Effects of spin dynamics on photocarrier relaxation in multiferroic Eu_0.75Y_0.25MnO₃ revealed by optical pump-THz probe spectroscopy

Understanding and control of the antiferromagnetic order in multiferroic materials on an ultrafast time scales is a longstanding area of interest, due to its potential applications in magnetic data storage and ultrafast magnetoelectric switching. We present an optical pump-THz probe study of spin and photocarrier dynamics in multiferroic Eu_0.75Y_0.25MnO₃. We found a localized spin excitation, triggered by the ultrafast switching of superexchange interactions on Mn2+ and Mn4+ sites, that decayed within tens of picoseconds with strong temperature dependence. More interestingly, an acceleration of electron-hole recombination developed below the Neel temperature (47 K). This is likely due to enhanced recombination in the A-type AFM state, when the electron spins are aligned in the same plane, without hopping along c axis.  Additionally, after 1.5 eV excitation of d-d transitions, we did not observe any obvious changes in the electromagnon modes. Overall, the observed fundamental optomagnetic processes can shed light on ultrafast control of magnetism in multiferroics and photoinduced phase transitions.