"Mn3AlN" is Really Mn4N

Abstract

We investigate the synthesis of antiperovskite "Mn₃AlN" using the published synthesis procedure, as well as several new reaction pathways. In each case, only a combination of antiperovskite Mn₄N and Mn₅Al₈ or precursors is obtained. The identity of the obtained antiperovskite phase is unambiguously determined to be Mn₄N via synchrotron powder X-ray diffraction (SPXRD), X-ray absorption spectroscopy (XAS), and magnetometry. The experimental results are further supported by thermochemical calculations informed by density functional theory (DFT), which find Mn₃AlN to be metastable versus decomposition into Mn and AlN. The DFT-based calculations also predict an antiferromagnetic ground state for Mn₃AlN. This directly contradicts the previously reported ferromagnetic behavior of "Mn₃AlN". Instead, the observed magnetic behavior is consistent with ferrimagnetic Mn₄N. We examine the data in the original publication and conclude that the compound reported to be Mn₃AlN is in fact Mn₄N.