Designing rare earth free permanent magnets: insights from small Co clusters

With the ultimate goal of rational design of permanent magnets without rare earth elements, we study the magnetic properties of Co 4 clusters doped with six different group 14 and group 15 elements, using first principles electronic structure methods, based on density functional theory. For the first time, low energy isomers and magnetic moments of pure Co 4 and Co 6 clusters, and the doped clusters are identified through a global search employing an evolutionary algorithm. The magnetic anisotropy energy (MAE) of these clusters is then calculated. No correlation is found between the type of dopant atom and MAE. Through further analyses we establish that MAE is largely determined by the sum of absolute values of the spin moments on the individual atoms, and the HOMO-LUMO gap of the system. The importance of these in designing new permanent magnetic materials is discussed. With the ultimate goal of rational design of rare earth free permanent magnets, microscopic origins of large MAE in Co 4 clusters doped with group 14 and 15 elements are investigated using DFT.