There are more than 500 known color-centers in diamond . This is mostly thanks to the diamond industry, which took great care in characterizing them. For magnetic field sensing, only those defects whose effective spin is non-zero are of significance. If we model the defect as a single spin, , which couples to the magnetic field through its Zeeman interaction term, leading to the following, basic Hamiltonian:
Here D is the crystal field tensor, also known in the atomic physics community as zero-field splitting, and is the gyromagnetic ratio, which, for an isolated electron, is equal to 28.02 GHz/T.