N. J. McLaughlin, S. Li, J. A. Brock, S. Zhang, H. Lu, M. Huang, Y. Xiao, J. Zhou, Y. Tserkovnyak, E. E. Fullerton, H. Wang, C. R. Du
ACS Nano (2023)
https://doi.org/10.1021/acsnano.3c1063
https://arxiv.org/abs/2311.12256

 

Abstract
Effective control and readout of qubits form the technical foundation of next-generation, transformative quantum information sciences and technologies. The nitrogen-vacancy (NV) center, an intrinsic three-level spin system, is naturally relevant in this context due to its excellent quantum coherence, high fidelity of operations, and remarkable functionality over a broad range of experimental conditions. It is an active contender for the development and implementation of cutting-edge quantum technologies. Here, we report magnetic domain wall motion driven local control and measurements of NV spin properties. By engineering the local magnetic field environment of an NV center via nanoscale reconfigurable domain wall motions, we show that NV photoluminescence, spin level energies, and coherence time can be reliably controlled and correlated to the magneto-transport response of a magnetic device. Our results highlight the electrically tunable dipole interaction between NV centers and nanoscale magnetic structures, providing an attractive platform to realize interactive information transfer between spin qubits and non-volatile magnetic memory in hybrid quantum spintronic systems.

S. Li, M. Huang, H. Lu, N. J. McLaughlin, Y. Xiao, J. Zhou, E. E. Fullerton, H. Chen, H. Wang, C. R. Du
Nano Lett. 23, 5326 (2023)
https://doi.org/10.1021/acs.nanolett.3c01523
https://doi.org/10.48550/arXiv.2305.11343

 

Abstract
Noncollinear antiferromagnets with novel magnetic orders, vanishingly small net magnetization, and exotic spin related properties hold enormous promise for developing next-generation, transformative spintronic applications. A major ongoing research focus of this community is to explore, control, and harness unconventional magnetic phases of this emergent material system to deliver state-of-the-art functionalities for modern microelectronics. Here we report direct imaging of magnetic domains of polycrystalline Mn₃Sn films, a prototypical noncollinear antiferromagnet, using nitrogen-vacancy-based single-spin scanning microscopy. Nanoscale evolution of local stray field patterns of Mn₃Sn samples are systematically investigated in response to external driving forces, revealing the characteristic “heterogeneous” magnetic switching behaviors in polycrystalline textured Mn₃Sn films. Our results contribute to a comprehensive understanding of inhomogeneous magnetic orders of noncollinear antiferromagnets, highlighting the potential of nitrogen-vacancy centers to study microscopic spin properties of a broad range of emergent condensed matter systems.

P. Welter, B. A. Josteinsson, S. Josephy, A. Wittmann, A. Morales, G. Puebla-​Hellmann, C. L. Degen
Phys. Rev. Applied 19, 034003 (2023)
http://dx.doi.org/10.1103/PhysRevApplied.19.034003
https://doi.org/10.48550/arXiv.2205.06579

 

Abstract
We demonstrate a spectrum demodulation technique allowing for rapid imaging in scanning nitrogen-vacancy center magnetometry. Our method relies on a periodic excitation of the electron spin resonance by wide-band frequency sweeps at a kilohertz rate combined with a phase-locked detection of the photoluminescence signal. The technique is robust against changes in spectrum shape and photoluminescence intensity, and is readily extended by a frequency feedback to enable real-time tracking of the spin resonance. Fast scanning magnetometry is especially useful for samples where the signal dynamic range is large, of order millitesla, such as for ferromagnets or ferrimagnets. We demonstrate our method by mapping stray fields above the model antiferromagnet α-Fe2O3 (hematite) at pixel rates of up to 100Hz and an image resolution exceeding one megapixel.

P. Welter,. Rhensius, A. Morales, M. S. Wornle, C.-H. Lambert, G. Puebla-Hellmann, P. Gambardella, C. L. Degen
Appl. Phys. Lett. 120, 074003 (2022)
https://doi.org/10.1063/5.0084910
https://doi.org/10.48550/arXiv.2201.06450

 

Abstract
Scanning magnetometry with nitrogen-vacancy (NV) centers in diamond has emerged as a powerful microscopy for studying weak stray field patterns with nanometer resolution. Due to the internal crystal anisotropy of the spin defect, however, external bias fields—critical for the study of magnetic materials—must be applied along specific spatial directions. In particular, the most common diamond probes made from {100}-cut diamond only support fields at an angle of θ=55° from the surface normal. In this paper, we report fabrication of scanning diamond probes from {110}-cut diamond where the spin anisotropy axis lies in the scan plane (⁠θ=90°⁠). We show that these probes retain their sensitivity in large in-plane fields and demonstrate scanning magnetometry of the domain pattern of Co–NiO films in applied fields up to 40 mT. Our work extends scanning NV magnetometry to the important class of materials that require large in-plane fields.

A. K. C. Tan, H. Jani, M. Högen, L. Stefan, C. Castelnovo, D. Braund, A. Geim, A. Mechnich, M. S. G. Feuer, H. S. Knowles, A. Ariando, P. G Radaelli, M. Atatüre
Nat. Mater. (2023)
https://doi.org/10.1038/s41563-023-01737-4

 

Abstract
Whirling topological textures play a key role in exotic phases of magnetic materials and are promising for logic and memory applications. In antiferromagnets, these textures exhibit enhanced stability and faster dynamics with respect to their ferromagnetic counterparts, but they are also difficult to study due to their vanishing net magnetic moment. One technique that meets the demand of highly sensitive vectorial magnetic field sensing with negligible backaction is diamond quantum magnetometry. Here we show that an archetypal antiferromagnet—haematite—hosts a rich tapestry of monopolar, dipolar and quadrupolar emergent magnetic charge distributions. The direct read-out of the previously inaccessible vorticity of an antiferromagnetic spin texture provides the crucial connection to its magnetic charge through a duality relation. Our work defines a paradigmatic class of magnetic systems to explore two-dimensional monopolar physics, and highlights the transformative role that diamond quantum magnetometry could play in exploring emergent phenomena in quantum materials.

M. Högen, R. Fujita, A. K. C. Tan, A. Geim, M. Pitts, Z. Li, Y. Guo, L. Stefan, T. Hesjedal, M. Atatüre
ACS Nano 17, 16879-16885 (2023)
https://doi.org/10.1021/acsnano.3c03825

 

Abstract
Engineering nontrivial spin textures in magnetic van der Waals materials is highly desirable for spintronic applications based on hybrid heterostructures. The recent observation of labyrinth and bubble domains in the near room-temperature ferromagnet Fe_5–xGeTe₂ down to a bilayer thickness was thus a significant advancement toward van der Waals-based many-body physics. However, the physical mechanism responsible for stabilizing these domains remains unclear and requires further investigation. Here, we combine cryogenic scanning diamond quantum magnetometry and field reversal techniques to elucidate the high-field propagation and nucleation of bubble domains in trilayer Fe_5–xGeTe₂. We provide evidence of pinning-induced nucleation of magnetic bubbles and further show an unexpectedly high layer-dependent coercive field. These measurements can be easily extended to a wide range of magnetic materials to provide valuable nanoscale insight into domain processes critical for spintronic applications.

Q. Guo, A. D'Addario, Y. Cheng, J. Kline, I. Gray, H. F. H. Cheung, F. Yang, K. C. Nowack, G. D. Fuchs
Phys. Rev. Materials 7, 064402 (2023)
https://doi.org/10.1103/PhysRevMaterials.7.064402
https://doi.org/10.48550/arXiv.2210.06233

 

Abstract
Electrical switching of Néel order in an antiferromagnetic insulator is desirable as a basis for memory applications. Unlike electrically driven switching of ferromagnetic order via spin-orbit torques, electrical switching of antiferromagnetic order remains poorly understood. Here we investigate the low-field magnetic properties of 30-nm-thick, c-axis-oriented α−Fe₂O₃ Hall devices using a diamond nitrogen-vacancy center scanning microscope. Using the canted moment of α−Fe₂O₃ as a magnetic handle on its Néel vector, we apply a saturating in-plane magnetic field to create a known initial state before letting the state relax in low field for magnetic imaging. We repeat this procedure for different in-plane orientations of the initialization field. We find that the magnetic field images are characterized by stronger magnetic textures for fields along [¯1¯120] and [11¯20], suggesting that despite the expected 3-fold magnetocrystalline anisotropy, our α−Fe₂O₃ thin films have an overall in-plane uniaxial anisotropy. We also study current-induced switching of the magnetic order in α−Fe₂O₃. We find that the fraction of the device that switches depends on the current pulse duration, amplitude, and direction relative to the initialization field.

A. K. C. Tan, H. Jani, M. Högen, L. Stefan, C. Castelnovo, D. Braund, A. Geim, M. S. G. Feuer, H. S. Knowles, A. Ariando, P. G. Radaelli, M. Atatüre
arXiv:2303.12125 (2023)
https://arxiv.org/abs/2303.12125

 

Abstract
Whirling topological textures play a key role in exotic phases of magnetic materials and offer promise for logic and memory applications. In antiferromagnets, these textures exhibit enhanced stability and faster dynamics with respect to ferromagnetic counterparts, but they are also difficult to study due to their vanishing net magnetic moment. One technique that meets the demand of highly sensitive vectorial magnetic field sensing with negligible backaction is diamond quantum magnetometry. Here, we show that the archetypal antiferromagnet, hematite, hosts a rich tapestry of monopolar, dipolar and quadrupolar emergent magnetic charge distributions. The direct readout of the previously inaccessible vorticity of an antiferromagnetic spin texture provides the crucial connection to its magnetic charge through a duality relation. Our work defines a novel paradigmatic class of magnetic systems to explore two-dimensional monopolar physics, and highlights the transformative role that diamond quantum magnetometry could play in exploring emergent phenomena in quantum materials.

W. S. Huxter, M. F. Sarott, M. Trassin, C. L. Degen
Nat. Phys. 19, 644–648 (2023)
https://doi.org/10.1038/s41567-022-01921-4

 

Abstract
The ability to sensitively image electric fields is important for understanding many nanoelectronic phenomena, including charge accumulation at surfaces and interfaces and field distributions in active electronic devices. A particularly exciting application is the visualization of domain patterns in ferroelectric and nanoferroic materials, owing to their potential in computing and data storage. Here, we use a scanning nitrogen-vacancy (NV) microscope, well known for its use in magnetometry, to image domain patterns in piezoelectric (Pb[Zr_0.2Ti_0.8]O₃) and improper ferroelectric (YMnO₃) materials through their electric fields. Electric field detection is enabled by measuring the Stark shift of the NV spin using a gradiometric detection scheme. Analysis of the electric field maps allows us to discriminate between different types of surface charge distributions, as well as to reconstruct maps of the three-dimensional electric field vector and charge density. The ability to measure both stray electric and magnetic fields under ambient conditions opens opportunities for the study of multiferroic and multifunctional materials and devices.

S. Ernst, P. J. Scheidegger, S. Diesch, L. Lorenzelli, C. L. Degen
Phys. Rev. Lett. 131, 086903 (2023)
https://doi.org/10.1103/PhysRevLett.131.086903
https://doi.org/10.48550/arXiv.2301.05091

 

Abstract
We report on measurements of the photoluminescence (PL) properties of single nitrogen-vacancy (NV) centers in diamond at temperatures between 4-300 K. We observe a strong reduction of the PL intensity and spin contrast between ca. 10-100 K that recovers to high levels below and above. Further, we find a rich dependence on magnetic bias field and crystal strain. We develop a comprehensive model based on spin mixing and orbital hopping in the electronic excited state that quantitatively explains the observations. Beyond a more complete understanding of the excited-state dynamics, our work provides a novel approach for probing electron-phonon interactions and a predictive tool for optimizing experimental conditions for quantum applications.

B. G. Simon, S. Kurdi, J. J. Carmiggelt, M. Borst, A. J. Katan, T. Van Der Sar
Nano Lett. 22, 9198 (2022)
https://doi.org/10.1021/acs.nanolett.2c02791

 

Abstract
Nitrogen-vacancy (NV) magnetometry is a new technique for imaging spin waves in magnetic materials. It detects spin waves by their microwave magnetic stray fields, which decay evanescently on the scale of the spin-wavelength. Here, we use nanoscale control of a single-NV sensor as a wavelength filter to characterize frequency-degenerate spin waves excited by a microstrip in a thin-film magnetic insulator. With the NV probe in contact with the magnet, we observe an incoherent mixture of thermal and microwave-driven spin waves. By retracting the tip, we progressively suppress the small-wavelength modes until a single coherent mode emerges from the mixture. In-contact scans at low drive power surprisingly show occupation of the entire isofrequency contour of the two-dimensional spin-wave dispersion despite our one-dimensional microstrip geometry. Our distance-tunable filter sheds light on the spin-wave band occupation under microwave excitation and opens opportunities for imaging magnon condensates and other coherent spin-wave modes.

S. Vélez, S. Ruiz-​Gómez, J. Schaab, E. Gradauskaite, M. S. Wörnle, P. Welter, B. J. Jacot, C. L. Degen, M. Trassin, M. Fiebig, P. Gambardella
Nat. Nanotechnol. 17, 834 (2022)
https://doi.org/10.1038/s41565-022-01144-x

 

Abstract
Magnetic skyrmions are compact chiral spin textures that exhibit a rich variety of topological phenomena and hold potential for the development of high-density memory devices and novel computing schemes driven by spin currents. Here, we demonstrate the room-temperature interfacial stabilization and current-driven control of skyrmion bubbles in the ferrimagnetic insulator Tm₃Fe₅O₁₂ coupled to Pt, showing the current-induced motion of individual skyrmion bubbles. The ferrimagnetic order of the crystal together with the interplay of spin–orbit torques and pinning determine the skyrmion dynamics in Tm₃Fe₅O₁₂ and result in a strong skyrmion Hall effect characterized by a negative deflection angle and hopping motion. Further, we show that the velocity and depinning threshold of the skyrmion bubbles can be modified by exchange coupling Tm₃Fe₅O₁₂ to an in-plane magnetized Y₃Fe₅O₁₂ layer, which distorts the spin texture of the skyrmions and leads to directional-dependent rectification of their dynamics. This effect, which is equivalent to a magnetic ratchet, is exploited to control the skyrmion flow in a racetrack-like device.

W. S. Huxter, M. L. Palm, M. L. Davis, P. Welter, C.-H. Lambert, M. Trassin, C. L. Degen
Nat. Commun. 13, 3761 (2022)
https://doi.org/10.1038/s41467-022-31454-6

 

Abstract
Quantum sensors based on spin defects in diamond have recently enabled detailed imaging of nanoscale magnetic patterns, such as chiral spin textures, two-dimensional ferromagnets, or superconducting vortices, based on a measurement of the static magnetic stray field. Here, we demonstrate a gradiometry technique that significantly enhances the measurement sensitivity of such static fields, leading to new opportunities in the imaging of weakly magnetic systems. Our method relies on the mechanical oscillation of a single nitrogen-vacancy center at the tip of a scanning diamond probe, which up-converts the local spatial gradients into ac magnetic fields enabling the use of sensitive ac quantum protocols. We show that gradiometry provides important advantages over static field imaging: (i) an order-of-magnitude better sensitivity, (ii) a more localized and sharper image, and (iii) a strong suppression of field drifts. We demonstrate the capabilities of gradiometry by imaging the nanotesla fields appearing above topographic defects and atomic steps in an antiferromagnet, direct currents in a graphene device, and para- and diamagnetic metals.

P. J. Scheidegger, S. Diesch, M. L. Palm, C. L. Degen
Appl. Phys. Lett. 120, 224001 (2022)
https://doi.org/10.1063/5.0093548

 

Abstract
We report on the implementation of a scanning nitrogen-vacancy (NV) magnetometer in a dry dilution refrigerator. Using pulsed optically detected magnetic resonance combined with efficient microwave delivery through a co-planar waveguide, we reach a base temperature of 350 mK, limited by experimental heat load and thermalization of the probe. We demonstrate scanning NV magnetometry by imaging superconducting vortices in a 50-nm-thin aluminum microstructure. The sensitivity of our measurements is approximately 3 μT per square root Hz. Our work demonstrates the feasibility for performing noninvasive magnetic field imaging with scanning NV centers at sub-Kelvin temperatures.

M. L. Palm, W. S. Huxter, P. Welter, S. Ernst, P. J. Scheidegger, S. Diesch, K. Chang, P. Rickhaus, T. Taniguchi, K. Wantanabe, K. Ensslin, C. L. Degen
Phys. Rev. Applied 17, 054008 (2022)
https://doi.org/10.1103/PhysRevApplied.17.054008
https://doi.org/10.48550/arXiv.2201.06934

 

Abstract
We report on nanometer magnetic imaging of two-dimensional current flow in bilayer graphene devices at room temperature. By combining dynamical modulation of the source-drain current with ac quantum sensing of a nitrogen-vacancy center in the diamond probe tip, we acquire magnetic field and current density maps with excellent sensitivities of 4.6 nT and 20nA/μm, respectively. The spatial resolution is 50–100 nm. We introduce a set of methods for increasing the technique’s dynamic range and for mitigating undesired back-action of magnetometry operation (scanning tip, laser and microwave pulses) on the electronic transport. Finally, we show that our imaging technique is able to resolve small variations in the current flow pattern in response to changes in the background potential. Our experiments demonstrate the feasibility for detecting and imaging subtle spatial features of nanoscale transport in two-dimensional materials and conductors.

Y. Lee, M. Lee, J. Jo, S. Lee, J.-W. Yoo, T. Choi, A. Heinrich, D. Lee
Curr. Appl. Phys. 34, 59-63 (2022)
https://doi.org/10.1016/j.cap.2021.12.001

 

Abstract
We demonstrate imaging current flow in a transport device by measuring the current-induced Oersted field. A diamond scanning magnetometer that hosts a single nitrogen-vacancy (NV) center at the tip apex is used to obtain the image. We fabricate a U-shape of Pt wire and study evolution of the Oersted field as the current continuously changes its direction along the wire. We find a good agreement between the obtained results and the simulated images based on the Biot-Savart law. In order to show the capability of imaging different field components, we perform the same experiment but with two different axes of the NV center. This work provides a novel imaging method of the current profile and can be applied to various transport experiments.

F. Kalhor, L.-P. Yang, L. Bauer, Z. Jacob
Phys. Rev. Research 3, 043007 (2021)
https://doi.org/10.1103/PhysRevResearch.3.043007

 

Abstract
Nitrogen-vacancy (NV) centers in diamond have emerged as promising room-temperature quantum sensors for probing condensed matter phenomena ranging from spin liquids, two-dimensional (2D) magnetic materials, and magnons to hydrodynamic flow of current. Here we propose and demonstrate that the nitrogen-vacancy center in diamond can be used as a quantum sensor for detecting the photonic spin density, the spatial distribution of light's spin angular momentum. We exploit a single spin qubit on an atomic force microscope tip to probe the spinning field of an incident Gaussian light beam. The spinning field of light induces an effective static magnetic field in the single spin qubit probe. We perform room-temperature sensing using Bloch sphere operations driven by a microwave field (XY8 protocol). This nanoscale quantum magnetometer can measure the local polarization of light in ultra-sub-wavelength volumes. We also put forth a rigorous theory of the experimentally measured phase change using the NV center Hamiltonian and perturbation theory involving only virtual photon transitions. The direct detection of the photonic spin density at the nanoscale using NV centers in diamond opens interesting quantum metrological avenues for studying exotic phases of photons, nanoscale properties of structured light as well as future on-chip applications in spin quantum electrodynamics. 

L. Stefan, A. K.C. Tan , B. Vindolet, M. Högen, D. Thian, H. Khume Tan , L. Rondin , H. S. Knowles , J.-F. Roch, A. Soumyanarayanan, M. Atatüre
Phys. Rev. Applied 16, 014054 (2021)
https://doi.org/10.1103/PhysRevApplied.16.014054
https://doi.org/10.48550/arXiv.2101.10331

 

Abstract
Scanning diamond magnetometers based on the optically detected magnetic resonance of the nitrogen-vacancy center offer very high sensitivity and noninvasive imaging capabilities when the stray fields emanating from ultrathin magnetic materials are sufficiently low (less than 10mT). Beyond this low-field regime, the optical signal quenches and a quantitative measurement is challenging. While the field-dependent photoluminescence from the nitrogen-vacancy center can still provide qualitative information on magnetic morphology, this operation regime remains unexplored, particularly for surface magnetization larger than approximately 3mA. Here, we introduce a multiangle reconstruction (MARE) that captures the full nanoscale domain morphology in all magnetic field regimes leading to photoluminescence quench. To demonstrate this, we use [Ir/Co/Pt]₁₄ multilayer films with surface magnetization an order of magnitude larger than previous reports. Our approach brings noninvasive nanoscale magnetic field imaging capability of the nitrogen-vacancy center to the study of a wider pool of magnetic materials and phenomena.

M. S. Wörnle, P. Welter, M. Giraldo, T. Lottermoser, M. Fiebig, P. Gambardella, C. L. Degen
Phys. Rev. B 103, 094426 (2021)
https://doi.org/10.1103/PhysRevB.103.094426
https://doi.org/10.48550/arXiv.2009.09015

 

Abstract
We resolve the domain-wall structure of the model antiferromagnet Cr₂O₃ using nanoscale scanning diamond magnetometry and second-harmonic-generation microscopy. We find that the 180° domain walls are predominantly Bloch-like, and can coexist with Néel walls in crystals with significant in-plane anisotropy. In the latter case, Néel walls that run perpendicular to a magnetic easy axis acquire a well-defined chirality. We further report quantitative measurement of the domain-wall width and surface magnetization. Our results provide fundamental input and an experimental methodology for the understanding of domain walls in pure, intrinsic antiferromagnets, which is relevant to achieve electrical control of domain-wall motion in antiferromagnetic compounds.

M. Lee, S. Jang, W. Jung, Y. Lee, T. Taniguchi, K. Watanabe, H.-R. Kim, H.-G. Park, G.-H. Lee, D. Lee
Appl. Phys. Lett. 118, 033101 (2021)
https://doi.org/10.1063/5.0037899

 

Abstract
We demonstrate two-dimensional mapping of current flow in graphene devices by using a single-spin scanning magnetometer based on a nitrogen-vacancy defect center in diamond. We first image the stray magnetic field generated by the current and then reconstruct the current density map from the field data. We focus on the visualization of current flow around a small sized current source of ∼500 nm diameter, which works as an effective point contact. In this paper, we study two types of point-contacted graphene devices and find that the overall current profiles agree with the expected behavior of electron flow in the diffusive transport regime. This work could offer a route to explore interesting carrier dynamics of graphene including ballistic and hydrodynamic transport regimes.

M. S. Wörnle, P. Welter, Z. Kašpar, K. Olejník, V. Novák, R. P. Campion, P. Wadley, T. Jungwirth, C. L. Degen, P. Gambardella
arXiv:1912.05287 (2019)
https://doi.org/10.48550/arXiv.1912.05287

 

Abstract
Electrical and optical pulsing allow for manipulating the order parameter and magnetoresistance of antiferromagnets, opening novel prospects for digital and analog data storage in spintronic devices. Recent experiments in CuMnAs have demonstrated giant resistive switching signals in single-layer antiferromagnetic films together with analog switching and relaxation characteristics relevant for neuromorphic computing. Here we report simultaneous electrical pulsing and scanning NV magnetometry of antiferromagnetic domains in CuMnAs performed using a pump-probe scheme. We observe a nano-scale fragmentation of the antiferromagnetic domains, which is controlled by the current amplitude and independent on the current direction. The fragmented antiferromagnetic state conserves a memory of the pristine domain pattern, towards which it relaxes. Domain fragmentation coexists with permanent switching due to the reorientation of the antiferromagnetic moments. Our simultaneous imaging and resistance measurements show a correlation between the antiferromagnetic domain fragmentation and the largest resistive switching signals in CuMnAs.

S. Vélez, J. Schaab, M. S. Wörnle, M. Müller, E. Gradauskaite, P. Welter, C. Gutgsell, C. Nistor, C. L. Degen, M. Trassin, M. Fiebig, P. Gambardella
Nat. Commun. 10, 4750 (2019)
https://doi.org/10.1038/s41467-019-12676-7

 

Abstract
Recent reports of current-induced switching of ferrimagnetic oxides coupled to heavy metals have opened prospects for implementing magnetic insulators into electrically addressable devices. However, the configuration and dynamics of magnetic domain walls driven by electrical currents in insulating oxides remain unexplored. Here we investigate the internal structure of the domain walls in Tm₃Fe₅O₁₂ (TmIG) and TmIG/Pt bilayers, and demonstrate their efficient manipulation by spin–orbit torques with velocities of up to 400 ms⁻¹ and minimal current threshold for domain wall flow of 5 × 10⁶ A cm⁻². Domain wall racetracks are defined by Pt current lines on continuous TmIG films, which allows for patterning the magnetic landscape of TmIG in a fast and reversible way. Scanning nitrogen-vacancy magnetometry reveals that the domain walls of TmIG thin films grown on Gd₃Sc₂Ga₃O₁₂ exhibit left-handed Néel chirality, changing to an intermediate Néel–Bloch configuration upon Pt deposition. These results indicate the presence of interfacial Dzyaloshinskii–Moriya interaction in magnetic garnets, opening the possibility to stabilize chiral spin textures in centrosymmetric magnetic insulators.

L. A. Völker, K. Herb, E. Janitz, C. L. Degen, J. M. Abendroth
J. Chem. Phys. 158, 161103 (2023)
https://doi.org/10.1063/5.0145466

 

Abstract
Photoexcitable donor–bridge–acceptor (D–B–A) molecules that support intramolecular charge transfer are ideal platforms to probe the influence of chiral induced spin selectivity (CISS) in electron transfer and resulting radical pairs. In particular, the extent to which CISS influences spin polarization or spin coherence in the initial state of spin-correlated radical pairs following charge transfer through a chiral bridge remains an open question. Here, we introduce a quantum sensing scheme to measure directly the hypothesized spin polarization in radical pairs using shallow nitrogen–vacancy (NV) centers in diamond at the single- to few-molecule level. Importantly, we highlight the perturbative nature of the electron spin–spin dipolar coupling within the radical pair and demonstrate how Lee–Goldburg decoupling can preserve spin polarization in D–B–A molecules for enantioselective detection by a single NV center. The proposed measurements will provide fresh insight into spin selectivity in electron transfer reactions.

J. M. Abendroth, K. Herb, E. Janitz, T. Zhu, L. A. Völker, C. L. Degen
Nano Lett. 22, 7294 (2022)
https://doi.org/10.1021/acs.nanolett.2c00533
https://doi.org/10.48550/arXiv.2202.03969

 

Abstract
Nuclear magnetic resonance (NMR) imaging with shallow nitrogen–vacancy (NV) centers in diamond offers an exciting route toward sensitive and localized chemical characterization at the nanoscale. Remarkable progress has been made to combat the degradation in coherence time and stability suffered by near-surface NV centers using suitable chemical surface termination. However, approaches that also enable robust control over adsorbed molecule density, orientation, and binding configuration are needed. We demonstrate a diamond surface preparation for mixed nitrogen- and oxygen-termination that simultaneously improves NV center coherence times for <10 nm-deep emitters and enables direct and recyclable chemical functionalization via amine-reactive cross-linking. Using this approach, we probe single NV centers embedded in nanopillar waveguides to perform ¹⁹F NMR sensing of covalently bound fluorinated molecules with detection on the order of 100 molecules. This work signifies an important step toward nuclear spin localization and structure interrogation at the single-molecule level.