Enhancement of the spin polarization of an Fe₃O₄(100) surface by nitric oxide adsorption

Abstract

The geometric, electronic and magnetic properties of a nitric oxide (NO) adsorbed Fe3O4(100) surface have been investigated using density functional theory (DFT) calculations. NO molecules preferentially bond with surface Fe(B) atoms via their N atoms. The generalized gradient approximation (GGA) is not recommended to be used in such a strongly correlated system since it provides not only an overestimation of the adsorption energy and an underestimation of the Fe(B)-N bond length, but also magnetic quenching of the adsorbate and the bonded Fe(B) atoms. In contrast, a tilted geometry and magnetization of the adsorbate and the bonded Fe(B) atom are obtained after including the strong on-site Coulomb interactions through a Hubbard term (GGA+U). The spin-down 2π* states of the NO molecule are filled and broadened due to the adsorbate-substrate interaction and the molecule-molecule interaction. The surface spin polarization close to the Fermi level is expected to be greatly enhanced by the NO adsorption which has significance for interface design in spintronic devices.

Surface Study of Fe3O4 Nanoparticles Functionalized With Biocompatible Adsorbed Molecules

“…However, diamagnetic coating of nanoparticles causes decrease of M s due to introducing surface spin disorder. Previously reported results provided evidences on modification of magnetic properties of Fe 3 O 4 due to adsorption (Li et al, 2018), grain size (Liu et al, 2016), and functionalization (Soares et al, 2015). The oxidation of the surface interface of Fe 3 O 4 MNPs I–V is reflected in increasing Fe 2p 3/2 BE values and separation between Fe 2p 3/2 octahedral 2+ component and plasmon loss of Fe 2p 3/2 octahedral 2+ component (ΔFe Oh 2+ ) (Figure 6B), justifying modification of magnetic properties resulting from slight modification of Fe 3 O 4 stoichiometry and spin flipping at the interface of MNPs and functionalizing adsorbed molecules.…”

“…The ideal Fe 3 O 4 atomic ratio of Fe 2+ :Fe 3+ is 1:2, and precisely the ratio of Fe Oh 2+ :Fe Oh 3+ :Fe Th 3+ is 1:1:1. The fitting of Fe 2p spectra accounted for Fe 2+ and Fe 3+ octahedral and Fe 3+ tetrahedral spectra component parameters like Fe 2p 3/2 BE and FWHM values reported in the literature (Yamashita and Hayes, 2008; Poulin et al, 2010; Eltouny and Ariya, 2014; Herng et al, 2015; Liu et al, 2016; Li et al, 2018; Petran et al, 2018). Exemplary Fe 2p spectra fitting results are shown in Figure 4, whereas all the fitted spectra are shown in Supplementary Figure S4.…”

Spin Polarization Enhancement of an Fe3O4(100) Surface by Coadsorption of Atomic Hydrogen and Molecular Nitric Oxide

“…6 In contrast, a NO molecule prefers the Fe(B) site via its N-terminal with an adsorption energy of −0.823 eV. 10 The bonding of NO molecules with metallic atoms has also been observed for CuFe 2 O 4 (100), ZnGaAlO 4 (100), and NiO(100) substrates. 24−26 The geometric structure of (H, NO) coadsorption can be obtained through the adsorption of either a NO molecule on the H-adsorbed (Supporting Information).…”

“…Atomic H is known to prefer the O1 site with a large adsorption energy (−3.154 eV as calculated using GGA + U ) . In contrast, a NO molecule prefers the Fe­(B) site via its N-terminal with an adsorption energy of −0.823 eV . The bonding of NO molecules with metallic atoms has also been observed for CuFe 2 O 4 (100), ZnGaAlO 4 (100), and NiO(100) substrates. − The geometric structure of (H, NO) coadsorption can be obtained through the adsorption of either a NO molecule on the H-adsorbed Fe 3 O 4 (100) surface or a H atom on the NO-adsorbed Fe 3 O 4 (100) surface.…”

“…7,8 We also showed recently that molecular adsorption of NO also leads to a −100% spin polarization at the Fermi level with NO molecules found to bond to surface Fe(B) atoms. 10 However, the half-metallic band width of NO-adsorbed Fe 3 O 4 (001) is much narrower than that of the H-adsorbed system because of the unsaturated surface dangling bonds. Again though, positive spin polarization exists at surface oxygen atoms, which slightly negates the benefits of the NO-adsorbed system.…”