Stability and magnetic properties of cobalt nitrides

• Ferromagnetic Co4+xN and Co3N1+y (0 < y < 0.5) were successfully synthesized.
• Co4+xN becomes a mixture of hexagonal Co3N1+y and cubic Co4+xN for N content > 20 at%.
• DFT calculations indicate for cubic/hexagonal phases the stoichiometry Co16N/CoN1.25.
• Co3N1+y magnetic behavior is strongly dependent on y, becoming AFM for y = 0.5.

Magnetic cobalt nitrides were synthesized via nitriding of cobalt particles under NH3 flux by a multi-step process that includes annealing at two temperatures: 823 K and 623 K. The phases Co4+xN and Co3N1+y were produced and their structure and magnetic properties were studied. Both phases are found to be ferromagnetic with saturation magnetization of 143 A m2 kg−1 and 33 A m2 kg−1 respectively and decompose above 650 K, before attaining the Curie temperature. Self-consistent Density Functional Theory (DFT) calculations were performed to understand the nitrides structure and magnetic behavior dependence on stoichiometry. The results indicate that the magnetic behavior of the hexagonal nitride is strongly dependent on the nitrogen content. The comparison of the experimental lattice parameters and magnetization values with the DFT calculations allows to determine the stoichiometry of the prepared compounds.