Theoretical Study on the Half‐Metallicity and Magnetic Characteristics in Bulk and Orientation‐Dependent Thin Films of Co ₂ MnSb and CoFeMnSb Heusler Alloys

Based on first‐principles calculations, this study systematically investigates the electronic structures and magnetic properties of the ternary Co 2 MnSb and the quaternary CoFeMnSb Heusler alloys in bulk form as well as thin films with (001), (110), and (111)‐orientations. The results demonstrate that both bulk Co 2 MnSb and CoFeMnSb exhibit typical half‐metallicity, characterized by well‐defined minority‐spin band gaps at the Fermi level. For thin films, the half‐metallicity of Co 2 MnSb is highly sensitive to crystallographic orientation and surface termination. Specifically, Mn‐terminated surfaces in the (001) and (111) orientations preserve nearly 100% spin polarization. In contrast, the CoFeMnSb thin film can maintain stable high spin polarization under both Mn‐terminated and Sb‐terminated surfaces, with certain surface termination configurations reaching 100%. Further magnetic investigation indicates that the introduction of Fe induces significant redistribution of d ‐electron magnetic moments among Co, Fe, and Mn, in which the Co magnetic moment is suppressed, while the contributions from Fe and Mn magnetic moments are enhanced. The above results confirm that the maintenance of high spin polarization is closely related to orbital‐resolved magnetic regulation and surface state suppression.