Structural Properties of Iron Nitride on Cu(100): an Ab-initio Molecular Dynamics study
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Structural Properties of Iron Nitride on Cu(100): an Ab-initio Molecular Dynamics study Dodi Heryadi1 and Udo Schwingenschlögl2 1 Supercomputing Laboratory, King Abdullah University of Science and Technology (KAUST), Kingdom of Saudi Arabia 2 Physical Science & Engineering, King Abdullah University of Science and Technology (KAUST), Kingdom of Saudi Arabia ABSTRACT Due to their potential applications in magnetic storage devices, iron nitrides have been a subject of numerous experimental and theoretical investigations. Thin films of iron nitride have been successfully grown on different substrates. To study the structural properties of a single monolayer film of FeN we have performed an ab-initio molecular dynamics simulation of its formation on a Cu(100) substrate. The iron nitride layer formed in our simulation shows a p4gm(2x2) reconstructed surface, in agreement with experimental results. In addition to its structural properties, we are also able to determine the magnetization of this thin film. Our results show that one monolayer of iron nitride on Cu(100) is ferromagnetic with a magnetic moment of 1.67 μB. INTRODUCTION Epitaxial layers of iron nitrides have received a growing interest due to their unique physical properties as well as their potential applications in industry. Fe4N, in particular, has been noted as being suitable for high-density magnetic storage devices. Successful attempts in growing thin layers of iron nitride have been reported in the literature. Boorsa et al., for example, were able to grow pure γ ′ -Fe4N films on (001) MgO substrates using molecular beam epitaxy of iron in the presence of atomic nitrogen from a radio frequency atomic source [1,2]. Nanostructured layers of γ ´-Fe4N were also successfully grown on the Cu(100) surface by evaporating Fe in a flux of atomic nitrogen produced from a plasma source [3-5]. Another method to grow thin layers of γ ′ -Fe4N on Cu(100) surfaces is to deposit iron atoms on a N-adsorbed Cu(100) substrate [6]. Magnetic and structural properties of iron nitrides have been studied extensively. It has been shown that the magnetic moments of the FeN system depend on its phase [7,8]. For the cubic phases, the γ ´´-ZnS-type nitride is nonmagnetic, whereas the γ ´´-NaCl-type nitride is anti-ferromagnetic. Iron nitrides on the iron-rich side of the phase diagram are mostly ferromagnetic. For structural properties, Takagi et al. have recently reported that iron nitride thin films on Cu(100) exhibit a p4gm(2x2) structure with a Fe/N composition ration of 2:1 for 1 monolayer (ML) and 4:1 for 2 ML [6]. They found a strong relationship between the magnetic properties of the films and their morphologies, where the magnetic moment increases as the number of layers increases. In an earlier study, Galego et al. also have reported the formation of iron nitride layers on a Cu(100) substrate with p4gm(2x2) structure [3-5].
In the present work we have performed an ab-initio molecular dynamics simulation to describe the formation of a ML of iron nitride on a Cu(100) substrate
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