Presentation Information
[O14-3]Grain Shape and crystal reconstruction prediction of magnetic
Nanoparticles
*Gino Hrkac1, Hao Zhang1, Sepheri Amin Hussein2 (1. University of Exeter (UK), 2. NIMS (Japan))
Keywords:
molecular dynamics,crystal symmetry,rare earth magnets
Magnetic materials have a long history of driving technological growth and societal progress1. In the modern world, three of the most important industries, Green-Energy, the Automotive Sector, and Magnetic Recording are reliant on the improvement of at least one of a magnetic materials fundamental properties coercivity, anisotropy, stability, etc. Historically, the greatest leaps in performance were caused by the discovery of new crystal structures. For example, the transition from Steel to Alnico and Alnico to Rare-Earth based magnetic materials2.
We have developed a model which uses crystal symmetries to predict grain growth and shape as a function of size - measured in total atoms. The methodology we have developed is applicable to any crystal structure, especilly the probable shapes of Rare-Earth Intermetallics, particularly RT12 phases, whose stability, and therefore manufacturability, is dependent on its grains surrounding microstructure.
Our initial results on the test case of FePt L10 are supported by Magnetron-sputtering-based gas-phase condensation experiments, by Qui and Wang, that show FePt L10 has a strong preference for the Octahedron, and Truncated-Octahedron Minor shapes, verifying our model and methodology.
Our method allows experimentalists and modellers to produce quantitative data on the physical reasoning behind the texturing process. Take, for example, the well known fact that as-annealed FePt L10 thin films form hill like structures with {111} surface planes. Within our model it is possible to build various types of thin film structure and show quantitatively, within a Molecular Dynamics paradigm, why these hill like structures are energetically preferable. Further, for structures that aren’t as well studied as FePt L10, our model will be able to guide experimentalists by making predictions about preferred formations before an experiment has taken place.
To demonstrate the importance of surface type, we calculated the surface energy for each of the grains across the size range. Figure 1 shows these energies, normalised by the minimum surface energy at every size. As can be seen, the preference order we outlined above is reflected in the surface energies. For grains of identical composition, surface energy is the singular defining factor and for grains of this size range, surface type is the dominant factor affecting surface energy.
We have developed a model which uses crystal symmetries to predict grain growth and shape as a function of size - measured in total atoms. The methodology we have developed is applicable to any crystal structure, especilly the probable shapes of Rare-Earth Intermetallics, particularly RT12 phases, whose stability, and therefore manufacturability, is dependent on its grains surrounding microstructure.
Our initial results on the test case of FePt L10 are supported by Magnetron-sputtering-based gas-phase condensation experiments, by Qui and Wang, that show FePt L10 has a strong preference for the Octahedron, and Truncated-Octahedron Minor shapes, verifying our model and methodology.
Our method allows experimentalists and modellers to produce quantitative data on the physical reasoning behind the texturing process. Take, for example, the well known fact that as-annealed FePt L10 thin films form hill like structures with {111} surface planes. Within our model it is possible to build various types of thin film structure and show quantitatively, within a Molecular Dynamics paradigm, why these hill like structures are energetically preferable. Further, for structures that aren’t as well studied as FePt L10, our model will be able to guide experimentalists by making predictions about preferred formations before an experiment has taken place.
To demonstrate the importance of surface type, we calculated the surface energy for each of the grains across the size range. Figure 1 shows these energies, normalised by the minimum surface energy at every size. As can be seen, the preference order we outlined above is reflected in the surface energies. For grains of identical composition, surface energy is the singular defining factor and for grains of this size range, surface type is the dominant factor affecting surface energy.
