Electron paramagnetic resonance of divalent nickel in ferrous fluosilicate

The EPR spectrum of Ni²⁺ in single crystals of ferrous fluosilicate FeSiF₆·6H₂O was studied at liquid helium temperatures in the frequency range 14.0–16.5 GHz. The six‐line spectrum, associated with six inequivalent Ni²⁺ sites, was fitted to the spin Hamiltonian $\mathrm{H}\mathrm{=\; g\beta }{\mathrm{H}}^{·}\mathrm{S}{\mathrm{\hspace{0.17em}+\hspace{0.17em}DS}}_z^2{\mathrm{+\; E\; (S}}_x^2{\mathrm{-\; S}}_y^2)$ , with S=1, g=2.255±0.005, D=−(3.05±0.02) cm⁻¹, and E=(0.170±0.001) cm⁻¹. The magnitudes of g and E and the sign of D were deduced, respectively, from the frequency dependence and the temperature dependence of the single line spectrum observed in the parallel orientation. The magnitude of D was obtained from measurements in the perpendicular plane. The perpendicular spectrum showed a sixfold rotational symmetry and consisted of two sets of three lines related by a rotation of (13.0±0.5)° about the c axis.