Vienna University of Technology, Institute of Solid State Physics, Wiedner Hauptstr. 8-10, 1040 Vienna, Austria.
Abstract:
The search for candidates of suitable magnetic materials, structures and their expected behaviour as reduction of the dysprosium/terbium content or the replacement for rare earth (RE) containing permanent magnets is of great economical and scientific interest. On the basis of density functional theory (DFT) calculations and numerical finite element micromagnetics we have analysed the limits of crystal anisotropy and shape anisotropy1,2 on the optimization of magnetization reversal processes in order to improve the coercive field of advanced hard magnets.
The microstructural model of the grains and intergranular phases which is used for theoretical simulations has been derived from a detailed nanoanalytical TEM/STEM study of Dy/Tb free magnets with different RE content and coercive field. Different types of grain boundaries are distinguished, such as the ones which are responsible for the nucleation processes of reversed domains and the ones acting as hindrance for reversed domain expansion. Special attention is laid on the EDX and EELS analysis of intergranular grain boundary phases with a thickness ranging from 3 - 5 nm.
We have performed first principle calculations using the Wien2k code3 which is based on the density functional theory in order to determine the magnetocrystalline anisotropy of RE2Fe14B with RE=Y, Pr, Nd, Dy, Tb. The aim is to obtain anisotropy values in dependence on the crystal lattice distortion and the substitution of rare earth atoms within the unit cell in order to understand the effect of the variation of crystal anisotropy and saturation polarization near grain boundaries4. Numerical finite element micromagnetic simulations based on the Landau-Lifshitz-Gilbert equation for magnetization reversal have been carried out in order to study the influence of internal demagnetizing fields determined by the microstructure on the magnetization switching behaviour.
The financial support from the European Community's Seventh Framework Programme (FP7-NMP) under grant agreement no. 280670 (REFREEPERMAG) and no: 309729 (ROMEO) is acknowledged.
References:
1. Toson, P; Wallisch, W; Asali, A; Fidler, J, Modelling of Packed Co Nanorods for Hard Magnetic Applications, EPJ Web of Conferences, 75 (2014) 03002, doi: 10.1051/epjconf/20147503002
2. Toson, P.; Asali, A.; Wallisch, W.; Zickler, G.; Fidler, J., "Nanostructured Hard Magnets: A Micromagnetic Study," Magnetics, IEEE Transactions on Magnetics, 51 (2015) 7400104, doi: 10.1109/TMAG.2014.2359093.
3. K. Schwarz, K; Blaha, P., “Solid state calculations using WIEN2k,” Comput. Mater. Sci., vol. 28, no. 2, pp. 259–273, 2003.
4. Asali, A.; Toson, P.; Blaha, P.; Fidler, J., "Dependence of Magnetic Anisotropy Energy on c/a Ratio of X2Fe14B (X = Y, Pr, Dy)," Magnetics, IEEE Transactions on Magnetics, 50 (2014) 7027504, doi: 10.1109/TMAG.2014.2326431.
The microstructural model of the grains and intergranular phases which is used for theoretical simulations has been derived from a detailed nanoanalytical TEM/STEM study of Dy/Tb free magnets with different RE content and coercive field. Different types of grain boundaries are distinguished, such as the ones which are responsible for the nucleation processes of reversed domains and the ones acting as hindrance for reversed domain expansion. Special attention is laid on the EDX and EELS analysis of intergranular grain boundary phases with a thickness ranging from 3 - 5 nm.
We have performed first principle calculations using the Wien2k code3 which is based on the density functional theory in order to determine the magnetocrystalline anisotropy of RE2Fe14B with RE=Y, Pr, Nd, Dy, Tb. The aim is to obtain anisotropy values in dependence on the crystal lattice distortion and the substitution of rare earth atoms within the unit cell in order to understand the effect of the variation of crystal anisotropy and saturation polarization near grain boundaries4. Numerical finite element micromagnetic simulations based on the Landau-Lifshitz-Gilbert equation for magnetization reversal have been carried out in order to study the influence of internal demagnetizing fields determined by the microstructure on the magnetization switching behaviour.
The financial support from the European Community's Seventh Framework Programme (FP7-NMP) under grant agreement no. 280670 (REFREEPERMAG) and no: 309729 (ROMEO) is acknowledged.
References:
1. Toson, P; Wallisch, W; Asali, A; Fidler, J, Modelling of Packed Co Nanorods for Hard Magnetic Applications, EPJ Web of Conferences, 75 (2014) 03002, doi: 10.1051/epjconf/20147503002
2. Toson, P.; Asali, A.; Wallisch, W.; Zickler, G.; Fidler, J., "Nanostructured Hard Magnets: A Micromagnetic Study," Magnetics, IEEE Transactions on Magnetics, 51 (2015) 7400104, doi: 10.1109/TMAG.2014.2359093.
3. K. Schwarz, K; Blaha, P., “Solid state calculations using WIEN2k,” Comput. Mater. Sci., vol. 28, no. 2, pp. 259–273, 2003.
4. Asali, A.; Toson, P.; Blaha, P.; Fidler, J., "Dependence of Magnetic Anisotropy Energy on c/a Ratio of X2Fe14B (X = Y, Pr, Dy)," Magnetics, IEEE Transactions on Magnetics, 50 (2014) 7027504, doi: 10.1109/TMAG.2014.2326431.