Spin-phonon coupling in orthorhombic RMnO3 (R=Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y):: A Raman study

The temperature-dependent Raman spectra of orthorhombic RMnO3 (R=Pr,Nd,Sm,Eu,Gd,Tb,Dy,Ho,Y) were studied in the 5-300 K temperature range. It was established that while the materials with large R3+ ionic radius r(R) and A-type antiferromagnetic order (R=Pr,Nd,Sm) exhibit significant phonon softening and other anomalies with decreasing temperature near and below T-N, the effect of magnetic ordering is much weaker or negligible in compounds with R=Eu, Gd, Tb, Dy, Ho, and Y, characterized by small r(R) and incommensurate magnetic structure. The results are discussed accounting for the variations with r(R) of the type of magnetic ordering and related spin-phonon interaction.