Spin-dependent polaron formation dynamics in Eu0.75 Y0.25MnO3 probed by femtosecond pump-probe spectroscopy

We present a femtosecond optical pump-probe study of the multiferroic manganite Eu0.75Y0.25MnO3. The optical response of the material at pump energies of 1.55 and 3.1 eV is dominated by the d-d and p-d transitions of the Mn3+ ions. The relaxation of photoexcited electrons includes the relaxation of the Jahn-Teller distortion and polaron trapping at Mn2+ and Mn4+ sites. Ultrafast switching of superexchange interactions due to modulated eg orbital occupancy creates a localized spin excitation, which then decays on a time scale of tens of picoseconds at low temperatures. The localized spin state decay appears as a tremendous increase in the amplitude of the photoinduced reflectance, due to the strong coupling of optical transitions to the spin-spin correlations in the crystalline a-b plane.