Ensembles of nitrogen-vacancy centers (NVCs) in diamond can be employed for sensitive magnetometry. In this work, we present a fiber-coupled NVC magnetometer with an unshielded sensitivity of $(30\pm 10)\mathrm{pT}/\sqrt{\mathrm{Hz}}$ in a (10–500)-Hz frequency range. This sensitivity is enabled by a relatively high green-to-red photon conversion efficiency, the use of a [100] bias-field alignment, microwave and lock-in amplifier (LIA) parameter optimization, as well as a balanced hyperfine-excitation scheme. Furthermore, a silicon carbide ($\mathrm{SiC}$) heat spreader is used for microwave delivery, alongside low-strain 1-${\mathrm{mm}}^3{}^{12}$$\mathrm{C}$ diamonds, one of which is placed in a second magnetically insensitive fluorescence-collecting sensor head for common-mode noise cancellation. The magnetometer is capable of detecting signals from sources such as a vacuum pump up to 2 m away, with some orientation dependence but no complete dead zones, demonstrating its potential for use in remote-sensing applications.

• Received 14 November 2022
• Accepted 13 February 2023

DOI:https://doi.org/10.1103/PhysRevApplied.19.044042