The effects of Cobalt doping on the structural, electronic, magnetic, and thermodynamic characteristics of the L10-FeNi alloy: First-principle calculations

This study conducts a computational analysis employing density functional theory (DFT) to investigate the effects of Cobalt doping as substitutional defects on the structural, electronic, magnetic, and thermodynamic characteristics of the L $1_0-$ FeNi alloy. The aim of this study was to explore their potential applications as alternatives to rare-earth permanent magnets. Two types of substitutional Co-doping (O_Ni/O_Fe) in the Ni/Fe-site of the parent alloy have been investigated. The computed formation energy indicates that the incorporation of cobalt defects increases the structural stability of tetragonally distorted L₁₀FeNi via Co-doping. The results we obtained demonstrate that the FeNi:Co (O_Ni) in the L₁₀-structure has a large enhancement in magnetic moments and saturation magnetization (M_s), whereas for the FeNi:Co (O_Fe), has a small reduction in M_s. Furthermore, reducing the concentration of cobalt in L₁₀ FeNi:Co alloys is advantageous in diminishing the volumetric thermal expansion coefficient, consequently lowering the Debye temperature and weakening atom interactions. Therefore, Co-substituted FeNi alloys hold promise as potential candidates for rare-earth-free permanent magnets.