Magnetic states of atomic vacancies in graphite probed by scanning tunneling microscopy

Hyo Won Kim,Hwansoo Suh,Sung Woo Hwang,Insu Jeon,Hyeokshin Kwon,JiYeon Ku,Young Kuk,Youngtek Oh,Jin-Wook Jung,Wonhee Ko,Yeonchoo Cho

doi:10.1063/5.0010466

Abstract

Intrinsic defects in graphitic materials, like vacancies and edges, have been expected to possess magnetic states from the many-body interaction of localized electrons. However, charge screening from graphite bulk carriers significantly reduces the localization effect and hinders the observation of those magnetic states. Here, we use an ultra-low-temperature scanning tunneling microscope with a high magnetic field to observe the magnetic states of atomic vacancies in graphite generated by ion sputtering. Scanning tunneling spectroscopy reveals localized states at the vacancies, which exhibit splitting at a certain magnetic field whose separation increases with the field strength. The transition is well described by the “Anderson model,” which describes the emergence of localized magnetic states inside the metallic reservoir through electron–electron interaction. The interaction strength is estimated to be between 1 meV and 3 meV, which is supported by the density functional theory calculation. The observation provides an important foundation for application of intrinsic defects to carbon-based spintronic devices.

Highlights

Carbon-based spintronics have gained large attention because of the long spin-coherence time of electrons from the weak spin– orbit interaction and the absence of a nuclear spin in the most abundant C12 nuclei.[1]
Scanning tunneling microscopy/spectroscopy (STM/S) has identified the atomic structure and localized states of vacancies in graphene and graphite;[5,6,7,8,9] vacancy states that are split into two spin-polarized states, which is the hallmark of a magnetic state, have not been observed
To identify the vacancies with the localized states, we employed STS to observe the characteristic dI/dV spectra, which are proportional to the local density of states (LDOS), with a peak at about the Fermi energy from the π-band vacancy state.[3,5,6,7,8,9]

Summary

Introduction

Carbon-based spintronics have gained large attention because of the long spin-coherence time of electrons from the weak spin– orbit interaction and the absence of a nuclear spin in the most abundant C12 nuclei.[1]. Recent studies into other defects such as edges[10] and adatoms[11] have revealed that the interaction between defects and the underlying substrate significantly affects the electronic state, and minimizing hybridization between them (e.g., by using an insulating substrate) is important for retaining the magnetic properties of the defects. Graphite can be considered as graphene on top of a graphite substrate weakly bound by van der Waals interaction, and this weak interaction preserves the electronic properties of vacancies better than other metal substrates, as evidenced by sharp vacancy states with an energy broadening of only a scitation.org/journal/adv few millielectronvolts.[5,6] Observation of the spin splitting of vacancy states, requires an extreme energy resolution (i.e., finer than the broadening which is typically in a millielectronvolt range), making operating temperatures lower than 1 K a necessity

Methods

Results

Conclusion