Electronic structure and magnetism of strained bcc phases across the fcc to bcc transition in ultrathin Fe films

Abstract

We investigated the electronic structure of the bcc metastable phases involved in the fcc to bcc transition of Fe. Ultrathin Fe films were grown on a 2-monolayer (ML) Ni/W(110) substrate, where a fcc lattice is stabilized at low Fe coverages and the transition proceeds through the formation of bcc nuclei showing a specific "Kurdjumov-Sachs" orientation with the substrate. A comprehensive description of the electronic structure evolution is achieved by combining spin-resolved UV photoemission spectroscopy and ab initio calculations. According to our results, an exchange-split band structure is observed starting from 2 ML of Fe, concomitant with the formation of ferromagnetic bcc nuclei. Continuous modifications are observed in the spin-resolved photoemission spectra for increasing Fe coverage, especially for what concerns the minority states, possibly indicative of the progressive relaxation of the strained bcc phase starting from the bcc/fcc interface.

Magnetic behavior of metastable Fe films grown on Ir(1 1 1)

“…At 5 ML, Fe starts to show some residual magnetization and it is fully magnetized at remanence above 8 ML. Consistent with our previous results on the growth of Fe on the fcc 2 ML Ni/W(1 1 0) substrate [34], the overall lineshape evolution is indicative of the formation and relaxation of the bcc Fe phase.…”

“…Starting from 5 ML, a small positive (negative) polarization signal is detected around −1.0 (−0.4) eV, then evolving in feature B (B′) in the majority (minority) spin channel. Features B and B′ are clearly resolved at large Fe coverages and are characteristic of photoemission from exchange-split bulk states located along the ΓN direction of the bcc Fe Brillouin zone (BZ), close to the Γ point [11,34]. Consistent with the non-ferromagnetic character of the Ir substrate, peak A is visible in both spin channels.…”

“…We therefore assign the overlayer features observed in figures 3 and 4(a) to photoemission from a strained bcc Fe phase. In analogy with [34], we interpret the BE evolution of feature B′ towards E F as a consequence of the relaxation of the bcc phase with increasing Fe coverage. Inverse photoemission from the Ir(1 1 1) substrate (figure 4(b)) is characterized by a single feature (labeled C) located at an energy of about 0.75 eV.…”

Oxygen contribution to the magnetic response of ultrathin Fe/Ni multilayers grown on Fe-p(1 × 1)O

“…An accurate comparison between our experimental results and the layer wise simulation of Fe and Ni electronic structure is not straightforward for those states characterized by a strong dispersion in the direction perpendicular to the surface, such as the empty majority feature C, that we assigned to photoemission from a bulk state. Nevertheless, it appears likely to us that the observed modifications in the Fe overlayer electronic structure have to be ascribed to a crystalline quality worsening or a structural relaxation of the overlayer, as already observed in homo-and hetero-epitaxial systems, respectively [34,35], not captured by the simulations, rather than the effect of hybridization with the Ni buffer layer.…”

Intercalation from the Depths: Growth of a Metastable Chromium Carbide between Epitaxial Graphene and Ni(111) by Carbon Segregation from the Bulk

“…The C rich chemical composition of the film does not resemble any reported stoichiometry of stable Cr carbides in the bulk form. However, it is well-known that, due to the epitaxial constraints imposed by the substrate, nanometer thick films can crystallize also as phases, which are different from their parent bulk materials. − …”