Magnetic Properties of ion-implanted graphite and diamond
in collaboration with University of Leipzig , Divison of Superconductivity and Magnetism
Motivation:
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 (carbon atoms = black balls ) with one impurity atom (green) having a magnetic moment (red arrow) and one paramagnetic lattice defect (vacancy). |
Experiment:
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 of the depth profile of the Fe+-ion implanted into graphite |
Results:
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. |
