Mössbauer Spectroscopy withNi61in Nickel—Transition-Metal Alloys and Nickel Compounds

Nuclear $\gamma$ resonance spectra have been observed with 67.4-keV $\gamma$ rays of ${}_{}{}^{61}{}_{}{}^{}\mathrm{Ni}$ in Cu-Ni, Co-Ni, and Fe-Ni alloy absorbers and in some nickel-compound absorbers. The source contained the parent isotope ${}_{}{}^{61}{}_{}{}^{}\mathrm{Co}$, produced by the reaction ${}_{}{}^{64}{}_{}{}^{}\mathrm{Ni}(p,\alpha ){}_{}{}^{61}{}_{}{}^{}\mathrm{Co}$, in a nonmagnetic ${}_{}{}^{64}{}_{}{}^{}\mathrm{Ni}_{0.86}^{}{}_{}{}^{}$ ${\mathrm{V}}_{0.14}$ alloy. Source and absorber were held at 4.2 °K. The magnetic moment of the 67.4-keV state of ${}_{}{}^{61}{}_{}{}^{}\mathrm{Ni}$, $\mu \mathrm{}\left(67.4\right)=(+0.481\mathrm{}\pm 0.006){\mu }_N$ was determined to a better precision than by earlier measurements. Limits were placed on the value of the fractional change in charge radius ${\left(\frac{\Delta R}{R}\right)}_N$ of the 67.4-keV state compared to the ground-state radius, $-1.8\mathrm{}\times {10}^{-4\mathrm{}}\le {\left(\frac{\Delta R}{R}\right)}_N\le -0.7\mathrm{}\times {10}^{-4\mathrm{}}$. The concentration dependence of the average magnetic hyperfine field at ${}_{}{}^{61}{}_{}{}^{}\mathrm{Ni}$ nuclei in Ni-Fe, Ni-Co, and in Ni-Cu alloys is very nearly proportional to that of the bulk alloy magnetization. Absolute values of the hyperfine field in antiferromagnetic ${\mathrm{Ni}}^{2+}$ compounds agree wtih the results of unrestricted Hartree-Fock calculations. We have deduced isomer shifts from the measured energy shifts after subtracting second-order Doppler-shift contributions. The results are compared with values of electron densities at ${}_{}{}^{61}{}_{}{}^{}\mathrm{Ni}$ nuclei obtained from relativistic Hartree-Slater-Latter calculations.