Magnetocrystalline effects on the subsurface hydrogen diffusion in γ-Fe(0 0 1)

Abstract

The effect of magnetism on hydrogen adsorption and subsurface diffusion through facecentred cubic (fcc) γ-Fe(001) was investigated using spin-polarised density functional theory (s-DFT). The non-magnetic (NM), ferromagnetic (FM), and antiferromagnetic single (AFM1) and double layer (AFMD) structures were considered. For each magnetic state, the hydrogen preferentially adsorbs at the fourfold site, with adsorption energies of 4.07, 4.12, 4.03 and 4.05 eV/H atom for the NM, FM, AFM1 and AFMD structures. A total barrier of 1.34, 0.90, 1.32 and 1.25 eV and a bulk-like diffusion barrier of 0.6, 0.2, 0.4 and 0.3 eV were calculated for the NM, FM, AFM1 and AFMD magnetic states. The Fe atoms nearest to the H atom exhibited a reduced magnetic moment, whereas the nextnearest neighbour Fe atoms exhibited a non-negligible local perturbation in the magnetic moment. The presence of magnetically ordered structures has a minimal influence on the minimum energy path for H diffusion through the lattice and on the adsorption of H atoms on the Fe(001) surface, but we computed a significant reduction of the bulk-like diffusion barriers with respect to the non-magnetic state of fcc γ-Fe.

Insight into structural stability and helium diffusion behavior of Fe–Cr alloys from first-principles

“…Looking at Table 2 , we note that the optimized lattice constants ( a = 3.420, c = 3.685 Å) in the AFM state are slightly different from experimental values ( a = 3.56 Å) obtained by Acet et al 40 However, the relaxed lattice constants ( a = c = 3.446 Å) in the NM state are obviously distorted compared with the experimental results ( a = 3.645 Å) of Acet et al 40 Similar situations have been encountered in other theoretical studies. Compared with other theoretical results, our lattice constants in the AFM state are similar to the values a = 3.48 and a = 3.50 Å calculated by Jiang et al 35 using PAW and FLAPW methods respectively, which are close to a = 3.47 and c = 3.75 Å of Marcus et al , 41 and consistent with a = 3.420 Å of Medvedeva et al 42 Similarly, the lattice constants a = 3.446 Å in the NM state are close to a = 3.45 and a = 3.46 Å of Jiang et al , 35 and are in good agreement with a = 3.443 Å (average value of LDA and GGA) from Yu et al , 5 similar to a = 3.44 Å in Marcus et al , 41 and matched with a = 3.45 Å of Medvedeva et al 42 The computed axes ratios in the AFM and NM states are 1.077 and 1.000, respectively, which are in good agreement with 1.09 (1.07) and 1.00 obtained by Chohan et al 12 and Medvedeva et al 42 The total spin orbital magnetic moment calculated by ours is 0.000 μ B , which is different from the experimental value 0.70 μ B of Abrahams et al , 43 and is more different from the theoretical value of others. 13,15,35,40,42,44,45 As we all know, the characteristic of the AFM state is that the net magnetic moment per unit volume is zero without external magnetic field, and it does not show magnetism in macroscopical.…”

“…For Fe-Cr alloys austenite, the single-layer antiferromagnetism (AFM), double-layer anti-ferromagnetism (AFMD), ferromagnetic (FM) and non-magnetic (NM) magnetic states were considered. [12][13][14][15]…”

Energetics of hydrogen adsorption and diffusion for the main surface planes and all magnetic structures of γ-iron using density functional theory

“…Since the effects of hydrogen diffusion on the exact geometry of the unit cells and the magnetic properties were already discussed in previous publications, 3,4 we focus here mainly on the energetics of the hydrogen adsorption and diffusion process for the twelve cases which are a combination of three different surface planes, namely (100), (110), and (111), and four different magnetic structures, namely NM, FM, AFM1, and AFMD, for g-Fe. The numerical results are summarised in Table 1 and the respective potential energy surfaces depicted in Fig.…”

“…This publication concludes a series of papers in which we modelled the adsorption of oxygen and hydrogen on bcc iron, 1,2 and, more relevant to the current paper, the hydrogen adsorption on and sub-surface diffusion through g-Fe. 3,4 The last two publications focussed on austenitic (stainless) steel as opposed to ferritic or ferritic-martensitic steels, in particular the facecentred cubic (fcc) austenitic steel phase, termed austenite or g-Fe. In ref.…”

Exchange-bias dependent diffusion rate of hydrogen discovered from evolution of hydrogen-induced noncollinear magnetic anisotropy in FePd thin films

“…2(d) and 2(e). As hydrogen atoms would most probably advance on minimum-energy paths for diffusion [64], the dependence of the diffusion rate on the initial EB may indicate changes of minimum-energy paths due to variations of magnetic ordering. Then, at n = 7 in Fig.…”