Polarized Raman scattering and lattice eigenmodes of antiferromagnetic NdFeO3

Abstract

The first- and second-order Raman-active phonons in the orthorhombic Pbnm NdFeO3 single crystals were studied by means of polarized Raman scattering and lattice dynamics computations (LDC). The zone-center phonons of Ag symmetry were distinguished from the Big eigenmodes by performing polarized Raman scattering experiments using two parallel polarization configurations, X(ZZ)X' and Z(X'X)Z. With the help of LDC, we were able to assign most of the observed Raman-active modes, including phonons of B-2g and B-3g symmetry. The LDC results indicated that among the 16 force constants employed, the one corresponding to the stretching vibration between the central Fe cation and the axial oxygen atom in a FeO6 octahedron unit had the largest value. This suggests that the B-site Fe cation is more tightly bound to the axial O1 ion than the other two equatorial O-3 ions. It was further shown that at higher wavenumbers, the displacement of oxygen atoms contributed dominantly to the zone-center vibrations. Copyright (c) 2008 John Wiley & Sons, Ltd.