Tuning the magnetic properties of Mn₂AC (A = Al, Ga, Ge) MAX-phase thin films via dimensionality, strain, and surface termination: DFT study

Abstract

Using density functional theory (DFT-GGA), we study the magnetic and electronic properties of Mn 2 AC (A = Al, Ga, Ge) MAX-phase thin films, focusing on the effects of surface termination and in-plane strain. The magnetic ground state strongly depends on surface type: Mn C terminated films retain the bulk magnetic orders (FM for Mn 2 AlC, AFM3 for Mn 2 GaC, AFM2 for Mn 2 GeC); A–Mn termination switches Mn 2 GaC to FM and Mn 2 GeC to AFM1, while Mn Mn termination stabilizes AFM3 for all compounds, and A–A termination yields FM for all. In-plane strain triggers sharp transitions at low critical strains (±2%) for Mn C terminated Mn 2 AlC and Mn 2 GaC, whereas Mn 2 GeC is more robust. All thin films are metallic, with the bulk Mn 2 GeC pseudogap disappearing in films. Surface Mn atoms exhibit enhanced magnetic moments (up to 3.7 μ B ) compared to inner layers (1.8–2.3 μ B ). These results demonstrate that thickness, strain, and surface chemistry act as independent control parameters for magnetism in Mn 2 AC films, offering pathways for mechanically and chemically switchable spintronic devices.