Journal of the Japan Institute of Metals and Materials
Online ISSN : 1880-6880
Print ISSN : 0021-4876
ISSN-L : 0021-4876
Search
Advanced search
OR
Browse
Search
Volume 76, Issue 1
Displaying 1-16 of 16 articles from this issue
Show all abstracts
    • |<
    • <
    • 1
    • >
    • >|
Special Issue on Recent Progresses of Materials Science of Rare Earth Permanent Magnet Materials and Their Perspectives
Microstructure and Coercivity of Nd-Fe-B Magnets
Overview
  • Microstructure-Coercivity Relationships of Nd-Fe-B Base Permanent Magnets
    K. Hono, T. Ohkubo, H. Sepehri-Amin
    Article type: Special Issue
    2012 Volume 76 Issue 1 Pages 2-11
    Published: 2012
    Released on J-STAGE: January 01, 2012
    DOIhttps://doi.org/10.2320/jinstmet.76.2
    JOURNAL FREE ACCESS
    Show abstractHide abstract
      In spite of the long research history of Nd-Fe-B magnets, the understanding of the microstructure-coercivity relationships is not sufficient because of the difficulty of high quality microscopy work due to the strong oxidation tendency of Nd-rich phases during microscopy specimen preparation processes. In this paper, we review recent investigations on the microstructure-coercivity relationships using scanning electron microscopy, high resolution transmission electron microscopy (HRTEM) and laser assisted three-dimensional atom probe (3DAP) and discuss how to enhance the coercivity of Nd-Fe-B anisotropic magnets without using Dy.
    View full abstract
    Download PDF (12164K)
  • Enhancement of Coercivity of Nd-Fe-B Sintered Magnets by Grain Size Reduction
    Yasuhiro Une, Masato Sagawa
    Article type: Special Issue
    2012 Volume 76 Issue 1 Pages 12-16
    Published: 2012
    Released on J-STAGE: January 01, 2012
    DOIhttps://doi.org/10.2320/jinstmet.76.12
    JOURNAL FREE ACCESS
    Show abstractHide abstract
      For the purpose of increasing the coercivity of the Nd-Fe-B sintered magnets without Dy substitution, we explored a possibility of enhancing the coercivity by grain size reduction of the sintered body by employing the starting powder with an ultimately small particle size. To produce Nd-Fe-B alloy powder with such a small particle size, and to handle it to produce sintered bodies without oxidation, we developed a special jet mill and a special process called pressless process (PLP). By utilizing these techniques, it has become feasible to produce Nd-Fe-B sintered magnets with a coercivity of 1.59 MA/m without Dy substitution which is compared with 0.87 MA/m for the commercially available Nd-Fe-B sintered magnets containing no Dy.
    View full abstract
    Download PDF (2062K)
  • Nano-Dimensional Analysis of High-Performance Nd-Fe-B-Based Magnetic Materials for Micro-Structural Control
    Masaru Itakura, Noriyuki Kuwano
    Article type: Special Issue
    2012 Volume 76 Issue 1 Pages 17-26
    Published: 2012
    Released on J-STAGE: January 01, 2012
    DOIhttps://doi.org/10.2320/jinstmet.76.17
    JOURNAL FREE ACCESS
    Show abstractHide abstract
      Changes in microstructure of Nd-Fe-B based magnetic materials were investigated with advanced electron microscopes to study the Tb diffusion treatment for high coercivity for sintered magnets and the hydrogenation-decomposition-desorption-recombination (HDDR) process for high anistropic magnet powders. In sintered magnets, it was found that morphology of a Nd-rich wetting-layer phase changes to be continuous in shape and uniform in thickness in association with diffusion of Tb. The formation of the continuous Nd-rich wetting-layer phase containing a small amount of Tb leads to an effective increase in coercivity. In the HDDR magnet powder, a recombined Nd2Fe14B phase is formed first as a rim phase on spherical NdH2 grains during the DR-process. Small grain size of NdH2 phase and large grain size of α-Fe matrix after the HD-process can produce small grains of highly aligned Nd2Fe14B that lead to high remanence and high coercivity. These results indicate that a nano-dimensional analysis is essentially important to develop the high-performance of magnetic materials.
    View full abstract
    Download PDF (9020K)
  • Effects of Crystal Anisotropy, Grain and Domain Sizes on Coercovity Mechanism of the Nd-Fe-B Sintered Magnets
    Kurima Kobayashi, Kimiko Urushibata, Yasuhiro Une, Masato Sagawa
    Article type: Special Issue
    2012 Volume 76 Issue 1 Pages 27-35
    Published: 2012
    Released on J-STAGE: January 01, 2012
    DOIhttps://doi.org/10.2320/jinstmet.76.27
    JOURNAL FREE ACCESS
    Show abstractHide abstract
      The Dy-free and Dy-substituted (0-100%) Nd-Fe-B sintered magnets based on the NEOMAX-50 type magnet were prepared, and the magnetic properties such as the saturation magnetizations, the coercivities and the magnetic anisotropy constants (K1, K2) were determined by the obtained data using an high field magnetometer. The domain structures, especially domain widths were measured using MOKE and SEM, and the sizes of magnetic interacted regions were calculated based on the resulted values. The coercivity of the magnets is subjected to, first: the magnetic anisotropy field, second: crystal grain sizes, third: size of group of crystal grains behaving as a cooperated region that reflects the magnetic interaction through the grain boundary (GB).
    View full abstract
    Download PDF (3020K)
  • Effects of Annealing on the Coercivity in Sintered Nd-Fe-B Magnets
    Takahiro Akiya, Hiroaki Kato, Yasuhiro Une, Masato Sagawa
    Article type: Special Issue
    2012 Volume 76 Issue 1 Pages 36-42
    Published: 2012
    Released on J-STAGE: January 01, 2012
    DOIhttps://doi.org/10.2320/jinstmet.76.36
    JOURNAL FREE ACCESS
    Show abstractHide abstract
      In order to understand the coercivity enhancement mechanism by annealing in sintered Nd-Fe-B magnets, we performed systematic annealing experiments. It was found that an addition of 0.13% of Cu not only enhance the coercivity but also ease the required cooling condition after annealing to obtain high coercivity. Using single successive annealing technique, we observed a 0.3 MA/m jump in coercivity at annealing temperature Ta=640℃ for Cu-free Nd-Fe-B magnets and at Ta=440-460℃ for Cu containing ones. We also observed sharp reduction of 0.15 MA/m in coercivity for Cu doped sintered Nd-Fe-B magnets at Ta=600℃. Furthermore, we confirmed a reversible behavior of coercivity at the annealing temperature range which is lower than the optimal annealing temperature. This implies that some kinds of reversible structural natures depending on the temperature are closely related to the coercivity of sintered Nd-Fe-B magnets.
    View full abstract
    Download PDF (971K)
  • Effect of Magnetostatic Interaction on Magnetization Reversal Process in Nd-Fe-B Magnets —Computer Simulation—
    Hirotoshi Fukunaga, Kazuo Kirino, Masaki Nakano, Takeshi Yanai
    Article type: Special Issue
    2012 Volume 76 Issue 1 Pages 43-47
    Published: 2012
    Released on J-STAGE: January 01, 2012
    DOIhttps://doi.org/10.2320/jinstmet.76.43
    JOURNAL FREE ACCESS
    Show abstractHide abstract
      Magnetization reversal process of Nd-Fe-B sintered magnets was simulated based on the micromagnetic theory under consideration of the magnetostatic interaction and the cooperative effect of many grains. Reversal of magnetization was nucleated from magnetically soft grains. Then, the reversed region grew in the direction of applied field, and spread into the whole magnet when the applied field exceeded a critical value. The coercivity was decreased significantly by the existence of a small amount of magnetically soft grains, and did not depend on their fraction. Nonmagnetic inclusions between Nd2Fe14B grains also initiated magnetization reversal and decreased the coercivity. These effects of magnetostatic interaction were especially significant for the magnets with well-aligned grain orientation, and limited the obtainable coercivity to approximately 0.7 of the anisotropy field even if the magnet was consisted of perfect grains segregated from each other.
    View full abstract
    Download PDF (3953K)
Magnetic Domains in Nd-Fe-B Magnets
Overview
  • Magnetic Domain Observation and Magnetization Process Analysis of Nd-Fe-B Sub-Micron Grain Sized Magnet with High-Resolution Kerr Microscope
    Masaaki Takezawa
    Article type: Special Issue
    2012 Volume 76 Issue 1 Pages 48-51
    Published: 2012
    Released on J-STAGE: January 01, 2012
    DOIhttps://doi.org/10.2320/jinstmet.76.48
    JOURNAL FREE ACCESS
    Show abstractHide abstract
      A Kerr microscope that uses ultraviolet (UV) light for high-resolution magnetic domain observation was built, and the domain structure and magnetization process of hydrogenation-disproportionation-desorption-recombination (HDDR) magnets were examined. The UV Kerr microscope can observe nanometer-sized domain patterns. The coercivity of the HDDR magnet depends on the area of magnetization reversal during a reversal process. Magnetization reversal in a few grains simultaneously occurs in a low-coercivity magnet, because the Nd-rich phase along the grain boundaries is absent. On the other hand, magnetization reversal in a grain independently occurs owing to an adequate Nd-rich phase along the grain boundaries in a high-coercivity magnet. It follows that the high coercivity of an HDDR magnet is due to domain wall pinning at the grain boundaries.
    View full abstract
    Download PDF (1447K)
  • Magnetic Domain Observation of Nd-Fe-B/Nd-Cu Thin Films Deposited on Si Substrate
    Toshiyuki Shima, Kohtaro Sato, Yuriko Mishina, Tomoyuki Ohtsuki, Hirok ...
    Article type: Special Issue
    2012 Volume 76 Issue 1 Pages 52-58
    Published: 2012
    Released on J-STAGE: January 01, 2012
    DOIhttps://doi.org/10.2320/jinstmet.76.52
    JOURNAL FREE ACCESS
    Show abstractHide abstract
      It is well known that Nd-Fe-B magnet shows high performance as permanent magnets. It has been applied for various products such as sensors, actuators, and the motors for hybrid and electric vehicles, because of its high magnetocrystalline anisotropy and high saturation magnetization. From environmental issues, further high performance permanent magnet is needed. However, the coercivity of Nd-Fe-B magnets has reached only about 20% of the theoretical values. In order to understand the magnetization process of Nd-Fe-B alloys, the control of the grain size and the grain boundary is of importance. In this work, Nd-Fe-B/Nd-Cu thin films and circular dot arrays with 2 μm in diameter have been prepared by using ultra high vacuum sputtering system, electron beam lithography and Ar ion etching system and their magnetic properties have been investigated. Remarkable difference of the magnetization process between the Nd-Fe-B thin films with and without Nd-Cu additional layer was observed.
    View full abstract
    Download PDF (4524K)
Thin Films of Nd-Fe-B Magnets
Overview
  • Preparation and Magnetic Properties of Thick Film Magnets
    Masaki Nakano, Takeshi Yanai, Fumitoshi Yamashita, Hirotoshi Fukunaga
    Article type: Special Issue
    2012 Volume 76 Issue 1 Pages 59-64
    Published: 2012
    Released on J-STAGE: January 01, 2012
    DOIhttps://doi.org/10.2320/jinstmet.76.59
    JOURNAL FREE ACCESS
    Show abstractHide abstract
      In this report, we have introduced three topics of thick film magnets. After reviewing the development of sputtering-fabricated anisotropic Nd-Fe-B thick film magnets together with the outstanding investigations on other thick film magnets prepared by several deposition methods, the latest experimental results on PLD-made isotropic Nd-Fe-B thick film magnets are also reviewed.
    View full abstract
    Download PDF (1748K)
  • Interfacial Microstructure of Nd2Fe14B/Nd-Rich and Coercivity in Nd-Fe-B Films
    Masashi Matsuura, Ryota Goto, Nobuki Tezuka, Satoshi Sugimoto
    Article type: Special Issue
    2012 Volume 76 Issue 1 Pages 65-71
    Published: 2012
    Released on J-STAGE: January 01, 2012
    DOIhttps://doi.org/10.2320/jinstmet.76.65
    JOURNAL FREE ACCESS
    Show abstractHide abstract
      This study provides the relationship between phase change of Nd-rich and microstructural changes of Nd2Fe14B/Nd-rich interface in Nd-Fe-B films with different coercivity values. In as-deposited Nd-Fe-B film, flat interface of Nd2Fe14B/dhcp Nd is mainly observed. After oxidation, oxidized region was observed at the surface of Nd2Fe14B phase, and Nd2Fe14B/fcc NdOx interface were observed. In the Nd-Fe-B film subsequently annealed at 350℃ after oxidation, the coercivity of which decreases to around 20% of the value of as-deposited film, and the hcp Nd2O3 phase exists dominantly at the surface of Nd2Fe14B phase. In addition, there are some damaged regions at the surface of Nd2Fe14B phase. On the contrary, both the metastable C-Nd2O3 and amorphous phases existed dominantly at the Nd2Fe14B/Nd-rich interface of the film annealed at 650℃. The coercivity of this film recovered to the same value of as-deposited film.
       These results indicate that the crystallization of hcp Nd2O3 phase include some damages to neighboring Nd2Fe14B phase decrease coercivity. During annealing at 550 to 650℃, Nd-rich liquid phase appears and modifies the surface of Nd2Fe14B, and the coercivity recovers. After cooling, this liquid phase seems to crystallize into a C-Nd2O3 or an amorphous phases at the surface of Nd2Fe14B phase. In other words, the C-Nd2O3 or amorphous phases can exist without decreasing coercivity.
    View full abstract
    Download PDF (3066K)
New Processes of Nd-Fe-B Magnets
Overview
  • High-Magnetic-Field Annealing and Coercivity in Sintered Nd-Fe-B Magnets
    Hiroaki Kato, Takahiro Akiya, Kohki Takahashi
    Article type: Special Issue
    2012 Volume 76 Issue 1 Pages 72-80
    Published: 2012
    Released on J-STAGE: January 01, 2012
    DOIhttps://doi.org/10.2320/jinstmet.76.72
    JOURNAL FREE ACCESS
    Show abstractHide abstract
      Results of a systematic study concerned with the high-magnetic-field effects on the coercivity in processing various series of sintered Nd-Fe-B magnets are given. Coercivity enhancement phenomenon was observed in several series of sintered Nd-Fe-B magnets with Cu additive after annealing under magnetic fields of 10~14 T. A strong correlation was suggested between the field annealing temperature at which maximum coercivity increase was observed and the anomaly temperature in differential scanning calorimetry experiments. We found a linear relation between the room temperature coercivity Hc of the sample annealed at Ta=500℃ under magnetic field Ha for a series of samples with different Dy contents, which can be expressed as Hc=Hc(0)+ α Ha, with Hc(0) being the value for the zero-field-annealed sample and α, the coercivity enhancement factor. Although very small, α has a positive finite value in samples with 0 mass% and 2 mass% Dy. Significant increase in α value was confirmed for samples with Dy content larger than 6 mass%. This suggests the effects of higher anisotropy in paramagnetic susceptibility of Nd-rich intergranular phase containing Dy. Also introduced is the preliminary results of the grain boundary diffusion process of sinterd Nd-Fe-B samples with surface Dy layer under strong gradient magnetic fields produced by the 18 T superconducting magnets.
    View full abstract
    Download PDF (3002K)
  • Current Situation and Perspectives of Anisotropic Nanocomposite Permanent Magnet
    Satoshi Hirosawa
    Article type: Special Issue
    2012 Volume 76 Issue 1 Pages 81-88
    Published: 2012
    Released on J-STAGE: January 01, 2012
    DOIhttps://doi.org/10.2320/jinstmet.76.81
    JOURNAL FREE ACCESS
    Show abstractHide abstract
      In this review, some of selected theoretical and experimental studies on anisotropic nanocomposite permanent magnets are discussed. In order to achieve a large energy product surpassing those of anisotropic sintered Nd-Fe-B magnets, magnetic anisotropy of Nd2Fe14B dose not seem to be sufficiently large whereas strategic consideration of natural resources requires usage of Fe-Nd-based hard magnetic phases. As a future direction of research, it is proposed that composite magnets may be pursued as a means of reducing rare earth contents in a rare earth magnets, as was successfully achieved in the case of isotropic nanocomposite permanent magnets based on the Nd-Fe-B system. To realize sizable coercivity in the anisotropic nanocomposite magnets, domain wall movement should be pinned by internal microstructure in the hard magnetic phase, which eventually leads to requirement of intrinsic pinning of very narrow domain walls in the hard magnetic phase with a large anisotropy constant.
    View full abstract
    Download PDF (2647K)
Applications of Nd-Fe-B Magnets
  • Development of Dy-Free Nd-Fe-B Anisotropic Bonded Magnet and Application to the Small Motors
    Chisato Mishima, Kenji Noguchi, Masao Yamazaki, Hiroshi Matsuoka, Hiro ...
    Article type: Special Issue
    2012 Volume 76 Issue 1 Pages 89-95
    Published: 2012
    Released on J-STAGE: January 01, 2012
    DOIhttps://doi.org/10.2320/jinstmet.76.89
    JOURNAL FREE ACCESS
    Show abstractHide abstract
      The authors have successfully developed a low-cost anisotropic Nd-Fe-B magnet powder with a high coercivity value of 1591 kAm−1 without any dysprosium additives by diffusion processing of Nd-Cu-Al element into anisotropic magnet powder produced by the d-HDDR (dynamic-hydrogenation, disproportionation, desorption and recombination) method. This enhancement mechanism is to isolate the magnetic coupling between the grains of Nd2Fe14B phase by a Nd rich grain boundary phase with Cu. By surface coating this anisotropic magnet powder, the long-term aging loss behavior under air at 150℃ is less than 5% after 1000 h. By using this new anisotropic bonded magnet (New-MAGFINE), small automotive motors with excellent thermal stability and low cost characteristics have become possible.
    View full abstract
    Download PDF (5048K)
Sm Based Magnets
Overview
  • Present and Future of Sm2Co17 Magnets
    Ken Ohashi
    Article type: Special Issue
    2012 Volume 76 Issue 1 Pages 96-106
    Published: 2012
    Released on J-STAGE: January 01, 2012
    DOIhttps://doi.org/10.2320/jinstmet.76.96
    JOURNAL FREE ACCESS
    Show abstractHide abstract
      Sm2Co17 magnets have high thermal resistivity and corrosion resistance with over 240 kJ/m3 of (BH)max, which are well balanced ones. But as NdFeB magnets are superior to both magnetic properties and costs, the Sm2Co17 magnets are used in severe circumstance such as automobile applications. The magnetic property of Sm2Co17 magnets are reviewed at first and its coercive force mechanism is discussed. As follow, some applications are introduced.
    View full abstract
    Download PDF (4218K)
  • Progress and Prospects of SmFeN Magnets
    Michiya Kume, Takahiro Tomimoto, Muneo Yamamoto, Kohei Ihara, Hideaki ...
    Article type: Special Issue
    2012 Volume 76 Issue 1 Pages 107-111
    Published: 2012
    Released on J-STAGE: January 01, 2012
    DOIhttps://doi.org/10.2320/jinstmet.76.107
    JOURNAL FREE ACCESS
    Show abstractHide abstract
      More than 20 years have passed since SmFeN was discovered. At that time, because of its huge anisotropy field and high Curie temperature, SmFeN was expected to become a next-generation permanent magnetic material. However, SmFeN has the drawback that it cannot be sintered. Although considerable research has been carried out, this problem has still not been overcome. Therefore, SmFeN magnets have less potential for mass commercialization than NdFeB magnets. We propose two methods that are expected to lead to the commercial use of SmFeN. One is to increase coercivity by controlling the shape of particles, consequently increasing heat resistance. The other is to form products with new magnetic patterns by examining the magnetic orientation process. Moreover, it is important to use all rare-earth elements efficiently. Thus, we consider that SmFeN should be reappraised as a magnetic material.
    View full abstract
    Download PDF (1954K)
    • |<
    • <
    • 1
    • >
    • >|
feedback
 Top