Mössbauer Effect inIr193in Intermetallic Compounds and Salts of Iridium

Abstract

Recoilless-absorption measurements of the 73-keV $\ensuremath{\gamma}$ rays of ${\mathrm{Ir}}^{193}$ have been carried out using an ${\mathrm{Os}}^{193}$ source in metallic form and absorbers of Ir metal, ${\mathrm{Fe}}_{0.99}$${\mathrm{Ir}}_{0.01}$, various rare-earth-iridium ($R{\mathrm{Ir}}_{2}$) intermetallic compounds, and a few trivalent and tetravalent Ir salts. From the measurements, the assignment of spin \textonehalf{} to the 73-keV level was confirmed, and the ratio of the magnetic moment of this level to the magnetic moment of the ground level was found to be 3.0\ifmmode\pm\else\textpm\fi{}0.1. The small value obtained for the magnetic moment of the first excited state can be explained by the core-excitation model of de Shalit. The results yielded a value of ${\ensuremath{\delta}}^{2}=0.37\ifmmode\pm\else\textpm\fi{}0.06$ for the $\frac{E2}{M1}$ mixing ratio of the 73-keV transition. The absolute values of the internal magnetic fields acting on the Ir nuclei in iron and in the $R{\mathrm{Ir}}_{2}$ compounds were deduced. The dependence of these fields on the rare-earth element was found to follow approximately the predictions of the Kasuya-Yosida theory on conduction-electron polarization, though an exact fit between this theory and experiment was not obtained. The electric field gradients acting on the Ir nuclei in the hexagonal Os metal lattice, in some Ir salts, and in the various $R{\mathrm{Ir}}_{2}$ compounds were deduced. Isomer-shift measurements indicate that the sign of $\ensuremath{\Delta}〈{r}^{2}〉$, the difference in the mean-square charge radii between the first excited state and ground state of ${\mathrm{Ir}}^{193}$, is positive.