MAGNETIZATION-DEPENDENT BEHAVIORS OF INTERBAND TRANSITIONS BETWEEN THE EXCHANGE-SPLIT BANDS IN DOPED MANGANITE FILMS

The temperature dependence of absorption spectra for thin films of double-exchange ferromagnet ${R}_{0.6}$Sr${}_{0.4}$MnO${}_{3}$ has been investigated with variation of the one-electron bandwidth $W$. With decreasing temperature, which corresponds to the increase of the magnetization $M$, a large amount of spectral weight transfers from the high- $(\ensuremath{\sim}$3 eV) to low- $(l~$1 eV) energy region. We ascribe these transitions to the interband transition between the bands split by the on-site exchange interaction $J$ and the intraband transition within the lower band, respectively. This suggests that optical excitations in the visible region strongly couple with local spin alignments in these doped manganites.