Spin and lattice dynamics at the spin-reorientation transitions in the rare-earth orthoferrite Sm$_{0.55}$Tb$_{0.45}$FeO$_{3}$

R. M. Dubrovin; A. I. Brulev; N. R. Vovk; I. A. Eliseyev; N. N. Novikova; V. A. Chernyshev; A. N. Smirnov; V. Yu. Davydov; Anhua Wu; Liangbi Su; R. V. Mikhaylovskiy; A. M. Kalashnikova; R. V. Pisarev

doi:10.1103/44m2-sq6k

paper

Spin and lattice dynamics at the spin-reorientation transitions in the rare-earth orthoferrite Sm $_{0.55}$ Tb $_{0.45}$ FeO $_{3}$

arXiv:2511.10396 · doi:10.1103/44m2-sq6k

Abstract

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 Sm $_{0.55}$ Tb $_{0.45}$ FeO $_{3}$ 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 $Γ_{4} (G_{a} F_{c}) ⟷ T_{1} Γ_{24} (G_{a c} F_{a c}) ⟷ T_{2} Γ_{2} (G_{c} F_{a})$ at $T_{1} ≃ 220$ K and $T_{2} ≃ 130$ K and carefully studied the following evolution of Raman scattering on magnetic excitations at these transitions. Notably, the intermediate magnetic structure $Γ_{24}$ displays an exceptionally broad temperature range $Δ T = T_{1} - T_{2} ≃ 90$ K in mixed Sm $_{0.55}$ Tb $_{0.45}$ FeO $_{3}$ 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 $Sm^{3 +}$ and $Tb^{3 +}$ ions. We found neither change in the parameters of Raman-active $B_{1 g}$ phonons nor the appearance of new phonons induced by spin-reorientation transitions, which have been reported in $SmFeO_{3}$ . We assume that our results provide a solid basis for more deeper understanding of magnetophononic phenomena in rare-earth orthoferrites.

15 pages, 8 figures, 5 tables

Spin and lattice dynamics at the spin-reorientation transitions in the rare-earth orthoferrite Sm0.55​Tb0.45​FeO3​

Abstract

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Spin and lattice dynamics at the spin-reorientation transitions in the rare-earth orthoferrite Sm $_{0.55}$ Tb $_{0.45}$ FeO $_{3}$