Magneto-optical resonance in ferromagnetic gadolinium

The optical constants n and k of ferromagnetic and paramagnetic gadolinium have been measured, at various temperatures, from polarimetric measurements, in the low energy range 0.5 to 1.5 eV. For the ferromagnetic state, evidence of extra-optical conductivity is found near 0.69 eV and attributed to magnetic ordering. It confirms Miwa and Mackintosh predictions, assuming that new energy gaps are introduced in the conduction band through the s-f exchange interaction. From the experimental determination of the energy gap resulting from a splitting of the conduction band between spin up and spin down bands, we have deduced the effective s-f exchange energy J(q) = 1.58 × 10^-13 erg.