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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.
Highlights
Noise coming from paramagnetic impurities is a widespread phenomenon that is relevant to fields ranging from magnetometry to solid-state qubits [1,2]
We show that strong magnetic field gradients
We look at the spacing in the radial direction, since this direction has the largest magnetic field strength gradients, and the highest suppression of spin diffusion
Summary
Noise coming from paramagnetic impurities is a widespread phenomenon that is relevant to fields ranging from magnetometry to solid-state qubits [1,2]. Interaction with paramagnetic impurities is considered one of the main factors that induce decoherence of the N-V center [3]. This decoherence is faster for shallow N-V centers close to the surface and slower for N-V centers in the bulk of the diamond sample, because shallow N-V centers are under the influence of a layer of electron spins at the surface of the diamond [1,4]. We present a method to measure the impurity spin density, where the sensor is decoupled from the diamond sample. The method is transferable to a wide range of samples [6]
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