Multiple spin state analysis of magnetic nano graphene

TL;DR

This study investigates the spin states of asymmetric graphene molecules using density functional theory to understand the mechanism behind room-temperature ferromagnetism in graphite-like materials.

Contribution

It provides a detailed analysis of spin state stability in graphene molecules, revealing conditions for ferromagnetism relevant to spintronics and data storage applications.

Findings

Highest spin states are most stable in dihydrogenated zigzag edge molecules.

Lowest spin states are most stable in nitrogen-substituted molecules.

Room temperature ferromagnetism stability is linked to edge spins, exchange interactions, and atom positions.

Abstract

Recent experiments indicate room-temperature ferromagnetism in graphite-like materials. This paper offers multiple spin state analysis applied to asymmetric graphene molecule to find out mechanism of ferromagnetic nature. First principle density functional theory is applied to calculate spin density, energy and atom position depending on each spin state. Molecules with dihydrogenated zigzag edges like C64H27, C56H24, C64H25, C56H22 and C64H23 show that in every molecule the highest spin state is the most stable one with over 3000 K energy difference with next spin state. This result suggests a stability of room temperature ferromagnetism in these molecules. In contrast, nitrogen substituted molecules like C59N5H22, C52N4H20, C61N3H22, C54N2H20 and C63N1H22 show opposite result that the lowest spin state is the most stable. Magnetic stability of graphene molecule can be explained by three key issues, that is, edge specified localized spin density, parallel spins exchange interaction inside of a molecule and atom position optimization depending on spin state. Those results will be applied to design a carbon-base ferro-magnet, an ultra high density 100 tera bit /inch2 class information storage and spintronic devices.