Widefield Quantum Sensor Images Vector Magnetic Fields of Micromagnetic Structures with Full Spatial Resolution

Understanding the intricate behaviour of magnetic fields within nanoscale devices is crucial for advancements in spintronics, magnetic memory, and even neuromorphic computing, yet comprehensively imaging these fields with both high resolution and full vector information presents a significant challenge. Orlando D. Cunha, Filipe Camarneiro, and João P. Silva, working at the International Iberian Nanotechnology Laboratory, alongside Hariharan Nhalil, Ariel Zaig, Lior Klein, and colleagues at Bar-Ilan University, now demonstrate a new approach to overcome this limitation. The team adapted a standard widefield microscope to create a camera-compatible system that uses nitrogen-vacancy centres in diamond to reconstruct the direction and strength of stray magnetic fields emanating from microfabricated structures. This innovative technique achieves a spatial resolution across a large field of view, with rapid acquisition times, establishing a practical and scalable method for routinely imaging the complex magnetic landscapes within advanced devices.

8 μT sensitivity. The sensor determines magnetic field strength and direction by measuring changes in the fluorescence emitted by the NV centres, which respond to magnetic fields through a phenomenon known as Zeeman splitting. By combining measurements taken with the diamond sample oriented in three different directions, the team achieved full vector field mapping. Researchers successfully imaged the stray fields emanating from a 200nm wide permalloy microwire and a 5μm wide magnetic vortex, demonstrating the sensor’s capabilities. This new technique offers a significant improvement in both imaging speed and sensitivity compared to existing methods, opening up new possibilities for characterising micromagnetic structures and devices. Its compact size and ease of operation make it suitable for a wide range of applications, including materials science, biomedicine, and non-destructive testing.

Many advanced technologies, including spintronics, magnetic memory, and neuromorphic computing, rely on spatially varying magnetic fields. Accurately imaging these fields with full vector information over large areas remains a significant challenge. Quantum sensing with NV centres in diamond offers a promising solution, but a practical, camera-based implementation for vector magnetometry on relevant microstructures had not been demonstrated. The team adapted a commercial widefield microscope to implement a pulsed optically detected magnetic resonance protocol, overcoming this limitation.

Diamond Microscope Resolution Limited by Noise

This research investigates the practical limits to spatial resolution achievable with a Quantum Diamond Microscope (QDM) used for magnetic imaging. While theoretical limits exist, this work focuses on the factors that actually constrain resolution in real-world experiments. The key finding is that the primary limitation isn’t the NV centre itself, but rather the diffraction limit imposed by the wavelength of the microwave radiation used to interrogate the NV centres. This means that even with perfect NV centres and optics, the achievable resolution is fundamentally limited by the microwave wavelength.

This finding is crucial because it guides future efforts to improve QDM resolution. It suggests that focusing on shorter wavelength microwave techniques, such as using higher frequency sources or near-field techniques, is the most promising path forward, rather than solely improving NV centre properties or optical collection. Quantum Diamond Microscopy (QDM) utilises NV centres in diamond as nanoscale magnetic field sensors, possessing spin properties sensitive to magnetic fields detectable optically. QDM offers the potential for high-resolution, non-invasive magnetic imaging at the nanoscale.

Rapid 3D Vector Magnetometry of Microstructures

This research successfully demonstrates a new method for mapping stray magnetic fields produced by microfabricated structures. By adapting a standard widefield microscope and employing a pulsed optically detected magnetic resonance protocol, scientists achieved nanotesla sensitivity and rapid acquisition times when imaging these fields in three dimensions. The technique resolves the orientation of magnetic fields across an extended area, overcoming limitations associated with slower, nanoscale scanning methods. The demonstrated approach offers a scalable solution for spatially resolved vector magnetometry, enabling detailed characterisation of complex magnetic devices.

Researchers achieved consistent per-orientation sensitivities across the imaging area and generated vector maps within minutes. This advancement promises to facilitate investigations into diverse magnetic phenomena, including magnetic skyrmions, van der Waals magnets, and magnetization dynamics in emerging spintronic platforms. The authors suggest potential improvements through enhancements in optical collection, antenna design, and sensor interfacing, which could push performance into the picotesla range. Future work will focus on imaging magnetic vortex structures and studying the influence of external magnetic fields on their position. The compatibility of this technique with standard microscopy setups ensures both scalability and accessibility for researchers in both materials science and biology.