Multi phonon resonance Raman scattering, spin phonon coupling and lattice dynamics of antiferromagnetic NdFeO$_{3}$

The Raman-active phonons in the orthorhombic NdFeO$_{3}$ single crystals were studied by means of polarized Raman scattering and lattice dynamics computations (LDC). The A$_{g}$-symmetry zone-center phonons were distinguished from the B$_{1g}$ eigenmodes by performing polarized Raman scattering experiments using two parallel polarization configurations, X$\prime $(ZZ)X$\prime $ and Z(X$\prime $X$\prime )$Z. Observed phonon spectra at 100, 300, 347 cm$^{-1}$ showed anomalous temperature dependence in the range of the magnetic spin reorientation temperature (100 --200K) indicating strong spin -phonon coupling. The anomalously shaped observed phonon between 500 to 1500 cm$^{{\-}1}_{, }$observed in the A$_{g}$-symmetry X$\prime $(ZZ)X$\prime $ and B$_{1g}$ spectrum was attributed to a multi-phonon scattering caused either by multiple combination of B$_{1g}$ or by A$_{1g }$phonons. With the help of lattice dynamics calculations, we were able to assign most of the observed Raman-active modes, including B$_{2g}$ and B$_{3g}$-symmetry phonons. The LDC results indicated that among the sixteen force constants employed, the force constant corresponding to the stretching vibration between the central Fe cation and the axial oxygen atom in a FeO$_{6}$ octahedron unit had the largest value.