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arXiv:2609.27097

Investigation of Widefield NV-Center Magnetic Imaging for Non-Destructive Materials Testing

Niklas Mathesa, Marvin Feuerhelm, Simon Philipp, Ivan Soldatov, Philipp DÁstolfo, Peter Knittel, Thomas Straubb, Jan Jeske, Rüdiger Quay, Xavier Vidal

physics.ins-detphysics.app-phquant-phSubmitted Sep 22, 2026• Announced Sep 24, 2026
v1 · Sep 22, 2026v2 · Sep 24, 2026
arXivHTMLPDF

Abstract

Due to progressing miniaturization, material fatigue is expected to gain importance on microscopic scales. Nevertheless, most non-destructive testing techniques are optimized for macroscopic scales. Therefore, new approaches applicable to miniaturized samples need to be explored. High spatial resolution imaging of a material's magnetic stray field enables sensitive detection of microstructural changes due to the local interplay of magnetic properties, strain, and defects. Up to now, this approach has rarely been used for materials testing since high-resolution magnetic sensing is traditionally challenging. Novel quantum sensing techniques offer the potential to close this gap. One of the most prominent quantum sensors, the nitrogen vacancy center in diamond, is investigated for non-destructive testing applications within the scope of this work. An experimental system based on a widefield sensing approach was developed to image magnetic stray field distributions within seconds to minutes over areas up to 1 x 1 $mm^2$. Magnetic sensitivities below 10 $μ$T/$\sqrt{\text{Hz}}$ and a spatial resolution of 1-2 $μ$m were achieved. The technique offers high mechanical stability, which is crucial for non-destructive testing applications. Comparison with magneto-optical Kerr effect measurements showed that the magnetic field maps are strongly correlated with the material's surface domains while containing additional information from deeper inside the sample. Characteristic changes in the magnetic stray field distribution were detected in an electrical steel sample after cyclic loading. A potential marker for early fatigue damage was deduced from the splitting gradient distribution, while 2D Fourier transform analysis provided additional insight.

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•Jan 1, 2018•0 citations
Due to progressing miniaturization, material fatigue is expected to gain importance on microscopic scales. Nevertheless, most non-destructive testing techniques are optimized for macroscopic scales. Therefore, new approaches applicable to miniaturized samples need to be explored. High spatial resolution imaging of a material's magnetic stray field enables sensitive detection of microstructural changes due to the local interplay of magnetic properties, strain, and defects. Up to now, this approach has rarely been used for materials testing since high-resolution magnetic sensing is traditionally challenging. Novel quantum sensing techniques offer the potential to close this gap. One of the most prominent quantum sensors, the nitrogen vacancy center in diamond, is investigated for non-destructive testing applications within the scope of this work. An experimental system based on a widefield sensing approach was developed to image magnetic stray field distributions within seconds to minutes over areas up to 1 x 1 mm2mm^2mm2. Magnetic sensitivities below 10 μμμT/Hz\sqrt{\text{Hz}}Hz​ and a spatial resolution of 1-2 μμμm were achieved. The technique offers high mechanical stability, which is crucial for non-destructive testing applications. Comparison with magneto-optical Kerr effect measurements showed that the magnetic field maps are strongly correlated with the material's surface domains while containing additional information from deeper inside the sample. Characteristic changes in the magnetic stray field distribution were detected in an electrical steel sample after cyclic loading. A potential marker for early fatigue damage was deduced from the splitting gradient distribution, while 2D Fourier transform analysis provided additional insight.
Many spintronic, magnetic-memory, and neuromorphic devices rely on spatially varying magnetic fields. Quantitatively imaging these fields with full vector information over extended areas remains a major challenge. Existing probes either offer nanoscale resolution at the cost of slow scanning, or widefield imaging with limited vector sensitivity or material constraints. Quantum sensing with nitrogen-vacancy (NV) centers in diamond promises to bridge this gap, but a practical camera-based vector magnetometry implementation on relevant microstructures has not been demonstrated. Here we adapt a commercial widefield microscope to implement a camera-compatible pulsed optically detected magnetic resonance protocol to reconstruct stray-field vectors from microscale devices. By resolving the Zeeman shifts of the four NV orientations, we reconstruct the stray-field vector generated by microfabricated permalloy structures that host multiple stable remanent states. Our implementation achieves a spatial resolution of ≈0.52 μm\approx 0.52 ~μ\mathrm{m}≈0.52 μm across an 83 μm×83 μm83~μ\mathrm{m} \times 83~μ\mathrm{m}83 μm×83 μm field of view and a peak sensitivity of $ (828 \pm 142)~\mathrm{nT\,Hz^{-1}}$, with acquisition times of only a few minutes. These results establish pulsed widefield NV magnetometry on standard microscopes as a practical and scalable tool for routine vector-resolved imaging of complex magnetic devices.
Quantum sensors harness the high sensitivity of quantum systems to external perturbations to accurately measure various physical quantities. Among the quantum systems employed for sensing purposes, the nitrogen-vacancy (NV) defect in diamond has garnered considerable attention as a magnetometer. A single NV center can be integrated in a scanning probe microscope to build a highly sensitive imaging tool which is particularly adapted to the investigation of antiferromagnets. Two approaches are possible, either the measurement of small static stray fields or the detection of magnetic noise.For canted antiferromagnetic textures, like the cycloidal state in multiferroic bismuth ferrite, the NV center can probe the stray field produced by the uncompensated moments, revealing the presence of topological defects in the magnetic order at the surface of bulk single crystals [1].Alternatively, thermally activated spin waves confined in domain walls generate a magnetic noise to which the NV center is also sensitive. This property allows the localization of the domain walls, which was demonstrated in synthetic antiferromagnets [2].Besides the NV centers, new sensors are emerging as magnetic field probes like the boron vacancies in h-BN, which offer the possibilty to integrate a sensing layer inside a van der Waals heterostructure [3].[1] Finco et al., Physical Review Letters, 128, 187201 (2022)[2] Finco et al., Nature Communications 12, 767 (2021)[3] Kumar et al., Physical Review Applied, 18, L061002 (2022)
In modern-day quantum metrology, quantum sensors are widely employed to detect weak magnetic fields or nanoscale signals. Quantum devices, exploiting quantum coherence, are inevitably connected to physical constants and can achieve accuracy, repeatability, and precision approaching fundamental limits. As a result, these sensors have shown utility in a wide range of research domains spanning both science and technology. A rapidly emerging quantum sensing platform employs atomic-scale defects in crystals. In particular, magnetometry using nitrogen-vacancy (NV) color centers in diamond has garnered increasing interest. NV systems possess a combination of remarkable properties, optical addressability, long coherence times, and biocompatibility. Sensors based on NV centers excel in spatial resolution and magnetic sensitivity. These diamond-based sensors promise comparable combination of high spatial resolution and magnetic sensitivity without cryogenic operation. The above properties of NV magnetometers promise increasingly integrated quantum measurement technology, as a result, they have been extensively developed with various protocols and find use in numerous applications spanning materials characterization, nuclear magnetic resonance (NMR), condensed matter physics, paleomagnetism, neuroscience and living systems biology, and industrial vector magnetometry. In this chapter, NV centers are explored for magnetic sensing in a number of contexts. In general, we introduce novel regimes for magnetic-field probes with NV ensembles. Specifically, NV centers are developed for sensitive magnetometers for applications where microwaves (MWs) are prohibitively invasive and operations need to be carried out under zero ambient magnetic field. The primary goal of our discussion is to improve the utility of these NV center-based magnetometers.
The recent decade has witnessed exciting developments in quantum science and technology. Quantum sensing is a rapidly growing branch, which exploits the fragility of quantum systems to detect small external signals. The extreme control at the single-atom level and the remarkably long coherence time of engineered quantum systems enable unprecedented sensitivity and precision, beating the performance of classical techniques. The nitrogen-vacancy (NV) center in diamond is one of the most promising quantum sensors. Its unique advantages have attracted considerable attention, including a long spin coherence time throughout a broad temperature range, nanoscale resolution limited by the sensor-sample distance, convenient optical control of its spin states and remarkably versatile sensing capabilities. Its properties are well studied under a bias magnetic field oriented along its quantization axis. However, its sensing capabilities in the presence of an off-axis magnetic field are much less explored. My research aims to unlock the full potential of NV quantum sensor by developing new sensing modalities under a magnetic field acting perpendicular to the NV axis, and furthermore, integrating them into a scanning probe microscope. In this dissertation, I will report our progress toward building a scanning NV multimodal quantum imaging platform, which will open up exciting opportunities in measuring nanoscale phenomena. The first chapter provides an introduction to the background of quantum sensing with NV centers, followed by a discussion on its basic properties and established sensing techniques. The second and third chapters are dedicated to two experiments performed under a perpendicular magnetic field where traditional NV magnetometry based on the Zeeman effect fails. In the second chapter, I will introduce a new sensing strategy that uses the entanglement between the electron and nuclear spins to restore the magnetic field sensitivity under this unfavored condition. This allows us to sense small changes in the magnetic field angle relative to the NV axis, and to detect anisotropic magnetic noise in the local environment. In the third chapter, I will present our latest development of scanning NV electrometry, where a single NV at the apex of a diamond scanning probe images external alternating (AC) and direct (DC) electric fields with sub-100 nm resolution. In the last chapter, I will discuss our efforts on four experiments that were left unfinished. I will present the results we have achieved, analyze the challenges that we faced and propose potential solutions to overcome them.
Solid-state spins in diamond are promising building blocks for quantum computing and quantum sensing, both of which require precise nanoscale addressing of individual spins. To explore the resolution limit of this approach, we demonstrate Fourier magnetic imaging of nitrogen-vacancy centers in diamond under state-of-the-art conditions. We constructed a highly compact experimental platform featuring thermal drift compensation under ambient conditions and generated a pulsed magnetic field gradient of up to 13.5 G/μμμm. By implementing the Fourier magnetic imaging protocol, we achieved localization of a single nitrogen-vacancy center with a spatial resolution of 0.28 ±\pm± 0.10 nm and a magnetic field measurement deviation of 9 nT. This technique holds potential for applications such as localizing spins within proteins and cells.
The NV defect center in diamond forms a pseudo-atomic quantum system with discreet optically excitable transitions between ground and excited states in the gap between valence and conduction bands, making the NV center a deep-level defect center in diamond. For the negatively charged NV center (NV-), both the ground and excited states are spin triplets (S=1) and coupling between optical and spin states provides unique opportunities for optical detection of magnetic resonance (ODMR) and quantum metrology under ambient conditions. As an atomically sized point defect that is stable in single nanodiamonds as small as a few nanometers, the NV center enables spin based imaging of temperature, electric fields, magnetic fields and mechanical strain with nanoscale spatial resolution. Made of carbon, nanodiamonds are also ideal nanoparticles for use in biological systems, exhibiting extremely low cytotoxicity, no photo bleaching and exceptional contrast in transmission electron and light microscopy. With the ability to act as both a passive, non perturbing sensor (e.g. a diamagnetic material used for sensing magnetic fields) and a connection point for two way, direct coupling of far field optics to NV−^-− spins and indirectly to the highly localized neighborhood of atoms, electronic states and phonon modes in the local vicinity, NV diamond provides a route to nanoscale field sensing and spin based optical microscopy. These sensors are also stable in nanodiamonds. For nanoparticles, the reduction in particle diameter dramatically enhances the proportion of the material that is surface exposed, enhancing any surface related properties. Nitrogen Vacancy centers in nanodiamonds provide another example of material properties that vary with particle size. In chapter 5, evidence that modulation of nanodiamonds fluorescent emissions by electrical perturbations in their surrouding environment allows transduction of local electrodynamics into a far field optical signal capable of mapping action potentials in cardiomyocytes in presented. The unifying theme for all of the work presented in this dissertation is to enable the use of magnetic resonance signals and interactions for imaging and sensing in previously inaccessible regimes. The specific focus is on methods and techniques to enable nanoscale physical sensing and functional imaging in live tissues, with the ultimate aim to lay the predicate for the combination of both without compromise.