Structure and magnetism of the(2×2)-FeO(111) surface

Abstract

Based on ab initio calculations we determine the features and relative stability of different models proposed to describe the (2 × 2)-FeO(111) reconstruction. Our results suggest that both wurtzite and spinel-like environments are possible, and their coexistence explains phenomena of biphase ordering. The surface phase diagram reflects a competition of charge and magnetic compensation effects, and reveals the important influence of the substrate on the final surface structure. Though antiferromagnetic couplings are dominant, frustration and the delicate balance of surface and bulk exchange interactions lead to a net surface magnetization that accounts for the large measured values.

Stability, magnetic order, and electronic properties of ultrathin Fe3O4 nanosheets

“…Moreover, the new structure shows mixed coordination: it comprises one close-packed Fe layer with octahedral coordination at the center of the film and two close-packed Fe layers with Fe tetrahedrally coordinated next at the film/substrate and film/gas-phase interfaces. Such surface layer arrangements are of the same tetrahedral/wurtzite type as previously reported for rocksalt FeO on Ru(0001) [18,19] and CoO on Ir(100) [20][21][22]. However, the layer stacking sequence is different from that in previous reports [18][19][20][21][22], as the stacking faults effectively cancel when the structure is only three layers thick.…”

“…Such surface layer arrangements are of the same tetrahedral/wurtzite type as previously reported for rocksalt FeO on Ru(0001) [18,19] and CoO on Ir(100) [20][21][22]. However, the layer stacking sequence is different from that in previous reports [18][19][20][21][22], as the stacking faults effectively cancel when the structure is only three layers thick. Thus, the new phase has a tetrahedral-octahedral-tetrahedral (TOT) layer combination with the close-packed Fe layers ordered in an ABC stacking sequence.…”

“…The exchangecorrelation functional is described by the generalized gradient approximation using the Perdew, Burke, and Ernzerhof (PBE) formula [30,31]. Because noncollinear components have been found to be small for FeO [19], we model the spins collinearly. The electronic wave functions are expanded in plane waves and the reciprocal space is discretized by means of acentered k-point grid generated using the Monkhorst-Pack scheme [32].…”

“…However, as discussed in Refs. [18,19], the local spin structure may differ in the proximity of surfaces with Fe ions in tetrahedral positions. Thus, to identify the lowest-energy configuration, we investigate different spin orderings.…”

Study of the critical behavior of antiferromagnetic thin films by computer modeling

“…The difference in the values of the surface and bulk exchange integrals was calculated from the first principles in the papers [9,10], and experimentally verified in [11,12]. In the paper [13], on the basis of the first-principles calculations it was shown that for FeO the surface energy depends linearly on the chemical potential. In the paper [9], the first-principles calculations for Gd revealed that the distance between atoms in the bulk of a crystal equals 3.52 A, whereas on the surface it equals 3.64 A, which leads to a difference in the values of exchange integrals, being J S = 1.25 and J B = 1.51, respectively, and consequently, their ratio is R = J S / J B = 0.83.…”