Electron Spin Resonance in Cerium Metal

The electron-paramagnetic-resonance spectrum of pure polycrystalline metallic cerium was obtained at atmospheric pressure and at the temperatures 300, 196, and 77°K using a standard 1.25-cm microwave spectrometer in magnetic fields up to 26.5 kG. In order to interpret the results it is necessary to consider the effects of both the crystalline field and the exchange interactions which act on the $4f$ electrons. It is found that the cubic phase existing at atmospheric pressure and room temperature has a small trigonal distortion. In addition a series of satellite resonances are observed which are due to an indirect exchange interaction between ions having their $4f$ electrons in the different Stark levels produced by the crystalline field. Resonances were also observed from the hexagonal phase which coexists with the cubic phase at the temperatures investigated. The hexagonal-phase results agree with the predictions of crystal-field theory. The measured $g$ factors are: $g_{\mathrm{II}}=1.29\mathrm{}$, $g_{\perp }=1.07\mathrm{}$ for the -fcc phase (trigonal distortion); $g_{\mathrm{II}}=4.25\mathrm{}$, $g_{\perp }=0.6\mathrm{}$, and $g_{\mathrm{II}}=1.26\mathrm{}$, $g_{\perp }=2.14\mathrm{}$ for the -hexagonal phase. The $4f$ conduction-electron exchange energy for the fcc phase at 300°K is $\overline{I}=-0.062\mathrm{}$ eV.