Lecture: Strategies to Magnetic Graphene towards Spintronic and Biomedical Applications

Abstract

Graphene, a single two-dimensional sheet of carbon atoms with an arrangement mimicking the honeycomb hexagonal architecture, has captured an immense interest of the scientific community since its isolation in 2004. Besides its extraordinarily high electrical conductivity and surface area, graphene shows a long spin lifetime and limited hyperfine interactions, which favors its potential exploitation in spintronic and biomedical applications, respectively, provided it can be made magnetic. However, pristine graphene is diamagnetic in nature due to solely sp² hybridization. Thus, various attempts have been proposed to imprint magnetic features into graphene. Following recent theoretical and experimental studies, it is believed that magnetic moments in graphene evolve only upon introduction of defects into the crystal lattice of graphene. The defects include local topology perturbations, point and line defects, vacancies, non-carbon atoms in the graphene lattice, adatoms, mixed sp²-sp³ hybridization resulting from chemical functionalization, and edges. The defect-induced magnetic moments must communicate with each other if a magnetic ordering is supposed to be established. However, there are doubts if the mediators of the magnetic interactions are sufficiently powerful to maintain the communication pathway and, hence, ensure self-sustainable magnetic ordering over the graphene lattice at relatively high temperatures.

Within the lecture, strategies involving doping of graphene lattice with non-carbon atoms and functionalization of graphene surface will be discussed with respect to the recent theoretical and experimental advancement in the quest for “magnetic” graphene. In particular, the issue of doping of graphene lattice with sulfur and nitrogen will be addressed in details highlighting the effect of the chemical nature and electronic character of the doping element, doping concentration, and doping-induced magnetic configurations on the magnetic properties of graphene.^1,2 A new magnetically active derivative of graphene, hydroxofluorographene, will be introduced as the first example of the organic graphene-based magnets with a magnetic ordering sustainable up to room temperature due to suitable sp3 functionalization.³ Experimental observations will be critically confronted with theoretical predictions, highlighting a significant role of the theoretical models for description and understanding of magnetic behavior of graphene-based materials.

References

1. Tucek, J.; Blonski, P.; Sofer, Z.; Simek, P.; Petr, M.; Pumera, M.; Otyepka, M.; Zboril, R. Sulfur Doping Induces Strong Ferromagnetic Ordering in Graphene: Effect of Concentration and Substitution Mechanism. Adv. Mater. 2016, 28, 5045-5053. DOI: 10.1002/adma.201600939
2. Blonski, P.; Tuček, J.; Sofer, Z.; Mazánek, V.; Petr, M.; Pumera, M.; Otyepka, M.; Zbořil, R. Doping with Graphitic Nitrogen Triggers Ferromagnetism in Graphene. J. Am. Chem. Soc. 2017, 139, 3171-3180, DOI: 10.1021/jacs.6b12934.
3. Tuček, J.; Holá, K.; Bourlinos, A. B.; Błoński, P.; Bakandritsos, A.; Ugolotti, J.; Dubecký, M.; Karlický, F.; Ranc, V.; Čépe, K.; Otyepka, M.; Zbořil, R. Room temperature organic magnets derived from sp3 functionalized graphene. Nat. Commun. 2017, 8, 14525, DOI: 10.1038/ncomms14525.