Diamond Quantum Sensing Microscopy of Magnetic Nanomaterials with Abdelghani Laraoui

Diamond quantum sensing microscopy based on nitrogen vacancy (NV) centers in diamond has become a powerful tool to detect weak magnetic fields with combined good spatial resolution (< 50 nm), magnetic sensitivity (pT/Hz^-1/2-mT/Hz^-1/2), and dynamic range (Hz-GHz), opening new doors to study nanoscale magnetic phenomena in low-dimensional materials [1-2]. First, I provide an overview of NV physics and describe some of the basic NV magnetometry protocols. Then, I discuss two recent studies using NV-based magnetic microscopy to study magnetic nanoparticles and van der Waals (vdW) magnets.
Superparamagnetic iron-oxide nanoparticles (SPIONs) are promising probes for biomedical imaging, but the heterogeneity of their magnetic properties is difficult to characterize with existing methods. Here, we perform wide-field imaging of the stray magnetic fields produced by hundreds of isolated ∼30 nm SPIONs using NV magnetic microscopy [3-4]. By analyzing the SPION magnetic field patterns as a function of applied magnetic field, we observe substantial field-dependent transverse magnetization components that are typically obscured with ensemble characterization methods. Most SPIONs exhibit a sharp Langevin saturation curve, enumerated by a characteristic polarizing applied field [5]. Using time-resolved NV magnetic microscopy, we directly record SPION Néel relaxation of hundreds of SPIONs [5]. Our time-resolved NV microscopy study reveals rich SPION sample heterogeneity and may be extended to other fundamental studies of nanomagnetism.
Chromium(III) chloride (CrCl₃), a layered vdW magnet, exhibits in-plane magnetic anisotropy and enhanced interlayer coupling upon stacking [6-7], making it an ideal platform to host exotic nanoscale magnetic phenomena such as magnon hydrodynamics [8]. Here, we investigate the spin dynamics of CrCl₃ nanoflakes using cryogenic NV microscopy, based on measuring optically detected magnetic resonance, Rabi oscillations, and spin–lattice relaxation time (T₁) of shallow NVs. In the ferromagnetic regime, we observe a pronounced reduction in the NV spin resonance contrast, a collapse of the Rabi oscillations, and a strong enhancement by 2 orders of magnitude of the relaxation rate Γ₁ = 1/T₁. These observations indicate intensified spin fluctuations in the gigahertz range [9]. Broadband ferromagnetic resonance spectroscopy on CrCl₃ crystals reveals resonance frequencies in the 4–15 GHz range together with a line width of ∼24 mT, further supporting the NV measurements [9]. These results are crucial for using CrCl₃ in 2D magnonics and hybrid quantum-magnon systems.

[1] F. Casola, et al., Nat. Rev. Mat. 3, 17088 (2018). [2] A. Laraoui, at al., App. Phys. Lett. 121, 060502 (2022). [3] I. Fescenko, et al., Phys. Rev. Appl. 11, 034029 (2019). [4] S. Lamichhane, et al., ACS Nano 17 (9), 8694-8704 (2023). [5] B. A. Richards, et al., ACS Nano 19 (10), 10048-10058 (2025). [6] A. Bedoya-Pinto, et al., Science 374 (6567), 616– 620 (2021). [7] J. Wang et al., Adv. Science 10 (3), 2203548 (2023). [8] R. Xue, et al., Science 392 (6800), 873–878 (2026). [9] B. Hammons, et al., ACS Nano 20 (29): 20776–20786 (2026).

This lecture was made possible by the William C. Ferguson Fund.