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

Dubrovin, R. M. and Brulev, A. I. and Vovk, N. R. and Eliseyev, I. A. and Novikova, N. N. and Chernyshev, V. A. and Smirnov, A. N. and Davydov, V. Yu. and Wu, Anhua and Su, Liangbi and Mikhaylovskiy, R. V. and Kalashnikova, A. M. and Pisarev, R. V. (2025) Spin and lattice dynamics at the spin-reorientation transitions in the rare-earth orthoferrite Sm 0.55 Tb 0.45 FeO 3. Physical Review B, 112 (17): 174419. ISSN 2469-9950

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Abstract

Linear and nonlinear 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 Sm0.55⁢Tb0.45⁢FeO3 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⁡(⁡) 1 ⇆ Γ24⁡(Gac⁡Fac) 2 ⇆ Γ2⁡(Gc⁡Fa) at 1≃220K and 2≃130K 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 Δ⁢=1−2≃90K in mixed Sm0.55⁢Tb0.45⁢FeO3 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 1⁢ 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.