Nickel pair spectra in MgSiF6 ⋅ 6H2O

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Abstract
Low temperature EPR measurements have been made on single crystals of nickel doped MgSiF6 ⋅ 6H2O in the frequency ranges 23–25 and 34–36 GHz. The isolated Ni2+ ion and its satellite spectra were studied both for the ΔM = 0 and ΔM = 1 transitions with the external magnetic field parallel to the pseudotrigonal axis. Certain of the satellite lines in both transitions were fitted to a pair Hamiltonian containing an isotropic exchange term JS1 ⋅ S2 and a dipolar term, the contribution of the latter being calculated from the crystallographic data. The values g = 2.24±0.01, D = −(2.082±0.002) cm−1, ‖E‖ = (0.2195±0.0010) cm−1, and J = +(0.074±0.001) cm−1 were determined for parameters of the pair Hamiltonian at 4.2 K, while the spin Hamiltonian parameters for the isolated ion at 4.2 K were g = 2.24±0.005, D = −(2.16±0.01) cm−1, and ‖E‖ = (0.198±0.002) cm−1. 77 K parameters are reported for both spectra, and there is a discussion of the possible origins of the remaining ΔM = 0 satellite lines.