Paramagnetic Resonance ofS-State Ions in Metals of High Paramagnetic Susceptibility

The paramagnetic resonance of ${\mathrm{Gd}}^{3+}$ in metals shows $g$ shifts with respect to the free ionic $g$ value which are due to the valence-electron polarization in metallic hosts, and the effective exchange interaction of ${\mathrm{Cd}}^{3+}$ with these valence electrons. These shifts have been studied in metals and intermetallic compounds with high paramagnetic susceptibility such as Pd, ${\mathrm{Ni}}_5$Y, and ${\mathrm{Pd}}_3$U and in many alloys involving these metals and compounds. The effective exchange interaction is found to be generally much smaller than expected from the atomic spectra. It is negative for valence bands of $d$ character and positive in valence bands of $5f$ and $s$ character, and is therefore not the result of simple atomic exchange only. The shape of the Gd resonance lines gives information on the spatial variations in the valence-electron polarization of the host metals. Thus, it was found that Pd alloyed with La or H segregates into two phases. The valence-electron polarization can be altered by admixture of other magnetic ions, and it was therefore possible to measure the exchange interaction for many rare earths and Fe, Co, Ni in Pd, and some rare earths in ${\mathrm{Ni}}_5$Y. The Gd line shape in these experiments allowed a study of the nonlocal character of the valence-electron susceptibility, and it appears that in Pd and in ${\mathrm{Ni}}_5$Y this susceptibility has a larger range than predicted by the free-electron calculation of Ruderman-Kittel-Yosida.