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Ferromagnetic nanoparticles DOI: 10.1002/smll.200500436

Summary: Ferromagnetic nanoparticles
DOI: 10.1002/smll.200500436
Room-Temperature Ferromagnetism in Doped Face-
Centered Cubic Fe Nanoparticles
Bingqing Wei,* Mutsuhiro Shima,* Ranjit Pati, Saroj K. Nayak,* David J. Singh,
Renzhi Ma, Yubao Li, Yoshio Bando, Saburo Nasu, and Pulickel M. Ajayan*
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 nano-
particles of fcc Fe, grown within graphitic nanotubes, remain structurally
stable and appear ferromagnetic at room temperature. The magnetic
moment (2∆0.5 mB) in these nanoparticles and the hyperfine fields for
two different components of 57
Fe (33 and 21 T), measured by MÁssbauer
spectroscopy, are explained by carbon interstitials in the expanded fcc Fe
lattice, that is, FeCx where x%0.10, which result in the formation of a
dominant Fe4C stoichiometry. First-principles calculations suggest that the


Source: Ajayan, Pulickel M. - Department of Mechanical Engineering and Materials Science, Rice University


Collections: Materials Science