Enhancing Electron Correlation at a 3d Ferromagnetic Surface

Abstract

Spin‐resolved momentum microscopy and theoretical calculations are combined beyond the one‐electron approximation to unveil the spin‐dependent electronic structure of the interface formed between iron (Fe) and an ordered oxygen (O) atomic layer, and an adsorbate‐induced enhancement of electronic correlations is found. It is demonstrated that this enhancement is responsible for a drastic narrowing of the Fe d‐bands close to the Fermi energy (EF) and a reduction of the exchange splitting, which is not accounted for in the Stoner picture of ferromagnetism. In addition, correlation leads to a significant spin‐dependent broadening of the electronic bands at higher binding energies and their merging with satellite features, which are manifestations of a pure many‐electron behavior. Overall, adatom adsorption can be used to vary the material parameters of transition metal surfaces to access different intermediate electronic correlated regimes, which will otherwise not be accessible. The results show that the concepts developed to understand the physics and chemistry of adsorbate–metal interfaces, relevant for a variety of research areas, from spintronics to catalysis, need to be reconsidered with many‐particle effects being of utmost importance. These may affect chemisorption energy, spin transport, magnetic order, and even play a key role in the emergence of ferromagnetism at interfaces between non‐magnetic systems.

Experimental Evidences on Magnetism-Covalent Bonding Interplay in Structural Properties of Solids and during Chemisorption

“…Other authors have reported a strong Dzyaloshinskii-Moriya interaction [3] induced by the chemisorption of oxygen on a FM Ni layer at room temperature via spin-polarized low-energy electron microscopy (SPLEEM) [110]. Others authors have observed a change in the electron correlation on the FM catalyst surface due to the adsorption of O atoms [111]. Another interesting example is the work of M. Kurahashi and Y. Yamauchi on O 2 adsorption over an in-plane magnetized Ni(111) film carried out using spin-and alignment-resolved chemisorption techniques [112,113].…”

“…Another interesting example is the work of M. Kurahashi and Y. Yamauchi on O 2 adsorption over an in-plane magnetized Ni(111) film carried out using spin-and alignment-resolved chemisorption techniques [112,113]. Their results show that the sticking probability of O 2 over magnetized Ni (111) film is different with parallel and antiparallel spin orientations of the paramagnetic molecule, with respect to the majority of the spins' direction on the catalyst surface. The preferred O 2 spin orientation is the one antiparallel to the spin orientation of the FM catalyst.…”

Insights into Heterogeneous Catalysis on Surfaces with 3d Transition Metals: Spin-Dependent Chemisorption Models and Magnetic Field Effects

“…Even for metallic systems, it may be necessary to go beyond the one-electron picture, as suggested by the recent work of Janas et al, 28 in which the authors discuss how the adsorption of oxygen atoms on the surface of ferromagnetic iron leads to a While the above study reports that chemisorption affects band ferromagnetism by collapsing the exchange splitting close to the Fermi level, there are other studies that report the opposite behavior. In certain 3d transition metals, chemisorption may affect the Stoner criterion for the appearance of magnetism, where the interface between metallic thin films and C60 molecular layers modifies the states of metal in such a way that they can overcome the Stoner criterion, resulting in the emergence of ferromagnetic behavior at room temperature in nonferromagnetic materials.…”

“…Even for metallic systems, it may be necessary to go beyond the one-electron picture, as suggested by the recent work of Janas et al., in which the authors discuss how the adsorption of oxygen atoms on the surface of ferromagnetic iron leads to a breakdown of the Stoner-like picture of band ferromagnetism. This is evidenced by the reduction of the exchange splitting, the narrowing and localization of hybrid Fe–O states, and the appearance of spin-polarized adsorbate-FM satellite features.…”