Raman Scattering from Magnon Excitations in RFeO₃

Abstract

Raman scattering from one- and two-magnon excitations in various rare-earth orthoferrites are studied. The magnetic in-plane and out-of-plane anisotropy energies of these systems are obtained and discussed based on the two-sublattice model of ironspins. Detailed temperature dependence of the frequencies of two k≅0 magnons are also examined on YFeO₃, ErFeO₃, SmFeO₃, Er_0.7Sm_0.3 FeO₃ and DyFeO₃. It is shown that the softening behaviors of one-magnon peak frequencies are different between the rotational- and abrupt-type spin-reorientation (SR) systems. This is explained by different anisotropy terms which contribute to the magnon softening associated with SR transitions. The exchange interactions between the iron and rare-earth ions are considered to interpret the magnon softening in the vicinity of SR temperatures. The temperature and polarization properties of two-magnon Raman spectra are also discussed.