Computational discovery of permanent magnet materials

The first criteria for permanent magnetic material design is hexagonal and tetragonal structures which allow magnetic moments to align along the anisotropic crystal-axis. The non-equivalent crystal sites play a key role in determining the permanent magnet properties. Advanced density functional calculations incorporating electron-correlation and spin-orbit coupling show highest magnetic anisotropy contributed by R-1a (rare earth) site due to the crystal-field split 4f-states followed by the R centered T-2c (transition-element) ring sandwiched by T-3g in hexagonal RT₅. The split 4f-states and the formation of T-2c 3d and R-1a 5d density of states peaks at the Fermi level are the origins of the maximum anisotropy. Calculations indicate that Co sites can be substituted by Fe to enhance the magnetic moment in SmCo₅. Replacing Sm by Ce indeed shows c-axis anisotropy. Further engineering CeCo₅ with Cu substitution shows enhanced magnetic anisotropy without significant reduction in the magnetic moment. One third of Ce sites substitution in CeCo₅ by Co derives Ce₂Co₁₇ to hexagonal.