  Magnetic impurities in diamond influence the relaxation properties and thus
limit the sensitivity of magnetic, electric, strain, and temperature sensors
based on nitrogen-vacancy color centers. Diamond samples may exhibit
significant spatial variations in the impurity concentrations hindering the
quantitative analysis of relaxation pathways. Here, we present a local
measurement technique which can be used to determine the concentration of
various species of defects by utilizing double electron-electron resonance.
This method will help to improve the understanding of the physics underlying
spin relaxation and guide the development of diamond samples, as well as
offering protocols for optimized sensing.
