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

The possibility of measuring Fe-57 Mossbauer spectra of natural isotopic ab undance materials at variable high pressures and cryogenic temperatures in a diamond anvil cell (DAC) on a timescale comparable to conventional Mossba uer spectroscopy (MS) is described. This is exemplified by satisfactory spe ctra obtained for an ilmenite (FeTiO3) sample (absorber) in similar to 12 h at temperatures where the sample is paramagnetic and in 20-30 h below spin -ordering temperature of similar to 60 K where resonance intensity is reduc ed due to magnetically split spectral components. A commercially available Co-57(Rh) point source of 14.4 keV resonant radiation and a Kr-CO2 proporti onal counter have both been used. Sufficiently high count-rates are obtaine d by using both the 14.4 keV resonant gamma -ray and associated 1.8 keV esc ape peak events. To optimise the resonance effect, careful attention has be en paid to minimize non-resonant radiation within the discriminator window set to select the 14.4 keV resonant radiation. This has been achieved by se tting an appropriate source-DAC-detector geometry (i.e., solid angle) to re duce scattering events off components of the DAC to a minimum. By using con ventional commercially available Mossbauer apparatus, magnetic-electronic p roperties of iron-bearing minerals and materials with an iron content great er than similar to 20% may be investigated to pressures in excess of 10 GPa encompassing many minerals of the earth's interior, (C) 2001 Elsevier Scie nce B.V. All rights reserved.