Probing the role of Nd3+ ions in the weak multiferroic character of NdMn2O5 by optical spectroscopies
Abstrakt
Raman and infrared spectroscopies are used as local probes to study the dynamics of the Nd-O bonds in the weakly multiferroic NdMn2O5 system. The temperature dependence of selected Raman excitations reveals the splitting of the Nd-O bonds in NdMn2O5.
The Nd3+ ion crystal field (CF) excitations in NdMn2O5 single crystals are studied by infrared transmission as a function of temperature, in the 1800 - 8000 cm(-1) range, and under an applied magnetic field up to 11 T. The frequencies of all I-4(j) CF levels of Nd3+ are determined.
We find that the degeneracy of the ground-state Kramers doublet is lifted (Delta(0) similar to 7.5 cm(-1)) due to the Nd3+ -Mn3+ interaction in the ferroelectric phase, below T-c similar to 28 K. The Nd3+ magnetic moment m(Nd) (T) and its contribution to the magnetic susceptibility and the specific heat are evaluated from Delta(0) (T) indicating that the Nd3+ ions are involved in the magnetic and the ferroelectric ordering observed below similar to 28 K.
The Zeeman splitting of the excited CF levels of the Nd3+ ions at low temperature is also analyzed.