Structural evolution and magnetic properties of Mn N compounds

Nanocrystalline Mn, Mn ₄N and Mn ₂N _0.86 are prepared by homogenization and nitrogenation of as-milled Mn powders under different conditions. Due to uncompensated surface spins, nanocrystalline Mn exhibits weak ferromagnetism, Mn ₄N displays ferrimagnetism, while Mn ₂N _0.86 dominant antiferromagnetism. The structural evolution of Mn→Mn ₄N→Mn ₂N _0.86 is interpreted as N atoms being in different percentages of the octahedral interstices of different Mn arrangements. In terms of the distances between Mn atoms with different atomic configurations of Mn(N) compounds, we think that the large discrepancy between the second-nearest distances of Mn ₄N and Mn ₂N _0.86 leads to their different magnetism.