Both collinear and noncollinear magnetic structures of FeMn with L1 0 atomic ordering were determined from total-energy full-potential linearized augmented plane-wave calculations incorporating noncollinear magnetism with no shape approximation for the magnetization density. Different spin-density orientations for the different band states are observed on a smaller length scale inside an atom. The presence of the intra-atomic noncollinear magnetism enhances the stability of the 3Q noncollinear magnetic structure, in which the magnetic moments align toward the center of the cell of four atoms, thus becoming the lowest-energy state of the structures considered.Antiferromagnetic ͑AFM͒ materials have attracted great attention in technological applications since the discovery of the exchange bias 1 associated with the interface between ferromagnetic ͑FM͒ and AFM materials. Among these, fcc FeMn is one of the useful candidates as an exchange bias AFM material. 2,3 Despite its importance, its magnetism is not well understood quantitatively since the experimental determinations of the magnetic properties are difficult due to the absence of a net magnetization in an AFM material.So far three models of magnetic structures in disordered FeMn have been proposed from experiments: 4 -7 a collinear AFM (1Q) structure and two noncollinear magnetic (2Q and 3Q) structures, as shown in Fig. 1. The magnetic Mn and Fe moments in the 1Q structure are in a collinear state while those in the 2Q structure align perpendicular to each other. For the 3Q structure, the magnetic moments align toward the center of the cell of four atoms, i.e., along different ͗111͘ directions. Originally, Kouvel and Kasper 4 first detected long-range AFM ordering by neutron-diffraction measurements, and found that either the 1Q or the 3Q structure could explain the data. Later, by means of Mössbauer and neutron diffraction, Endoh and Ishikawa 5 determined a magnetic phase diagram in a whole composition range of Fe x Mn 1Ϫx and expected the 3Q structure at the equiatomic composition. More recently, however, Kennedy and Hick 6 suggested the 2Q structure from Mössbauer transmission spectra and Bianti et al. 7 proposed the 1Q structure based on inelastic neutron experiments. Thus, the experiments still have an ambiguity in the determination of the magnetic ground state.From the theoretical point of view, using first-principles total-energy calculations Kübler et al. 8 and several other researchers 9,10 reported that the 2Q structure is energetically more stable than the other two structures when restricted to an L1 0 ordered state. Furthermore, their calculations were based on the atomic sphere approximation for the magnetization density, i.e., they assumed only one local spinquantization axis in each atomic sphere and the corresponding magnetization density was spherically averaged. Although these calculations have revealed the physical nature of the magnetism of FeMn, their energy differences are quite small and so quantitative highly precise predictions are nec...

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We investigate the domain walls in ferromagnetic Fe and antiferromagnetic NiMn with the first principles full-potential linearized augmented plane-wave method including intra-atomic noncollinear magnetism. In both cases, the self-consistent results demonstrate that the magnetization changes continuously from one orientation to another as seen in a Bloch wall. The formation energy of the domain wall (⌬E DW ) significantly decreases when the wall thickness increases, which leads to an exchange stiffness of 1.13ϫ10 Ϫ11 J/m for Fe and 1.43ϫ10 Ϫ11 J/m for NiMn. The predictions agree with those determined separately for Fe from a phenomenological calculation.