Atomic-scale sensing of the magnetic dipolar field from single atoms

Abstract

Spin resonance provides the high-energy resolution needed to determine biological and material structures by sensing weak magnetic interactions. In recent years, there have been notable achievements in detecting and coherently controlling individual atomic-scale spin centres for sensitive local magnetometry. However, positioning the spin sensor and characterizing spin-spin interactions with sub-nanometre precision have remained outstanding challenges. Here, we use individual Fe atoms as an electron spin resonance (ESR) sensor in a scanning tunnelling microscope to measure the magnetic field emanating from nearby spins with atomic-scale precision. On artificially built assemblies of magnetic atoms (Fe and Co) on a magnesium oxide surface, we measure that the interaction energy between the ESR sensor and an adatom shows an inverse-cube distance dependence (r). This demonstrates that the atoms are predominantly coupled by the magnetic dipole-dipole interaction, which, according to our observations, dominates for atom separations greater than 1 nm. This dipolar sensor can determine the magnetic moments of individual adatoms with high accuracy. The achieved atomic-scale spatial resolution in remote sensing of spins may ultimately allow the structural imaging of individual magnetic molecules, nanostructures and spin-labelled biomolecules.

Engineering the Eigenstates of Coupled Spin- 1/2 Atoms on a Surface

“…2(d)] also yields the moment μTi = γћ/2 = 0.99 ± 0.11 μB [19], consistent with the moment of a free electron. A two-dimensional map of the fitted coupling strength [ Fig.…”

“…Using STM, exchange interactions have been determined by tunneling spectroscopy [7,15], magnetization curves [10,16] and relaxation times [17]. The recent introduction of single-atom ESR [18] increased the energy sensitivity sufficiently to allow measurements of the relatively weak, long-range dipolar interactions between high-spin magnetic atoms on a surface [12,19].…”

“…2(b), bottom panels], corresponding to the two thermally occupied spin states of the coupled atom [19]. The splitting between the peaks Δf = (J + 2D)/ћ offers a precise measurement of the magnetic interaction strength, which strongly depends on the relative spatial positions of the atoms (Supplemental Section 7) [12,19,24]. At larger atom separations, the anisotropic dipolar coupling is dominant and can be tuned from antiferromagnetic (AFM) to ferromagnetic (FM) by positioning Ti atoms at different orientations.…”

Electrical spin manipulation in graphene nanostructures

“…With this approach, the application of an off-plane electric field significantly larger than in conventional field effect transistor geometries is possible. On the other hand, STM can be used to carry out electrically driven spin paramagnetic resonance of individual atoms [41][42][43] and coupled spin 1/2 atoms [44]. Therefore, the electrical manipulation of localized spin states in graphene seems within reach with state-of-the-art surface scanning probes.…”

An ultrahigh-vacuum cryostat for simultaneous scanning tunneling microscopy and magneto-transport measurements down to 400 mK

“…8 They provide time resolution down to 100 ps 9 or, if combined with pulsed lasers, down to 500 fs. 10 Recently, even the option of electron spin resonance experiments down to the single atom limit has been shown, 11 which opens the door towards ultrahighvacuum (UHV) based experiments of coherent dynamics on the atomic scale. Hence, the STM starts to bridge the field of surface science with its well-controlled sample preparation down to the atomic limit and the field of magnetotransport studies with its versatile tuning knobs controlling electron systems down to individual electrons.…”