Institute of Solid State Chemistry, Yekaterinburg 620990, Russia.
J Phys Condens Matter. 2010 Aug 11;22(31):316002. doi: 10.1088/0953-8984/22/31/316002. Epub 2010 Jul 8.
Density functional theory calculations were performed to study the structure and magnetic properties of bcc (α) and fcc (γ) Fe with 3 at.% carbon and manganese impurities. We find that all bcc-based Fe, Fe-C and Fe-Mn-C phases exhibit a ferromagnetic (FM) ground state, while the antiferromagnetic double-layer (AFMD) state is lowest in energy within the collinear spin approach in fcc Fe, Fe-C and Fe-Mn-C phases. However, the carbon and manganese impurities affect the local magnetic interactions significantly. The states with opposite manganese magnetic moments are quasi-degenerate in bcc Fe-Mn alloy, whereas octa-site carbon stabilizes ferromagnetic coupling of the nearest manganese atom with the Fe host. We demonstrate that the antiferromagnetic (AFM) fcc Fe-C and Fe-Mn-C alloys are intrinsically inhomogeneous magnetic systems. Carbon frustrates the local magnetic order by reorientation of magnetic moments of the nearest Mn and Fe atoms, and favors their ferromagnetic coupling. The competition between ferromagnetic and antiferromagnetic Fe-Fe and Fe-Mn interactions and the local magnetovolume instability near carbon may give rise to the spin-glass-like regions observed in austenitic Fe-Mn-C alloys.
采用密度泛函理论计算研究了 bcc(α)和 fcc(γ)Fe 中 3at.%碳和锰杂质的结构和磁性。我们发现，所有基于 bcc 的 Fe、Fe-C 和 Fe-Mn-C 相都表现出铁磁（FM）基态，而在 fccFe、Fe-C 和 Fe-Mn-C 相中，共线自旋方法中反铁磁双层（AFMD）态的能量最低。然而，碳和锰杂质对局部磁相互作用有显著影响。在 bccFe-Mn 合金中，具有相反锰磁矩的态是准简并的，而八面体碳稳定了最近的锰原子与 Fe 主体之间铁磁耦合。我们证明了反铁磁（AFM）fccFe-C 和 Fe-Mn-C 合金本质上是不均匀的磁性系统。碳通过重新取向最近的 Mn 和 Fe 原子的磁矩来破坏局部磁有序，并有利于它们的铁磁耦合。在碳附近，铁磁 Fe-Fe 和 Fe-Mn 相互作用与局部磁-体积不稳定性之间的竞争可能导致在奥氏体 Fe-Mn-C 合金中观察到的类自旋玻璃区域。
