Unconventional and Exotic Magnetism in Carbon-Based Structures and Related Materials

Abstract

The detailed analysis of the problem of possible magnetic behavior of the carbon-based structures was fulfilled to elucidate and resolve (at least partially) some unclear issues. It was the purpose of the present paper to look somewhat more critically into some conjectures which have been made and to the peculiar and contradictory experimental results in this rather indistinct and disputable field. Firstly the basic physics of magnetism was briefly addressed. Then a few basic questions were thoroughly analyzed and critically reconsidered to elucidate the possible relevant mechanism (if any) which may be responsible for observed peculiarities of the "magnetic" behavior in these systems. The arguments supporting the existence of the intrinsic magnetism in carbon-based materials, including pure graphene were analyzed critically. It was concluded that recently published works have shown clearly that the results of the previous studies, where the "ferromagnetism" was detected in pure graphene, were incorrect. Rather, graphene is strongly diamagnetic, similar to graphite. Thus the possible traces of a quasi-magnetic behavior which some authors observed in their samples may be attributed rather to induced magnetism due to the impurities, defects, etc. On the basis of the present analysis the conclusion was made that the thorough and detailed experimental studies of these problems only may shed light on the very complicated problem of the magnetism of carbon-based materials. Lastly the peculiarities of the magnetic behavior of some related materials and the trends for future developments were mentioned.

Spinodal nanodecomposition in semiconductors doped with transition metals

“…As seen, the physics of high-T C ferromagnetism in magnetically doped oxides (Coey et al, 2010;Fukumura and Kawasaki, 2013;Li et al, 2012;Sawicki et al, 2013), carbon derivatives (Kuzemsky, 2013;Makarova, 2010;Wang et al, 2014), and some other systems (Nealon et al, 2012;Roever et al, 2011;Rylkov et al, 2012;Yao et al, 2012) is beyond the scope of this review. In particular, the question of ferromagnetism originating from spins residing on defects (Coey et al, 2010;Zhou, 2014) or on open p shells (Volnianska and Boguslawski, 2010), or mediated by defects or by residual impurities like hydrogen is not addressed here.…”

“…Finally, it is pointed out that spinodal nanodecomposition can be viewed as a new class of bottom-up approach to nanofabrication. The detection of ferromagnetic features persisting up to above room temperature in a variety of magnetically doped semiconductors and oxides has been one of the most surprising developments in materials science over recent years (Bonanni, 2007;Coey et al, 2010;Dietl, 2003;Fukumura and Kawasaki, 2013;Kobayashi et al, 2008;Kuzemsky, 2013;Liu et al, 2005;Makarova, 2010;Nealon et al, 2012;Pearton et al, 2003;Roever et al, 2011;Sawicki et al, 2013;Yao et al, 2012). In particular, the presence of robust ferromagnetism in technologyrelevant semiconductors (e.g., GaN and Si) and oxides (e.g., ZnO and TiO 2 ) has promised to open the door to a wide exploitation in devices of remarkable spintronic functionalities found in dilute ferromagnetic semiconductors [such as (Ga,Mn)As] below their Curie temperature T C , so far not exceeding 200 K (Dietl and Ohno, 2014;Jungwirth et al, 2014;Sato et al, 2010).…”

Prospects of spintronics based on 2D materials

“…Even though pristine single‐layer graphene is diamagnetic, intrinsic ferromagnetism in graphene has been predicted by numerous first‐principles calculations and measured experimentally, in the presence of defects, which can be created easily by irradiation or during growth process . As highlighted in recent reviews on carbon‐based structures, weak ferromagnetism reported by various authors in graphene is attributed to magnetism induced by impurities and defects. The localized electronic states due to dangling bonds around the defects contribute to the density of states (DOS) at the Fermi level which induce magnetism …”

Novel mechanism for weak magnetization with high Curie temperature observed in H-adsorption on graphene

“…on graphene and graphite has been experimentally observed above room temperature and predicted by calculations 1,2,21,35 . However, a convincing theory that explains these phenomena is still required 2, 19,21,[35][36][37][38][39] . Previously, we have explained 24,25 why Hund's rule does not hold when interpreting calculation results based on the singlet-electron approximation and the Bloch theorem in band theory.…”