Ferromagnetism of a graphite nodule from the Canyon Diablo meteorite

Abstract

There are recent reports of weak ferromagnetism in graphite and synthetic carbon materials such as rhombohedral C(60) (ref. 4), as well as a theoretical prediction of a ferromagnetic instability in graphene sheets. With very small ferromagnetic signals, it is difficult to be certain that the origin is intrinsic, rather than due to minute concentrations of iron-rich impurities. Here we take a different experimental approach to study ferromagnetism in graphitic materials, by making use of meteoritic graphite, which is strongly ferromagnetic at room temperature. We examined ten samples of extraterrestrial graphite from a nodule in the Canyon Diablo meteorite. Graphite is the major phase in every sample, but there are minor amounts of magnetite, kamacite, akaganéite, and other phases. By analysing the phase composition of a series of samples, we find that these iron-rich minerals can only account for about two-thirds of the observed magnetization. The remainder is somehow associated with graphite, corresponding to an average magnetization of 0.05 Bohr magnetons per carbon atom. The magnetic ordering temperature is near 570 K. We suggest that the ferromagnetism is a magnetic proximity effect induced at the interface with magnetite or kamacite inclusions.

Defect-induced magnetism in SiC: Interplay between ferromagnetism and paramagnetism

“…However, minor amounts of magnetite, kamacite, etc, also appear in their graphite samples [2]. These secondary phases are responsible for about two-thirds of the observed magnetization and the remaining one-thirds is attributed to the graphite-nodule.…”

“…The last point was firstly proposed by Coey et al, who suggested to measure a bulk graphite-nodule to gain a large ferromagnetic signal [2]. However, minor amounts of magnetite, kamacite, etc, also appear in their graphite samples [2].…”

“…A fundamental question is whether materials containing only s or p electrons can be ferromagnetic. For nearly two decades, there have been various theoretical and experimental studies devoted to clarifying this question [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. It turns out that materials with completely filled 3d or 4f shells or with only s or p electrons can be ferromagnetic when they contain defects.…”

Local defects and ferromagnetism in graphene layers

“…A number of recent experiments suggest that pure graphite behaves as a highly correlated electron system [1]. In particular it shows a metalinsulator transition in magnetic fields and insulating behavior in the direction perpendicular to the planes in different samples [1,2,3,4,5,6,7,8]. Recent results show ferromagnetic behavior [9], enhanced by proton bombardment [10], what opens up a new way to the creation of organic magnets [11].…”

Ferromagnetic semiconductor single-wall carbon nanotubes

“…We found that by doping boron and nitrogen the semiconductor gap, E g , of a zigzag SWCNT could be control 8 . It is shown that vacancy could lead to electron spin polarization, hence a magnetic SWCNT 9,10 . But role of doping finite magnetic impurity concentration on a zigzag SWCNT is not challenged.…”