Paramagnetic Resonance of S8 State Ions in Metals

A study of the electron paramagnetic resonance spectrum in several intermetallic compounds containing either europium or gadolinium has been made. These ions show very nearly the free ionic $g$ value in their paramagnetic spectra in ionic crystals, indicating that only small admixtures of higher states to the free ionic ground state are caused by the crystalline perturbation. In metals there is, however, a contribution to the ionic $g$ factor which can be attributed to the exchange interaction between the magnetic core and the conduction electrons. We have measured this contribution in ${\mathrm{GdAl}}_2$ . The effect was small and could only be identified after careful analysis of the observed line shapes and a correction for the magnetization of the samples. The sign of the exchange interaction is found to be negative, whereas such interactions are always positive in free ions. The interaction also gives rise to an indirect coupling with the other magnetic ions. The resonance lines are therefore exchange narrowed and of the Lorentz type. If other rare earths are substituted for some of the gadolinium, then an additional broadening is observed from which the s-f interaction for all rare earths can be estimated.