Density and $T_1$ of surface and bulk spins in diamond in high magnetic field gradients

TL;DR

This study measures surface and bulk spin densities in diamond using magnetic force microscopy under high magnetic field gradients, revealing insights into spin dynamics and potential applications across various materials.

Contribution

It introduces a novel measurement technique combining magnetic force microscopy with high field gradients to quantify spin densities and spin relaxation times in diamond.

Findings

Surface spin density of 0.072 spins/nm²

Bulk spin density of 0.4 ppm

Increase in T₁ time of surface spins in high gradients

Abstract

We report on surface and bulk spin density measurements of diamond, using ultra-sensitive magnetic force microscopy with magnetic field gradients up to 0.5 T/$\mu$m. At temperatures between 25 and 800 mK, we measure the shifts in the resonance frequency and quality factor of a cantilever with a micromagnet attached to it. A recently developed theoretical analysis allows us to extract a surface spin density of 0.072 spins/nm$^2$ and a bulk spin density of 0.4 ppm from this data. In addition, we find an increase of the $T_1$ time of the surface spins in high magnetic field gradients due to the suppression of spin diffusion. Our technique is applicable to a variety of samples other than diamond, and could be of interest for several research fields where surface, interface or impurity bulk spin densities are an important factor.