 20-27; doi:10.3390/met4010020
Received: 18 December 2013; in revised form: 10 January 2014 / Accepted: 17 January 2014 / Published: 22 January 2014
Show/Hide Abstract | Download PDF Full-text (1085 KB) | View HTML Full-text | Download XML Full-text

Metals 2014, 4(1), 8-19; doi:10.3390/met4010008
Received: 13 December 2013; in revised form: 14 January 2014 / Accepted: 16 January 2014 / Published: 21 January 2014
Show/Hide Abstract | Download PDF Full-text (606 KB) | View HTML Full-text | Download XML Full-text

Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

Type of Paper: Article
Title: Options for Manganese-Based Alloys as Permanent Magnets
Author: Steve Constantinides
Affiliation: Arnold Magnetic Technologies Corp. 770 Linden Avenue, Rochester, NY 14625, USA
Binary and ternary alloys of the naturally ferromagnetic elements (iron, nickel and cobalt) have been exhaustively investigated for use as permanent magnets. A limited number of binary manganese alloys has also been investigated most notably MnAl and MnBi. An attempt to commercialize MnAl was made in 1979 by Matsushita. Shortly after the announcement of their product, neodymium iron boron was discovered and work on the manganese alloys ceased. With shortages and high prices of the rare earth elements, there is a renewed interest in Mn-based alloys. This work will review past investigation into Mn alloys for magnets and identify the potential for commercialization of the more promising alloys.

Type of Paper: Article
Microstructural Evolution in Mn-Al-Based Permanent Magnet Alloys
Jeffrey E. Shield, Michael Lucis and Yunlong Geng
Department of Mechanical & Materials Engineering and Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, NE, USA
Mn-Al-C-based permanent magnets based on the metastable L10 t phase possess relatively good magnetocrystalline anisotropy and saturation magnetization. To fully exploit the intrinsic magnetic properties, appropriate develop of micro/nanostructure is necessary. In this paper, we focus on the phase evolution and developing microstructure in Mn-Al-based alloys. For example, melt spinning proved to be an effective route to phase-pure e-MnAl, the parent of the ferromagnetic t-MnAl. The as-spun microstructural scale was on the order of hundreds of nanometers. Nanostructuring has been accomplished by both high energy mechanical milling and through alloying additions, resulting in grain sizes of tens of nanometers and coercivities approaching 5 kOe.

Type of Paper: Article
Microstructure and Magnetic Properties of Bulk Nanocrystalline MnAl
Anurag Chaturvedi, Rumana Yaqub and Ian Baker
Thayer School of Engineering, Dartmouth College, Hanover NH 03755, USA
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 t 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 ≤4.3 kOe and a saturation magnetization of ≤56 emu/g. In addition, extrusions exhibit greater than 95% of the theoretical density. This study opens a new window in the area of anisotropic magnets with improved magnetic properties for technological use.

Type of Paper: Article
Effect of Compositions and Heat Treatment on Magnetic Properties of MnBi
Jun Cui
Pacific Northwest National Laboratory, PO Box 999, Richland, WA 99352, USA
MnBi has the potential to replace some of the rare-earth based permanent magnetic material. The coercivity of MnBi increases with increasing temperature, making it a good candidate for high temperature application. MnBi itself has relatively low saturation magnetization, about 8 kG at room temperature and 7 kG at 200°C. It must be exchange coupled with soft phases such as FeCo or Co to attain higher magnetization and higher energy product. The first step toward MnBi based composite magnet is to obtain high quality hard phase in large quantity and in submicron sizes. However, MnBi is difficult to obtain in high purity, partly because the reaction between Mn and Bi is peritectic, and partly because Mn reacts readily with oxygen. In addition there is a eutectic reaction at 262°C, which causes MnBi to decompose during the bulk magnet fabrication process. Compositions and heat treatments have drastic effect to the phase contents and magnetic properties of the obtained MnBi material. In this paper, we report our effort on obtaining high performance MnBi hard phase through composition and heat treatment optimization. To date, high purity MnBi (>90%) can be routinely produced in large quantity. The optimum composition is Mn55.9Bi44.1. The heat treated powder exhibits 74 emu/g saturation magnetization at room temperature with 9 T applied field. After proper alignment, the energy product of the powder reached 11.9 MGOe, and that of the sintered bulk magnet reached 7.8 MGOe at room temperature.

Type of Paper: Article
Low-Energy Route to Fabrication of MnAl-Based Permanent Magnetic Materials
Laura Henderson Lewis
Department of Chemical Engineering, Northeastern University, Boston, MA 02115, USA; E-Mail: lhlewis@neu.edu
Nanostructured ribbons of a bulk Al45Mn55 alloy are fabricated by rapid solidification via melt-spinning. The ribbons are heat treated at moderate temperatures, and the thermal evolution of their magnetic and structural character is investigated. The as-solidified material exhibits a large exchange bias shift below a magnetic blocking temperature TB ~ 95 K (as much as 13 kOe at 10 K); the exchange bias is ascribed to exchange-coupling between ferromagnetic Mn-poor and antiferromagnetic Mn-rich regions in a majority hexagonal ε-MnAl phase. Upon heat treatment at Tanneal > 523 K (250 °C), the metastable tetragonal L10-type τ-MnAl phase, which is known to possess attractive hard ferromagnetic character, begins to nucleate at the expense of the parent ε-phase. The onset of the ε → τ transition occurs at a temperature 100 K less than previous reports.

Type of Paper: Article
Structure and Properties Revolutions for Hard Magnetic MnAl and MnGa Based Alloys Prepared by Melt Spinning or Mechanical Milling
Zhongwu Liu 1,*, Kunpeng Su 1,2 and Yitian Cheng 1
1 School of Materials Science and Engineering, South China University of Technology, Guangzhou, 510640, China; E-Mail: zwliu@scut.edu.cn
Institute of Materials Physics, Hangzhou Dianzi University, Hangzhou 310018, China
Mn based alloys such as MnAl, MnBi and MnGa are potential substitutions for rare earth permanent magnets with moderate magnetic properties. To make full use of these groups of materials, the effects of process on the structure and properties have to be well understood. In this work, the phase structure and magnetic properties of melt spun Mn55Al45 based alloys with C, B and RE doping and MnGa alloys with various compositions were investigated. As-spun Mn-Al, Mn-Al-C and Mn-Al-C-RE ribbons had single hexagonal ε phase structure. Phase transformations of ε→τ at about 500 °C and τ→ε at about 800 °C were verified when heating the samples to high temperatures. Moderate carbon addition can promote the formation of the desired hard magnetic L10 τ-phase and improve the magnetic properties. Mn53.3Al45C1.7 alloy annealed at 650 °C had saturation magnetization JS of 0.83 T, intrinsic coercivity of 123 kA/m and maximum energy product of 12.2 kJ/m3. The Curie temperature TC of τ phase is very sensitive to the C concentration, but doping Dy or Pr in MnAlC alloy had no significant effect on TC. Pr addition can slightly improve the magnetic properties of MnAlC alloy, especially JS. B is found to not beneficial to the stabilization of τ phase and to the magnetic properties of MnAl alloy. For MnGa alloys, Mn/Ga atomic ratio has important effect on the phase structure. Heat treatment can significantly enhance on the magnetic properties. High coercivity up to 480 kA/m can be obtained in the annealed ribbons. Efforts are dedicated to improve the magnetization of the alloys. In addition, [001] textured MnAlC flakes were fabricated by surfactant assisted ball milling (SABM). After SABM for 8 h the flakes had a thickness below 200 nm and an aspect ratio as high as 102–103. As-SABMed samples consist of single phase of hcp ε-phase. After annealed at suitable temperatures, both bulk and SABM powders can transform from ε to the metastable ferromagnetic τ-phase completely. The magnetic properties are strongly dependent on both the fraction of the τ-phase and the particle size. A high coercivity of ~242.8 kA/m and a saturation magnetization of about 0.49T have been achieved. The coercivity value for the milled powders exceeds the experimental value for the bulk materials by ~128.8%.
Mn-Al based alloys; Mn-Ga alloys; permanent magnet; melt spinning; surfactant assisted ball milling; magnetic properties

Last update: 23 January 2014

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