THE SEARCH FOR STABLE ROOM-TEMPERATURE BULK FERROMAGNETIC GRAPHITE#
Dr. Fernando M. Araújo-Moreira*
Grupo de Materiais e Dispositivos (GMD); Centro Multidisciplinar de Desenvolvimento de Materiais Cerâmicos
(CMDMC); Departamento de Física e Engenharia Física/UFSCar,
CP 676, São Carlos, SP, Brazil, CEP 13565-905
The search for macroscopic magnetic ordering phenomena in pure carbon is a very
important field in the frontiers of physics, chemistry and materials science. The production of
macroscopic bulk carbon magnetic material would have immediate impact through novel
applications of this material in engineering, as well as in medicine and biology as a unique
biocompatible magnetic material[1]. We have recently reported a novel and inexpensive chemical
route leading to obtain macroscopic quantities of room temperature magnetic carbon obtained
from synthetic pristine graphite[2,3]. We have extended the process to obtain ferromagnetic graphite
to natural pristine graphite, which opens new perspectives to possible application of this material.
We report on the structural and magnetic properties of pure bulk ferromagnetic graphite,
obtained by a chemical route previously described[2,3]. This magnetic graphite has been obtained by
a vapor reaction consisting of a controlled etching on the graphite structure[2,3]. By magnetic force
microscopy we have verified that its magnetic properties are related to the topographic defects
introduced in the pristine material. Also, the magnetic properties have been verified through
magnetization measurements as a function of temperature and applied magnetic field. At low
temperatures (2 K) the saturation magnetization reaches a value of 0.58 emu/g, leading to a defect
concentration of 1250 ppm. The system is highly irreversible due to the inhomogeneity of the
distribution of defects in the material. Two transition temperatures are detected, Tc1=115(5) K and
Tc2 =315(5) K. These transitions could be associated to the weak coupling between ferromagnetic
regions related to defects and to the ferromagnetism inside the those regions.
We have also performed ab initio calculations for single-atom vacancies in graphene[4]. The
vacancies induced in graphene induce a re-hybridization of the 2s and 2px,y orbitals of C which
partially account for the magnetic moments. Upon H, N, or O adsorption on the magnetic center, this
rehybridization is suppressed, and different mechanisms play a role in the formation of magnetic
moments in the system. We investigate and discuss the rich variety of mechanisms found.
Finally, in this talk we show our more recent results obtained from graphite, such as the
defect-mediated half-metal behavior in zigzag graphene nanoribbons[5], the temperature
oscillations of magnetization observed in nanofluid ferromagnetic graphite[6], the synthesis,
characterization and magnetic properties of room-temperature nanofluid ferromagnetic graphite[7],
the manifestation of quantum effects in nanogranular magnetic graphite[8], and the manifestation of
finite temperature size effects in nanogranular magnetic graphite[9].
[1] T. L. Makarova; Magnetic properties of carbon structures; Semiconductors 38; 615–38 (2004).
[2] A. W. Mombrú, H. Pardo, R. Faccio, O. F. de Lima, A. J. C. Lanfredi, C. A. Cardoso, E. R. Leite, G. Zanelatto and F. M. AraújoMoreira; Phys. Rev. B 71, 10, 404-407 (2005).
[3] H. Pardo, R. Faccio, A. W. Mombrú, O. F. de Lima and F. M. Araújo-Moreira; Carbon 44, 565-569 (2006).
[4] R. Faccio, H. Pardo, P. A. Denis, R. Yoshikawa Oeiras, F. M. Araújo-Moreira, M. Veríssimo-Alves, and A. W. Mombrú; Phys.
Rev. B 77, 035416 (2008).
[5] R. Y. Oeiras, F. M. Araújo-Moreira, and E. Z. da Silva; Phys. Rev. B 80, 073405 (2009).
[6] S Sergeenkov, N.S. Souza, C. Speglich, V. A. G. Rivera, C.A. Cardoso, H. Pardo, A.W. Mombru, and F.M. Araujo-Moreira; J.
Phys.: Condens. Matter 21, 495303 (2009).
[7] N. S. Souza, S. Sergeenkov, C. Speglich, V. A. G. Rivera, C. A. Cardoso, H. Pardo, A. W. Mombrú, A. G. Rodrigues, O. F. de Lima
and F. M. Araújo-Moreira; Applied Physics Letters (2009).
[8] S. Sergeenkov, N.S. Souza, C. Speglich, V.A.G. Rivera, Cardoso, H. Pardo, A.W. Mombru, F.M. Araujo-Moreira; JETP Letters
(2009).
[9] S. Sergeenkov, N.S. Souza, C. Speglich, V.A.G. Rivera, C.A. Cardoso, H. Pardo, A.W. Mombru and F.M. Araujo-Moreira;
Journal of Applied Physics (2009).
_________________________________________________________________________________
(#) To be presented as an Invited Talk at the International Conference on Science and Technology of Synthetic Metals 2010
(ICSM 2010), which will be held at Kyoto International Conference Center (Kyoto, Japan).
(*) E-mail address: [email protected]