Electron Spin Resonance of Manganese in Borate Glasses

Abstract

The ESR spectra of Mn²⁺ ions have been observed in borate glasses of the composition (MnO)_x(B₂O₃+0.04 K₂O)_1−x with x from 0.001 up to 0.030. For small concentrations of Mn²⁺ the central fine‐structure transitions (M = +½↔—½), although broadened by the random orientation of small noncubic crystalline fields, show a well‐resolved hyperfine structure. In addition to the Δm=0 transitions, ``forbidden'' Δm=±1 have been observed. The spectra prove that the coordination of the O²⁻ ions around the Mn²⁺ ions is mainly cubic, but that small deformations of the cubic symmetry exist. The deformations vary from ion to ion, and range up to average values of the order of 5% in the interionic distances and 10 deg in the angles. The discussion has been based on a spin Hamiltonian involving an isotropic g factor, fine structure term D, and hyperfine structure term A. The line positions have been calculated up to the third order in D and A. The numerical results are: g=2.002±0.002, | A | /hc= (87–2)×10⁻⁴ cm⁻¹, and D_Av/hc= (89±10)×10⁻⁴ cm⁻¹, the latter value representing an average over all deviations from cubic symmetry.