Competing exchanges and spin-phonon coupling in Eu1-xRxMnO3 (R=Y, Lu)

This work is focused on the phase diagrams and physical properties of Y-doped and Lu-doped EuMnO₃. The differences in the corresponding phase boundaries in the (x,T) phase diagram could be overcome by considering a scaling of the Y³⁺ and Lu³⁺ concentrations to the tolerance factor. This outcome evidences that the tolerance factor is in fact a more reliable representative of the lattice deformation induced by doping. The normalization of the phase boundaries using the tolerance factor corroborates previous theoretical outcomes regarding the key role of competitive FM and AFM exchanges in determining the phase diagrams of manganite perovskites. However, significant differences in the nature and number of phases at low temperatures and concentrations could not be explained by just considering the normalization to the tolerance factor. The vertical phase boundary observed just for Lu-doped EuMnO₃, close to 10% Lu, is understood by considering a low temperature Peierls-type spin-phonon coupling, which stabilizes the AFM-4 phase in Lu-doped EuMnO₃.