Mössbauer-Effect Measurements in Iron at High Pressures

Abstract

Six-line Mössbauer spectra were obtained for ${\mathrm{Fe}}^{57}$ in a natural iron-foil source over the pressure range 0 to 85 kbar, using a tetrahedral anvil press. An analysis of the data yielded the following results: The linewidth was not altered by pressure and was consistent with the ${\mathrm{Fe}}^{57}$ thickness of the source and absorber. The relative line intensities changed from 2.8: 2.4: 1.0: 1.0: 2.4: 2.8 at atmospheric pressure to 2.6: 1.3: 1.0: 1.0: 1.3: 2.6 at 80 kbar. This indicates that pressure polarized the iron foil so that the magnetic moments rotated out of the plane of the foil. This polarization was reversible. The isomer shift decreases linearly with pressure with a slope (-7.46±0.21) × ${10}^{-5\mathrm{}}$ cm ${\sec }^{-1\mathrm{}}$ ${\mathrm{kbar}}^{-1\mathrm{}}$. The effective magnetic field at the nucleus also decreased with pressure according to $\frac{\Delta H}{H_0}=(-1.34\mathrm{}\pm 0.25)\times {10}^{-4\mathrm{}}P-(0.60\mathrm{}\pm 0.39)\times {10}^{-6\mathrm{}}{P}^2$, with $P$ in kbar. A small quadrupole splitting was observed with the source under pressure, which increased as $\frac{\partial E_Q}{\partial P}=(0.96\mathrm{}\pm 0.23)\times {10}^{-5\mathrm{}}$ cm ${\sec }^{-1\mathrm{}}$ ${\mathrm{kbar}}^{-1\mathrm{}}$. The ratio of the splitting of the excited to the ground state was measured as $\frac{g_1}{g_0}=0.5714\mathrm{}\pm 0.0011$ and was independent of pressure. The absorption areas of the Mössbauer lines were measured, but attempts to calculate the $f$ factor indicate a possible variation of $f$ with polarization. Possible explanations are given for the polarization effect and quadrupole splitting.