Relaxometry and dephasing imaging of superparamagnetic magnetite nanoparticles using a single qubit

TL;DR

This paper demonstrates a novel scanning probe technique using a nitrogen-vacancy center in diamond to study the magnetic dynamics of superparamagnetic nanoparticles, enabling characterization of nanoparticle size and behavior at the single-particle level.

Contribution

It introduces a method combining relaxometry and dephasing imaging with a single NV center to analyze magnetic nanoparticle dynamics and anisotropy effects.

Findings

Able to extract nanoparticle diameter and distance from NV center

Demonstrates anisotropy dependence of NV sensitivity

Potential for characterizing spin labels in medical and magnetic research

Abstract

To study the magnetic dynamics of superparamagnetic nanoparticles we use scanning probe relaxometry and dephasing of the nitrogen-vacancy (NV) center in diamond, characterizing the spin-noise of a single 10-nm magnetite particle. Additionally, we show the anisotropy of the NV sensitivity's dependence on the applied decoherence measurement method. By comparing the change in relaxation (T 1 ) and dephasing (T 2 ) time in the NV center when scanning a nanoparticle over it, we are able to extract the nanoparticle's diameter and distance from the NV center using an Ornstein-Uhlenbeck model for the nanoparticle's fluctuations. This scanning-probe technique can be used in the future to characterize different spin label substitutes for both medical applications and basic magnetic nanoparticle behavior.