Room-temperature ferromagnetism in graphite driven by two-dimensional networks of point defects

• Published in: Nature physics Vol. 5; no. 11; pp. 840 - 844
• Main Authors: Flipse, C. F. J, ervenka, J, Katsnelson, M. I
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01-11-2009; Nature Publishing Group
• Subjects: Anisotropy; Atomic; Boundaries; Carbon; Classical and Continuum Physics; Complex Systems; Condensed Matter Physics; Ferroelectrics; Graphite; Magnetism; Mathematical and Computational Physics; Molecular; Optical and Plasma Physics; Physics; Physics and Astronomy; Theoretical
• ISSN: 1745-2473; 1745-2481
• DOI: 10.1038/nphys1399

Understanding the mechanism of ferromagnetism in carbon-based materials, which contain only
s
and
p
electrons in contrast to traditional ferromagnets based on 3
d
or 4
f
electrons, is challenging. Here, we demonstrate direct evidence for ferromagnetic order locally at defect structures in highly oriented pyrolytic graphite (HOPG) with magnetic force microscopy and in bulk magnetization measurements at room temperature. Magnetic impurities have been excluded as the origin of the magnetic signal. The observed ferromagnetism has been attributed to originate from localized electron states at grain boundaries of HOPG, forming two-dimensional arrays of point defects. The theoretical value of the magnetic ordering temperature based on weak interlayer coupling and/or magnetic anisotropy is comparable to the experimental value. The unusual chemical environment of defects bonded in graphitic networks can reveal the role of the
s
and
p
electrons, creating new routes for spin transport in carbon-based materials.
Ferromagnetism usually only occurs in materials containing elements that form covalent 3
d
and 4
f
bonds. Its occurrence in pure carbon is therefore surprising, even controversial. A systematic magnetic force microscope study indicates that ferromagnetism in graphite is the result of localized spins that arise at grain boundaries.