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

We are herewith reporting the Eu-151 Mossbauer spectra collected on a polycrystalline powder sample of Eu0.75Y0.25MnO3 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 Eu3+ 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.