Electron paramagnetic resonance study of Fe3+ at M-1 position in forsterite

In an electron paramagnetic resonance study of a synthetic single crystal of forsterite, Mg2SiO4, one spectrum of Fe3+ with maximum local symmetry -1 was observed. This spectrum arises from Fe3+ substituted for Mg2+ at the M-1 position. The second-order constants of the spectrum are b(2)(0) = 0.184 cm(-1) and b(2)(2) = 0.1422 cm(-1). All the fourth-order spin-Hamiltonian constants are given: they are much larger than generally observed in silicates. The zero-field splitting of the EPR spectrum is larger than the energy of the hyperfrequency field in the Q band; this case is near the limit of possibility of calculating the fourth-order constants of the spin Hamiltonian. It is shown that the substitution of Fe3+ for Mg2+ does not strongly modify the local structure and that there is no local charge compensation.