# Unexpected Ferromagnetism--A Review
## 2 Examples of \(d^{0}\) Ferromagnetism
### Carbon Nanostructures
#### 2.3.3 Graphite  
The ferromagnetic behavior of graphitic materials has been strongly linked to lattice defects. For example, there have been studies on the irradiation-induced magnetism for graphite. Based on a comparison between the magnetic properties of the defects that are likely to be generated due to irradiation vacancies or H vacancy complexes, the results indicated that even though they are both magnetic, the adsorption of H greatly increases the magnetic moment [74]. Pure bulk graphite was investigated and showed ferromagnetic behavior attributed to the material's topographic defects [75]. Ion-implanted graphite is of extreme interest due to generating lattice defects, such as vacancies, in a controlled manner. Due to the unpaired electrons resulted from the ion beam, the induced defects could present magnetic moment. C\({}^{+}\) ion-implanted graphite was investigated in several studies. The results indicated that the exhibited ferromagnetism could mostly be attributed to the induced vacancy defects by implantation [76; 77]. Recent studies showed the generation of \"comet-like\" defects by swift heavy ions in highly ordered pyrolytic graphite. The analysis suggested that these types of defects have considerably higher magnetic signals in comparison to intrinsic surface defects [78]. [PERSON] et al. discuss the detection of FM in various highly crystalline graphite materials and the three main possible explanations for this behavior. The highest magnetization found was ~2.5 memu/g at room temperature with a high Curie transition Tc-900 K [79]. The magnetic impurities, such as as metallic iron or magnetite clusters, cannot be responsible for the observed magnetization due to higher Ms value measured (in some samples) towards those which would be provided by a magnetic impurity, doubled by the fact that the magnetic impurities should have a superparamagnetic and not a ferromagnetic behavior, as observed with HOPG samples. Thus, graphite samples magnetization remains practically temperature independent up to 800 K, contrasting with Fe superparamagnetic behavior, which sharply decreased with increasing temperature [79]. Topological defects, especially grain boundaries and edge states (the zig-zag edges), can induce an increase in DOS. If there is a high enough density of edge stated, it was considered that it can induce a ferrimagnetic spin polarization. Moreover, from theoretic data, it was suggested that a strong topological disorder will inhibit antiferromagnetic order while the ferromagnetic order will be enhanced [79]. Itinerant ferromagnetism can play a role in graphite FM, since this material has a low carrier density and the inter-electronic interaction is large in such \"dilute 2D electron gas systems\". Indirect evidence of this graphite electrons interactions was obtained from magnetoresistance analyses which revealed a \"field-induced metal-insulator-like transition\" [79]. Moreover, the powerful Coulomb interaction can lead to opening a gap in graphite Dirac fermions which is doubled by the detection of a weak magnetic moment induced by band anisotropy. Additionally, CESR (conduction electron spin resonance) measurements on HOPG and other highly crystalline graphite, such as Kish graphite, detected the presence of a ferromagnetic-like inner field. The authors underlined that the spin polarization and excitonic gap were induced by the Coulomb interaction even for the case when the magnetic field is absent. However, if a magnetic field is perpendicularly applied on the graphite sheets, even if the Coulomb interactions were weak, it can induce the gap formation [79]. The role of the defects in the graphite FM was also studied in [77]. Carbon ion implantation was used in the HOPG technique, which generated insulated and clustered vacancies. The room temperature (RT) FM in the irradiated graphite samples was directly correlated with the presence of generated vacancy defects.