Very High Pressure Effects upon the EPR Spectrum of Ruby

Abstract

The variation in the electron paramagnetic resonance (EPR) spectrum of ruby as a function of pressure has been observed to beyond 70 kbar for a magnetic field orientation parallel to the crystalline c axis. The data can be interpreted in terms of the usual spin Hamiltonian: $\mathcal{H}{\mathrm{=g}}_{\mathrm{||}}{\mathrm{\beta H}}_z{S}_z-\frac{1}{2}{\mathrm{\delta (S}}_z^2-\frac{1}{3}{S}^2)$ , where the spectroscopic splitting factor g‖ has the same value as at ambient pressures, but where the zero‐field splitting δ increases in a linear fashion from ∼0.38 to ∼0.43 cm⁻¹. The experimental apparatus has been described previously, although important improvements in the pressure seal and in the pressure calibration have been made and are described in an Appendix.