Magnetometry using Nitrogen-Vacancy (NV) color centers in diamond predominantly relies on microwave spectroscopy. However, microwaves may hinder certain studies involving biological systems or thin conductive samples. This work demonstrates a wide-field, microwave-free imaging magnetometer utilizing NV centers in nanodiamonds by exploiting the cross-relaxation feature near zero magnetic fields under ambient conditions without applying microwaves. For this purpose, we measure the center shift, contrast, and linewidth of the zero-field cross-relaxation in 140 nm nanodiamonds drop-cast on a current-carrying conductive pattern while scanning a background magnetic field, achieving a sensitivity of 4.5 μT/Hz. Our work allows for applying the NV zero-field feature in nanodiamonds for magnetic field sensing in the zero and low-field regimes and highlights the potential for microwave-free all-optical wide-field magnetometry based on nanodiamonds.
@article{arxiv.2409.02199,
title = {Microwave-free imaging magnetometry with nitrogen-vacancy centers in nanodiamonds at near-zero field},
author = {Saravanan Sengottuvel and Omkar Dhungel and Mariusz Mrózek and Arne Wickenbrock and Dmitry Budker and Wojciech Gawlik and Adam M. Wojciechowski},
journal= {arXiv preprint arXiv:2409.02199},
year = {2025}
}