Ridene Mohamed, Najafi Ameneh, Flipse Kees
Molecular Materials and Nanosystems, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands.
Nanomaterials (Basel). 2019 Feb 8;9(2):228. doi: 10.3390/nano9020228.
The discovery of room-temperature ferromagnetism of hydrogenated epitaxial graphene on silicon carbide challenges for a fundamental understanding of this long-range phenomenon. Carbon allotropes with their dispersive electron states at the Fermi level and a small spin-orbit coupling are not an obvious candidate for ferromagnetism. Here we show that the origin of ferromagnetism in hydrogenated epitaxial graphene with a relatively high Curie temperature (>300 K) lies in the formation of curved specific carbon site regions in the graphene layer, induced by the underlying Si-dangling bonds and by the hydrogen bonding. Hydrogen adsorption is therefore more favourable at only one sublattice site, resulting in a localized state at the Fermi energy that can be attributed to a pseudo-Landau level splitting. This = 0 level forms a spin-polarized narrow band at the Fermi energy leading to a high Curie temperature and larger magnetic moment can be achieved due to the presence of Si dangling bonds underneath the hydrogenated graphene layer.
在碳化硅上氢化外延石墨烯中发现室温铁磁性，这对从根本上理解这种长程现象提出了挑战。费米能级处具有色散电子态且自旋轨道耦合较小的碳同素异形体，并非铁磁性的明显候选者。在此我们表明，具有相对较高居里温度（>300 K）的氢化外延石墨烯中铁磁性的起源，在于石墨烯层中由底层硅悬键和氢键诱导形成的特定弯曲碳位点区域。因此，氢吸附仅在一个亚晶格位点更有利，导致费米能处出现一个局域态，这可归因于赝朗道能级分裂。这个 = 0 能级在费米能处形成一个自旋极化窄带，导致居里温度较高，并且由于氢化石墨烯层下方存在硅悬键，可实现更大的磁矩。
