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The Effect of Interfaces on Magnetisation Reversal in MnAl-C
Permanent magnets are key elements of modern society. Important application areas are energy conversion including eco-efficient transport, hydro- and wind power. A promising magnetic material is MnAl-C. Although it contains no ferromagnetic elements such as iron, nickel or cobalt, the so-called tau-MnAl-C is ferromagnetic up to high temperatures and has all properties which are prerequisites for high performance permanent magnets. The tau-MnAl-C contains no critical elements and therefore the long term use of this material is environmentally sustainable, in stark contrast to that of rare earth magnets such as Nd-Fe-B. In addition, tau-MnAl-C has a low physical density, which is a significant advantage for transport and aerospace applications.
In this project, a novel approach combining state of the art characterisation techniques with cutting edge computer simulations will be used to obtain quantitative information concerning the effect of interfaces on magnetisation reversal in tau-MnAl-C.

The first kick-off meeting took place in Dresden on 15 February 2018. Participants were Dr. Thomas G. Woodcock and Panpan Zhao from IFW Dresden, and Dr. Markus Gusenbauer and Dr. Thomas Schrefl from the Danube University Krems. The day was used extremely productively with status reports from the respective project partners, laboratory tour of the Institute for Metallic Materials, brainstorming to achieve the project goals and a detailed division of work for the coming project months.
An abstract was submitted to the Joint European Magnetic Symposia (JEMS) 2018 Conference, which will take place from September 3 - 7, 2018 in Mainz

„Automated micromagnetic simulations from native EBSD data"
Photo: Markus Gusenbauer

„Automated micromagnetic simulations from native EBSD data"
Micromagnetic simulations require a detailed knowledge of the crystallographic structure of the material. In permanent magnets with reduced or no rare-earth elements typically crystallographic eatures play an important role for the energy density product. In MnAl compounds twinning and antiphase boundaries are known to effect nucleation and pinning fields. Micromagnetic simulations can help to improve the understanding of these effects on the hysteresis properties.
In preliminary studies artificial microstructures have been used for the simulations. Here we take native Electron Backscatter Diffraction (EBSD) data of MnAl microstructures to automatically create high quality finite element meshes with adaptive mesh size. A fast micromagnetic solver, minimizing the Gibbs’ free energy, is applied subsequently and computes the hysteresis properties of the microscopic data.
The automated meshing and micromagnetic simulation routine is controlled via a Python script. Dream3D extracts EBSD data and converts them to a pixelated bitmap. Using image manipulation tools, the bitmap is automatically smoothed, corrected and upscaled. Iso2Mesh creates a 3D finite element mesh. An additional airbox, which is required for the stray field computation, is prepared with the Salome tool. The computed coercive fields are in the range of 0.36 T/μ0 to 0.53 T/μ0 depending on the density of defects.”
Unsere Projektpartner in Dresden haben einen Beitrag eingereicht beim Materials Science and Engineering Congress - MSE 2018, der vom 26. – 28. September in Darmstadt stattfinden wird (
“The Interaction of Twin Boundaries with Magnetic Domain Walls in MnAl-C Studied by Combined EBSD and Micromagnetic Modelling Techniques
The microstructure of MnAl-C is characterized by the presence of three different twin-like defects (pseudo twins, order twins, and true twins). Combined EBSD characterization and micromagnetic modelling has shown that the twin boundaries interact with magnetic domain walls and thus influence the magnetic properties of the material. This interaction is of great interest as the measured magnetic properties of MnAl-C are currently insufficient for the application of the material as a permanent magnet. Until now, only the twin boundary misorientation has been considered; however, a further two macroscopic degrees of freedom, giving the crystallographic orientation of the boundary plane, are required for a full description of the boundary. Various EBSD-based methods to obtain these two parameters for large numbers of boundaries are being explored in order to make the connection between the magnetic properties and the distribution of the twin boundary plane normal for the first time. Based on the results of microstructural characterization, finite element micromagnetic models are applied to investigate the interaction of domain walls and twin-like defect boundary. Through the simulation, the critical nucleation and depinning fields across these three crystallographically different twin-like defect boundaries are calculated, as well as the macroscopic magnetization profile.”



@ Details:
Thomas G. Woodcock,
IFW Dresden, Institute for Metallic Materials

FWF, Project: I 3288-N36

Photo: Markus Gusenbauer
Photo: Markus Gusenbauer