title: Room-temperature ferromagnetism in doped face-centered cubic fe nanoparticles.
abstract: The magnetism of Fe and its alloys has been at the center of scientific and technological interest for decades. Along with the ferromagnetic nature of body-centered cubic Fe, the magnetic properties of face-centered cubic (fcc) Fe have attracted much attention. It is well known that fcc Fe is thermodynamically unstable at ambient conditions and not ferromagnetic. Contrary to what is known, we report that elongated nanoparticles of fcc Fe, grown within graphitic nanotubes, remain structurally stable and appear ferromagnetic at room temperature. The magnetic moment (2+/-0.5 microB) in these nanoparticles and the hyperfine fields for two different components of 57Fe (33 and 21 T), measured by Mössbauer spectroscopy, are explained by carbon interstitials in the expanded fcc Fe lattice, that is, FeC(x) where x approximately 0.10, which result in the formation of a dominant Fe4C stoichiometry. First-principles calculations suggest that the ferromagnetism observed in the fcc Fe is related to both lattice expansion and charge transfer between iron and carbon. The understanding of strain- and dopant-induced ferromagnetism in the fcc Fe could lead to the development of new fcc Fe-based alloys for magnetic applications.
authors.affiliation: Department of Electrical and Computer Engineering and Center for Computation and Technology, Louisiana State University, Baton Rouge, LA 70803, USA. weib@ece.lsu.edu
authors.forename: Bingqing
authors.initials: B
authors.lastname: Wei
authors.forename: Mutsuhiro
authors.initials: M
authors.lastname: Shima
authors.forename: Ranjit
authors.initials: R
authors.lastname: Pati
authors.forename: Saroj K
authors.initials: SK
authors.lastname: Nayak
authors.forename: David J
authors.initials: DJ
authors.lastname: Singh
authors.forename: Renzhi
authors.initials: R
authors.lastname: Ma
authors.forename: Yubao
authors.initials: Y
authors.lastname: Li
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Bando
authors.forename: Saburo
authors.initials: S
authors.lastname: Nasu
authors.forename: Pulickel M
authors.initials: PM
authors.lastname: Ajayan
mesh_terms: D003460:Crystallization / Q000379:methods*; D006108:Graphite / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D046911:Macromolecular Substances / Q000737:chemistry; D008280:Magnetics; D008422:Materials Testing; D008968:Molecular Conformation; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D036103:Nanotechnology / Q000379:methods*; D010316:Particle Size; D013499:Surface Properties; D013696:Temperature
chemical_list: D046911:Macromolecular Substances; D006108:Graphite; D007501:Iron