A new electron paramagnetic resonance center, in addition to the NE1 and NE2 centers, was identified. It was found in synthetic specimens which were grown from a Ni solvent and annealed at 2300K, was labelled RM1 and had S = ½. The RM1 spectrum appeared as a pattern of 9 lines, with an intensity distribution of roughly, 1:4:10:16:19:16:10:4:1, due to hyperfine interactions with 4 equivalent N nuclei. The RM1 center had C1h symmetry, and the anisotropic g-values: g1 = 2.1719, g2 = 2.052 and g3 = 2.042, and hyperfine values: A1/h = 31.8, A2/h = 26.4 and A3/h = 23.1MHz. It was proposed that the centre was possibly a Ni+ ion in a position midway between 2 adjacent vacancies, with 4 equivalent N atoms and 2 nearest-neighbor C atoms.

EPR of New Nickel-Nitrogen Center in Annealed Synthetic Diamond. R.I.Mashkovtsev, J.N.Palyanov: Solid State Communications, 1999, 111[7], 397-402