Abstract
In orthorhombic SmMn2O5 single crystals, Sm3+ crystal-field (CF) excitations are studied by infrared transmission as a function of temperature and under applied magnetic field up to 10 T. These measurements are complemented with the study of Raman-active phonon frequency shifts as a function of temperature between 300 and 5 K.
The frequencies of all H-6(j) crystal-field levels of Sm3+ were determined as well as those of H-6(j). At high temperatures, the evolutions of Sm3+ CF excitations exhibit anomalies around the characteristic temperatures, T* similar to 60 K and T-s similar to 120 K and reflect the thermal disorder induced by splitting of the Sm-O bonds in SmMn2O5 that contribute to the frequency and linewidth phonon shifting.
At low temperatures, the degeneracy of the ground-state Kramers doublet is lifted (Delta(0) similar to 36 cm(-1)) due to the Sm3(+)-Mn3+ interaction in the ferroelectric phase and strongly enhanced below T c similar to 26 K. The Sm-Mn exchange interaction J(6) is determined and compared to that of Gd-Mn interaction in GdMn2O5.
The Sm magnetic moment m(sm )(T) and the Sm contribution to the magnetic susceptibility are also evaluated from Delta(0)(T), indicating that the Sm-Mn interaction is strongly implicated in the magnetic and the ferroelectric orderings below similar to 26 K. The study of the Sm3+ CF excitations as a function of magnetic field reveals twinning in SmMn2O5.
This twinning could affect its electric polarization behavior versus magnetic field.