Crystal orientation, surface termination and film thickness effects on the perpendicular magnetic anisotropy of Mn 4 N films: a first-principles study

Anti-perovskite Mn4N is a promising ferrimagnet with perpendicular magnetic anisotropy (PMA), making it attractive for high-performance and thermally stable nonvolatile memory devices. Using first-principles calculations, we systematically investigate the effects of crystal orientation, surface termination, and film thickness on the PMA of Mn4N slabs cleaved along the [001] and [010] crystallographic directions of bulk Mn4N. The results indicate that the MnN-terminated slabs are energetically the most stable for both orientations, named as MnN-001 and MnN-010 slab models, respectively. The MnN-001 slab retains a strong PMA (4.42 mJ/m2 for 5-monolayer model), attributable to its preserved tetragonal symmetry and the cumulative, uniformly positive contributions from each atomic layer. In contrast, the MnN-010 slab undergoes an orthorhombic distortion, leading to a significantly reduced PMA (0.44 mJ/m2 for 5-monolayer model), as a result of the cancellation between positive and negative PMA contributions from odd and even layers, respectively. Furthermore, as Mn4N slab thickness increases from 3 to 9 monolayers, the areal PMA of the MnN‑001 model increases progressively, while its volumetric counterpart gradually decreases and converges towards the bulk magnetocrystalline anisotropy limit; the MnN‑010 model exhibits a weak PMA that increases slightly from 3 to 5 monolayers and then saturates. This work clarifies how surface orientation, termination, and thickness affect the PMA of Mn4N, providing a foundation for its application in perpendicular magnetic storage.