Atomic scale spin‐dependent STM on magnetite using antiferromagnetic STM tips

Abstract

STM tips made from antiferromagnetic MnNi have been used to investigate the atomic structure of the (001) and (111) surfaces of Fe 3 O 4 . The clean (001) surface displays a (√2 × √2)R45° superlattice, which is attributed to charge-ordering on the surface, where Fe 2+ -Fe 2+ and Fe 3+ -Fe 3+ dimers can be discriminated. The oxygenterminated (111) surface is characterized by an hexagonal superlattice with a periodicity of 42 Å. Oxygen vacancies are observed in atomically resolved images of this superlattice. In the presence of an external magnetic field of 60 mT, a significant change in the atomic corrugation in the topmost oxygen layer around each of these defects is observed. The results on both (001) and (111) surfaces are discussed in terms of possible spin polarized effects.

Impact of interface orientation on magnetic coupling in highly ordered systems: A case study of the low-indexedFe3O4/NiOinterfaces

“…This finding is consistent with the octahedral termination reported in Ref. 37, since x-ray absorption by total yield detection has a low probing depth of only Ϸ10 Å at the Fe L edges 38 and consequently is sensitive to the topmost atomic layers of the material.…”

“…This yielded sufficiently good surface stoichiometry Fe 3 37. This termination was reported to occur at a lower annealing temperature of only 850 K. We annealed the ͑001͒-oriented sample at a slightly higher temperature of around 870 K and found a stoichiometry with ␦ = −0.07 based on the analysis of the Fe XMCD signal, i.e., a stronger occupancy of the octahedral sites.…”

Spin mapping at the nanoscale and atomic scale

“…51͑b͒. Similar results were obtained for ͑001͒ surfaces of synthetic Fe 3 O 4 single crystals using ferromagnetic Fe as well as antiferromagnetic MnNi tips ͑Koltun et al, 2001;Shvets et al, 2004͒. The formation of Fe 2+ and Fe 3+ pairs along the ͓110͔-oriented rows of Fe B sites, related to a charge-and spin-ordered state at the ͑001͒ surface of magnetite at room temperature, has been explained by an increase in the metal-insulator ͑Verwey͒ transition temperature at the surface of magnetite, resulting from the reduced coordination and the correspondingly reduced electronic bandwidth at the surface compared to the bulk ͑Coey et al., 1993;Wiesendanger et al, 1994;Shvets et al, 2004͒. Another atomic-resolution SP-STM study concentrated on oxygen vacancies on the ͑111͒ surface of synthetic Fe 3 O 4 crystals ͑Berdunov, Berdunov, Murphy, Mariotto, Shvets, and Mykovskiy, 2004;Murphy et al, 2005͒. In this case a magnetic-field dependent contrast of electronic states around individual oxygen vacancy sites was revealed by SP-STM using antiferromagnetic MnNi tips.…”

One-dimensional structural and electronic properties of magnetite Fe3O4(110)

“…The (0 0 1) [4][5][6][7][8] and (1 1 1) [9][10][11][12][13] surfaces of magnetite have been extensively studied by STM both in single-crystal and thin-film forms and several surface terminations have been proposed. It has been shown for these orientations that the preparation conditions are crucial for the type of termination.…”