Metastable structures of pure and Fe-doped cobalt nitrides for rare-earth free magnets
Materials synthesis under far-from equilibrium conditions has become an important route for materials design and discovery which can drive systems toward metastable configurations which could possess otherwise unattainable functionality. Through crystal structure searches using adaptive genetic algorithm, we have explored metastable structures of binary and Fe-substituted cobalt nitrides for possible candidates for rare-earth free permanent magnets. New structures of ConN (n = 3…8) are found to have lower energies than those previously discovered by experiments. Some structures exhibit large magnetic anisotropy energy, reaching as high as 200 μeV per Co atom (or 2.45 MJ/m3) based on first-principles density functional calculation as shown in the figure. Substituting a fraction of Co with Fe helps to stabilize the new structures and at the same time further improve the magnetic properties. Our theoretical predictions provide useful insights into a promising system for discovery of new rare-earth free magnets and useful guideline for our experimental partner at University of Nebraska-Lincoln to work on this system.