Low‐temperature X‐band EPR study of Mn2+‐, Cu2+‐, and Co2+‐doped NH4I single crystals

X‐band EPR of Mn2+,Cu2+, and Co2+ ions doped in ammonium iodide single crystals have been studied at low temperatures. The Mn2+ and Cu2+ spectra show the presence of only one type of complex for each with features similar to those observed at room temperature with no unusual changes. The results on Co2+ ion, reported here for the first time, reveal the presence of three equivalent Co2+ complexes having tetragonal symmetry with their tetragonal axes orthogonal to each other. The charge‐compensation mechanism and possible vacancy complexes are discussed, and the spin‐Hamiltonian parameters reported.