Magnetic Properties of ion-implanted graphite and diamond


in collaboration with  University of Leipzig , Divison of Superconductivity and Magnetism


Recently, weak ferromagnetism was discovered in graphite and predicted  in heavily doped diamond.  There is a controversial discussion about the origin of the ferromagnetism in carbon-based materials. Impurity or lattice defect mediated magnetism is under discussion. Ion implantation enables the introduction of impurity atoms and lattice defects in a well-controlled manner and, therefore, to study systematically the effect of impurities and defects on the magnetism.


Sketch of the basal plane of graphite

Sketch of the basal plane of graphite (carbon atoms = black balls ) with one impurity atom (green) having a magnetic moment (red arrow) and one paramagnetic lattice defect (vacancy).




Studied materials: highly oriented pyrolytic graphite (HOPG)

                                natural diamond (type IIa)
                                chemical vapor deposited (CVD) diamond

Implanted ions, ion energies, fluences, concentration  (at%)

iron (Fe),       1.0-4.0   MeV,   5.0x1014-2.0x1016 cm-2,  0.003 – 0.12
boron (B),      0.4-2.4   MeV,  2.3x1016-6.9x1016 cm-2,   0.5  - 1.5


Magnetization measurement with superconductive quantum interference device (SQUID)


Simulation depth profile

Simulation of the depth profile of the Fe+-ion implanted into graphite




high intrinsic diamagnetism

the paramagnetic component increases by ion implantation

- correlated wiht the implantation defects

- only small contribution from impurity moments

weak ferromagnetism

- no correlation with impurities

no ferromagnetism



Magnetization after subtraction of the linear part in units of 10-4 emu/g measured at T = 5 K as a function of the magnetic field for the iron implanted sample  in comparison with that of the virgin sample multiplied by a factor of three.