Local structure studies of multiferroic RMn2O5 (R=Bi, Pr, Gd)

EXAFS measurements from 20 K to 300K were used to investigate the local structure of multiferroic RMn$_{2}$O$_{5}$ (R = Bi, Pr, Gd, TM~TC~40K) in transmission mode at the Mn K- and R L$_{3}$- edges in the XAFS2–LNLS beamline and analyzed using the IFEFFIT and FEFF codes. For BiMn$_{2}$O$_{5}$, Mn K-edge reveals very small temperature dependence of the Debye-Waller factor (DWF) and an Einstein temperature (ET) from Mn-O bonds of 675$\pm$22 K, suggesting that MnO polyhedra are rigid. We find structural distortions in the first coordination shell at the Bi L$_{3}$-edge associated to vibrational anomalies in the Bi-O bonds. The quantitative analysis relates the origin of such distortions to two very distinct values of DWT and ET (294$\pm$7K and 462$\pm$28K) for these bonds on first shell. Similar behavior is observed for PrMn$_{2}$O$_{5}$, and GdMn$_{2}$O$_{5}$.