event
Thursday 04 Oct 2012: FMG seminar: Influence of grain boundaries and ceramic/metallic interfaces on the coercivity of high performancecNd2Fe14B magnets
Professor Gino Hrkac (Exeter) - Engineering, CEMPS, University of Exeter
HAR/170 (3D Visualisation Suite) 14:00-15:00
Anisotropic sintered NdFeB magnets consist of polyhedral grains, which have a distribution of size and shape, separated by a grain boundary phase with various compositions. Such magnets are sensitive to the crystallographic structure near grain boundaries and interfaces, and this considerably influences the magnetization reversal behavior. The local arrangement of atoms next to the grain boundary also depends on the crystallographic orientation relationship between neighboring grains. Different grain boundary compositions result in a localized change of magnetic properties such as anisotropy. To understand the interaction of multiple grains in realistic sintered magnets and to quantify these changes we perform solid-state molecular dynamics and modified embedded atom calculations of various interfaces between the Nd-rich phase (metallic Nd and NdxOx) and the Nd2Fe14B phase, including doping materials, such as Co, Cu, ...
In the simulations we investigate the displacement of the atoms at boundary interfaces and compare them with experiments. Once the magnitudes of the displacements are quantified they are used as input parameters to calculate the local change in anisotropy. The values for the anisotropy are estimates based on magnetostriction data. In addition the simulations give the penetration depth of distortions of the intrinsic magnetic properties from their bulk values for different interface conditions.
We show that the combination of atomistic and micromagnetic simulations can give a better understanding of the morphological and chemical composition of grain boundaries and their effect on the magnetic properties on the coercivity of magnetic grains [1,2].
[1] G. Hrkac, T. Woodcock, et al, Applied Physics Letters 97, 2010, 232511
[2] T. Woodcock, Y. Zhang, G. Hrkac et al. Scripta Materialia, Volume 67, Issue 6, 2012, Pages 536–541
