Room temperature organic magnets derived from sp3 functionalized graphene

Jiří Tuček,Piotr Błoński,Kateřina Holá,Athanasios B Bourlinos,Klára Čépe,Radek Zbořil,František Karlický,Matúš Dubecký,Michal Otyepka,Juri Ugolotti,Aristides Bakandritsos,Václav Ranc

doi:10.1038/ncomms14525

Abstract

Materials based on metallic elements that have d orbitals and exhibit room temperature magnetism have been known for centuries and applied in a huge range of technologies. Development of room temperature carbon magnets containing exclusively sp orbitals is viewed as great challenge in chemistry, physics, spintronics and materials science. Here we describe a series of room temperature organic magnets prepared by a simple and controllable route based on the substitution of fluorine atoms in fluorographene with hydroxyl groups. Depending on the chemical composition (an F/OH ratio) and sp3 coverage, these new graphene derivatives show room temperature antiferromagnetic ordering, which has never been observed for any sp-based materials. Such 2D magnets undergo a transition to a ferromagnetic state at low temperatures, showing an extraordinarily high magnetic moment. The developed theoretical model addresses the origin of the room temperature magnetism in terms of sp2-conjugated diradical motifs embedded in an sp3 matrix and superexchange interactions via –OH functionalization.

Highlights

Materials based on metallic elements that have d orbitals and exhibit room temperature magnetism have been known for centuries and applied in a huge range of technologies
The overall chemical composition of G(OH)F sample was determined by X-ray photoelectron spectroscopy (XPS) analysis (Supplementary Fig. 1), revealing the average contents of oxygen, fluorine, carbon and nitrogen to be 6.1, 27.2, 65.4 and 1.3 at.%, respectively
The presence of oxygen, fluorine, carbon and nitrogen was inferred from energy-dispersive X-ray (EDX) spectrum measured for the G(OH)F sample (Supplementary Fig. 2)

Summary

Introduction

Materials based on metallic elements that have d orbitals and exhibit room temperature magnetism have been known for centuries and applied in a huge range of technologies. Hydroxofluorographenes with an appropriate composition (an F/OH ratio) exhibit antiferromagnetic ordering at room temperature, a magnetic behaviour not previously observed for any graphene derivative or sp-based material At low temperatures, these hydroxofluorographenes undergo a transition to a ferromagnetic state with one of the highest magnetization values reported among graphenebased material. Based on the set of experimental data and high throughput first principles calculations on a large number of atomic configurations with varying F/OH ratio, we establish that the unique magnetism is attributed to a network of functionalization-induced sp2-conjugated carbon diradical motifs embedded in an sp[3] matrix, and the ability of –OH groups to stabilize magnetically ordered state up to room temperature due to emergence of superexchange interactions. The suggested theoretical model for hydroxofluorographene system has a universal nature and covers both ‘diradical motifs-induced magnetism’ appearing at high sp[3] coverages and sustaining up to room temperature and ‘defect-induced magnetism’, which emerges at lower degrees of sp[3] functionalization with limited sustainability at higher temperatures

Methods

Results

Conclusion