151Eu Mössbauer study of multiferroic Eu0.75Y0.25MnO3

We are herewith reporting the 151 Eu Mössbauer spectra collected on a polycrystalline powder sample of Eu 0.75 Y 0.25 MnO 3 from 15 K to room temperature. All the spectra consist of a single line, whose shape and related sample thickness are dependent on the temperature T . The thermal trend of the mean square displacement of Eu ion, obtained from the spectra analysis, clearly reveals a large low-temperature anharmonicity and in concomitance with the onset of the magnetic ordering consists in a linear strong decrease interrupted by two narrow wells at 29.5 K and 40 K. This behavior is interpreted in connection with the transfer of spectral weight from the 120 cm -1 optical phonon to the electromagnonic modes. The T -trend of the central shift shows that Eu 3+ electronic ground state in the magnetically ordered phase differs from the one in the paramagnetic state. Finally, the temperature dependence of the hyperfine field under T N gives a contribution to interpret some controversial features regarding the phase-diagram.