Magnetic-electronic pressure studies of natural iron-bearing minerals and materials using ⁵⁷Fe Mössbauer spectroscopy in a diamond anvil cell

The possibility of measuring ⁵⁷Fe Mössbauer spectra of natural isotopic abundance materials at variable high pressures and cryogenic temperatures in a diamond anvil cell (DAC) on a timescale comparable to conventional Mössbauer spectroscopy (MS) is described. This is exemplified by satisfactory spectra obtained for an ilmenite (FeTiO₃) sample (absorber) in ∼12 h at temperatures where the sample is paramagnetic and in 20-30 h below spin-ordering temperature of ∼60 K where resonance intensity is reduced due to magnetically split spectral components. A commercially available ⁵⁷Co(Rh) point source of 14.4 keV resonant radiation and a Kr-CO₂ proportional counter have both been used. Sufficiently high count-rates are obtained by using both the 14.4 keV resonant γ-ray and associated 1.8 keV escape peak events. To optimise the resonance effect, careful attention has been paid to minimize non-resonant radiation within the discriminator window set to select the 14.4 keV resonant radiation. This has been achieved by setting an appropriate source-DAC-detector geometry (i.e., solid angle) to reduce scattering events off components of the DAC to a minimum. By using conventional commercially available Mössbauer apparatus, magnetic-electronic properties of iron-bearing minerals and materials with an iron content greater than ∼20% may be investigated to pressures in excess of 10 GPa encompassing many minerals of the earth's interior.