Experimental Confirmation of Predicted Cobalt-Based Magnetic Antiperovskite Nitrides

Nitrides of the form X₃AN (where X is a 3d metal Mn, Fe, Ni, Co) are subset of antiperovskite materials with exciting properties. Examples of magnetic antiperovskites include: Co₃FeN, which has been reported as half-metallic, Fe₃FeN (i.e., Fe₄N) and its N-vacancy ordered derivative Fe₁₆N₂, which is the strongest known ferromagnet, and Mn₃CuN, which exhibits a giant magnetostrictive effect. Recently, several Co-containing antiperovskites, including Co₃PdN and Co₃PtN were predicted to be stable, despite no experimental reports.
In this study, we investigate the synthesis, stability, and magnetic properties of cobalt-based thin films Co₃PdN, Co₃PtN, and Co₃ZnN, fabricated via magnetron sputtering. Our findings show that Co₃PdN and Co₃ZnN exhibit greater stability compared to Co₃PtN. Synchrotron X-ray diffraction data for stoichiometric Co₃PdN and Co₃ZnN reveal a cubic antiperovskite structure with lattice constants of 3.806 Å and 3.743 Å, respectively. Experimentally, Co₃PdN is identified as a soft magnetic material, with a low-temperature coercive field (H_C) of 200 Oe at 3 K. Stability assessments through high-temperature magnetometry and temperature-dependent X-ray diffraction reveal a Curie temperature (T_C) of approximately 600 K and a decomposition temperature around 700 K. In contrast, Co₃ZnN undergoes a low-temperature transition near 40 K, accompanied by lower coercivity. Previous computational studies predicted a ferromagnetic ground state for Co₃PdN, and we validate this by showing that the total energy of ferromagnetic Co₃PdN is significantly lower than various antiferromagnetic configurations, by at least +88 meV/atom. Additionally, we present magnetotransport data collected from epitaxial Co₃PdN films grown on SrTiO₃ and MgO substrates. We compare Co₃PdN to Co₃PtN which, despite also being predicted as stable, does not adopt the antiperovskite structure.
This work provides the first experimental confirmation of the Co₃PdN, Co₃ZnN antiperovskite phase, highlighting its potential for further research into its magnetoelectric properties, as well as encouraging exploration of other Co₃AN compounds waiting experimental realization.