Tag: Research

[PDF] “Grain-size dependent demagnetizing factors in permanent magnets” reprint update

The reprint of our Journal of Applied Physics (JAP) paper “Grain-size dependent demagnetizing factors in permanent magnets” has been updated since the old version was not being discovered by the Google Scholar crawler.

There is also now a version on arXiv. I hope that Google Scholar will now correctly index the paper so that it’s easier for people to find!

The full, correct reference for the paper is:

S. Bance, B. Seebacher, T. Schrefl, L. Exl, M. Winklhofer, G. Hrkac, G. Zimanyi, T. Shoji, M. Yano, N. Sakuma, M. Ito, A. Kato and A. Manabe, “Grain-size dependent demagnetizing factors in permanent magnets”, J. Appl. Phys. 116, 233903 (2014); http://dx.doi.org/10.1063/1.4904854

 




[Paper] Replacement and Original Magnet Engineering Options (ROMEOs): A European Seventh Framework Project to Develop Advanced Permanent Magnets Without, or with Reduced Use of, Critical Raw Materials

New paper

Figure from the paper.

Our latest paper has been published in JOM (Springer). It is a summary of the achievements (so far) of the ROMEO fp7 project.

ROMEO is a project that aims to research and develop novel microstructural-engineering strategies that will dramatically improve the properties of magnets based purely on light rare earth elements, especially the coercivity, which will enable them to be used for applications above 100 deg.

Abstract

The rare-earth crisis, which peaked in the summer of 2011 with the prices of both light and heavy rare earths soaring to unprecedented levels, brought about the widespread realization that the long-term availability and price stability of rare earths could not be guaranteed. This triggered a rapid response from manufacturers involved in rare earths, as well as governments and national and international funding agencies. In the case of rare-earth-containing permanent magnets, three possibilities were given quick and serious consideration: (I) increased recycling of devices containing rare earths; (II) the search for new, mineable, rare-earth resources beyond those in China; and (III) the development of high-energy-product permanent magnets with little or no rare-earth content used in their manufacture. The Replacement and Original Magnet Engineering Options (ROMEO) project addresses the latter challenge using a two-pronged approach. With its basis on work packages that include materials modeling and advanced characterization, the ROMEO project is an attempt to develop a new class of novel permanent magnets that are free of rare earths. Furthermore, the project aims to minimize rare-earth content, particularly heavy-rare-earth (HRE) content, as much as possible in Nd-Fe-B-type magnets. Success has been achieved on both fronts. In terms of new, rare-earth-free magnets, a Heusler alloy database of 236,945 compounds has been narrowed down to approximately 20 new compounds. Of these compounds, Co2MnTi is expected to be a ferromagnet with a high Curie temperature and a high magnetic moment. Regarding the reduction in the amount of rare earths, and more specifically HREs, major progress is seen in electrophoretic deposition as a method for accurately positioning the HRE on the surface prior to its diffusion into the microstructure. This locally increases the coercivity of the rather small Nd-Fe-B-type magnet, thereby substantially reducing the dependence on the HREs Dy and Tb, two of the most critical raw materials identified by the European Commission. Overall, the ROMEO project has demonstrated that rapid progress can be achieved when experts in a specific area are brought together to focus on a particular challenge. With more than half a year of the ROMEO project remaining, further progress and additional breakthroughs can be expected.

Reference

P. McGuiness, O. Akdogan, A. Asali, S. Bance, F. Bittner, J. M. D. Coey, N. M. Dempsey, J. Fidler, D. Givord, O. Gutfleisch, M. Katter, D. Le Roy, S. Sanvito, T. Schrefl, L. Schultz, C. Schwöbl, M. Soderžnik, S. Šturm, P. Tozman, K. Üstüner, M. Venkatesan, T. G. Woodcock, K. Žagar, S. Kobe, “Replacement and Original Magnet Engineering Options (ROMEO): A European 7th Framework project to develop advanced permanent magnets without, or with reduced use of, critical raw materials”, JOM (Springer), 24-4-2015, doi: 10.1007/s11837-015-1412-x




[Paper] “Thermal Activation in Permanent Magnets” published in JOM

Explanation of method for calculating the thermally activated coercivity of using micromagnetics.

Explanation of method for calculating the thermally activated coercivity of using micromagnetics.

This week our new paper titled “Thermal Activation in Permanent Magnets” has been published in JOM (Springer). The invited paper is under a special topic, “Permanent Magnets beyond Nd-Dy-Fe-B“.  An author manuscript (reprint) is available here.

In the paper we provide a more detailed overview of the micromagnetic methods we have developed to model the thermal activation of permanent magnets. These methods allow us to simulate and understand the behaviour of permanent magnets at finite temperatures, which is important since the generators in wind turbines and electric motors in green cars operate at higher temperatures. For example, in electric cars the typical operation temperature of the motors can be around 450ºK (177º C).

Using two examples from our work with Toyota and the ROMEO project we highlight the importance of reversal mechanisms in explaining the observed performance (for example, coercivity) of the magnets.

The paper is initially published “online first” here with the permanent DOI 10.1007/s11837-015-1415-7. It can be cited as follows:

S. Bance, J. Fischbacher, A. Kovacs, H. Oezelt, F. Reichel, T. Schrefl, “Thermal Activation in Permanent Magnets”, JOM  2015 DOI:10.1007/s11837-015-1415-7

Abstract

The coercive field of permanent magnets decays with temperature. At non-zero temperatures, the system can overcome a finite energy barrier through thermal fluctuations. Using finite element micromagnetic simulations, we quantify this effect, which reduces coercivity in addition to the decrease of the coercive field associated with the temperature dependence of the anisotropy field, and validate the method through comparison with existing experimental data.




“ROMEO” project featured on TV news

Our EU-funded FP7 project “Replacement and Original Magnet Engineering Options” (ROMEO) has recently been covered in the news in Slovenia, to promote the participation of our Slovenian collaborators.

News footage of the ROMEO project

Click for news footage of the ROMEO project >>>

There is also now a project newsletter highlighting the aims and progress of the project. Please click here to download it.

 




[Paper] “Thermally activated coercivity in core-shell permanent magnets” published in vol. 117 of Journal of Applied Physics.

Our new paper “Thermally activated coercivity in core-shell permanent magnets” has been published today as J. Appl. Phys. 117, 17A733 (2015); http://dx.doi.org/10.1063/1.4916542 . In the paper we use numerical miromagnetics to calculate the performance of nanostructured core-shell-like permanent magnets, like the type that can now be produced by grain boundary diffusion of granular hot-deformed or sintered rare earth permanent magnets.

Figure 3 - FIG. 3. Reversal processes in the sin- gle grain models with (i) a pure NdFeB grain, (ii) a NdFeB grain with a soft outer defect, and (iii) NdFeB core, (Dy, Nd)FeB shell and an outer soft defect. Thermally activated coercive field values are indicated with the field direction (red arrows). The saddle point image is the configuration with the highest total energy, forming the peak of the energy barrier.

FIG. 3. Reversal processes in the sin- gle grain models with (i) a pure NdFeB grain, (ii) a NdFeB grain with a soft outer defect, and (iii) NdFeB core, (Dy, Nd)FeB shell and an outer soft defect. Thermally activated coercive field values are indicated with the field direction (red arrows). The saddle point image is the configuration with the highest total energy, forming the peak of the energy barrier.

The paper is free online for 30 days, after which the pre/re-print version will still be available here.