2025/11/13 by Dubrovin, R. M., Brulev, A. I., Vovk, N. R. +10
#FOS: Physical sciences #Materials Science (cond-mat.mtrl-sci)
paper · doi:10.48550/arxiv.2511.10396
Linear and non-linear couplings of magnetic and lattice excitations are at the heart of many fascinating magnetophononic phenomena observed in rare-earth orthoferrites, the distinctive feature of which is the tendency to spin-reorientation transitions. Here we report the results of the experimental study of the spin and lattice dynamics in the Brillouin zone center of the rare-earth orthoferrite Sm0.55Tb0.45FeO3 by using polarized infrared reflectivity and Raman scattering spectroscopic techniques. The obtained results were supported by the first-principles calculations, which allowed us to reliably identify the parameters of most infrared- and Raman-active phonons. We reveal the spin-reorientation transitions Γ4(GaFc) \oversetT1\longleftrightarrow Γ24(GacFac) \oversetT2\longleftrightarrow Γ2(GcFa) at T1 ≃ 220 K and T2 ≃ 130 K and carefully studied the following evolution of Raman scattering on magnetic excitations at these transitions. Notably, the intermediate magnetic structure Γ24 displays an exceptionally broad temperature range ΔT = T1 - T2 ≃ 90 K in mixed Sm0.55Tb0.45FeO3 compared to pure rare-earth orthoferrites. We attribute this broadening of the intermediate phase to the modification of the magnetocrystalline anisotropy as a result of the inhomogeneous magnetic structure caused by the random distribution of rare-earth Sm3+ and Tb3+ ions. We found neither change in the parameters of Raman-active B1g phonons nor the appearance of new phonons induced by spin-reorientation transitions, which have been reported in SmFeO3. We assume that our results provide a solid basis for more deeper understanding of magnetophononic phenomena in rare-earth orthoferrites.