Spin relaxometry of single nitrogen-vacancy defects in diamond nanocrystals for magnetic noise sensing

TL;DR

This study investigates how the relaxation time of single NV centers in nanodiamonds varies with size and surface modifications, demonstrating their potential for nanoscale magnetic noise sensing and biological imaging.

Contribution

It provides the first detailed measurement of $T_1$ relaxation times in nanodiamonds of different sizes and shows surface Gd$^{3+}$ decoration effectively enhances magnetic noise detection capabilities.

Findings

$T_1$ decreases by three orders of magnitude from 100 nm to 10 nm nanodiamonds.

Gd$^{3+}$ surface decoration significantly quenches $T_1$, enabling magnetic noise sensing.

Single NV centers can detect approximately 14 electron spins within 10 seconds.

Abstract

We report an experimental study of the longitudinal relaxation time ($T_1$) of the electron spin associated with single nitrogen-vacancy (NV) defects hosted in nanodiamonds (ND). We first show that $T_1$ decreases over three orders of magnitude when the ND size is reduced from 100 to 10 nm owing to the interaction of the NV electron spin with a bath of paramagnetic centers lying on the ND surface. We next tune the magnetic environment by decorating the ND surface with Gd$^{3+}$ ions and observe an efficient $T_{1}$-quenching, which demonstrates magnetic noise sensing with a single electron spin. We estimate a sensitivity down to $\approx 14$ electron spins detected within 10 s, using a single NV defect hosted in a 10-nm-size ND. These results pave the way towards $T_1$-based nanoscale imaging of the spin density in biological samples.