Electron Paramagnetic Resonance Study of Ordered Mn2+ in Mg2SiO4

The electron paramagnetic resonance of Mn²⁺ in natural forsterite, both single crystal and powder, has been observed at 35 GHz. The spectrum is interpreted in terms of a spin Hamiltonian of orthorhombic symmetry with two equivalent sites related by a 67.5° rotation around the $c$ axis. Hence, the Mn²⁺ ions occupy either the $\text{M(1)}$ or the $\text{M(2)}$ positions in the crystal. Neither heat treatment nor proton irradiation showed disordering of the Mn²⁺ ions up to 600°C and 3 × 10¹⁷ protons/cm³, respectively.