| AVS 63rd International Symposium & Exhibition | |
| Actinides and Rare Earths Focus Topic | Wednesday Sessions |
| Session AC+MI-WeM |
| Session: | Magnetism, Complexity, and Superconductivity in the Actinides and Rare Earths (8:00-11:00 am)/Actinide and Rare Earth Theory (11:00 am-12:20 pm) |
| Presenter: | Alexander I. Landa, Lawrence Livermore National Laboratory |
| Authors: | A. Landa, Lawrence Livermore National Laboratory A. Söderlind, Lawrence Livermore National Laboratory E.A. Turchi, Lawrence Livermore National Laboratory |
| Correspondent: | Click to Email |
SmCo5 (in the hexagonal CaCu5–type structure) magnets exhibit enormous uniaxial magnetocrystalline anisotropy (K1 ~ 17.2 MJ/m3) substantially higher than for the Nd2Fe14B (Neomax) magnets (K1 ~ 4.9 MJ/m3), and SmCo5 magnets have almost twice higher Curie temperature (Tc ~ 1020 K) than Nd2Fe14B magnets (Tc ~ 588 K). However the world market of permanent magnets is currently dominated by Neomax magnets (~ 62 %), which possess the highest energy performance with a record energy product of 470 kJ/m3 that is twice as high as the energy product of SmCo5 magnets, of 231 kJ/m3. Although SmCo5 magnets are more suitable for high temperature applications than Neomax, due to their relatively low energy performance SmCo5 magnets occupy only ~ 3% of the world market. From a cost point of view, it would be beneficial to substitute Co atoms with Fe because Fe in the Earth’s crust is ~ 2000 times more abundant than Co and consequently much cheaper. In addition, Fe is a ferromagnetic metal with the largest magnetization at room temperature. However SmFe5 is unstable, and does not appear in the equilibrium Sm-Fe phase diagram. Our presentation show results of ab initio Density Functional Theory based on the Exact Muffin-tin Orbital (EMTO) method for the heat of formation of Sm(Co1-xFex)5 alloys doped with different metals (Me). The Coherent Potential Approximation (CPA) implemented in the ab initio EMTO method allows us to gradually substitute the Co atoms by Fe atoms on the Cu-types sites of the CaCu5–type structure. Previous neutron diffraction studies of Th(Co1-xFex)5 alloys show that the larger Fe atoms prefer to occupy the 3g-type sites whereas the smaller Co atoms prefer to occupy the 2c-type sites. EMTO-CPA calculations reveal very small region (x ≤ 0.05) of stability of Sm(Co1-xFex)5 alloys. The Full-Potential Linear Muffin-tin Orbital (FPLMTO) calculations for SmCo5 and SmFe5 end points of SmCo5-SmFe5 phase diagram give similar results to those given by the EMTO method. We calculate the heat of formation of the pseudo-binary SmFe3(Me1-xCox)2 alloys where Fe atoms occupy all the 3g-type sites and the occupation of the 2c-type sites gradually changes from pure Me (SmFe3Me2 compound) to pure Co (SmFe3Co2 compound) within the CPA. Our calculations show that SmFe3(Me1-xCox)2 alloys could remain stable until approximately half of Me atoms are substituted by Co atoms. This work performed under the auspices of the US DOE by LLNL under Contract DE-AC52-07NA27344. This research is supported by the Critical Materials Institute, an Energy Innovation Hub funded by the US Department of Energy, Office of Energy Efficiency and Renewable Energy, Advanced Manufacturing Office.