Study of spin-phonon interaction in multiferroic La_0.9Bi_0.1CrO₃ by Raman spectroscopy

Spin-phonon interaction is an interesting phenomenon that may find applications in spintronics, quantum information processing, etc. In multiferroic materials, spin-phonon interaction, if exists, may provide additional degrees of freedom that could lead to the development of novel technologies. Thus, investigating and understanding this interaction in a multiferroic material is of both fundamental and applied interests. Perovskite La_1-xBi_xCrO₃ is a mutiferroic material which turns from antiferromagnetic/antiferroelectric to ferromagnetic/ferroelectric with 10 % substitution of Bi³⁺ for La³⁺. Raman spectrum feature changes dramatically with 10 % substitution of Bi³⁺ for La³⁺ also, indicating a spin-phonon interaction. Furthermore, in La_0.9Bi_0.1CrO₃, the ∼700 cm⁻¹ mode is split into two Raman sub-modes. The intensity of the lower frequency (680 cm⁻¹) sub-mode starts increasing sharply around the Néel temperature T_N = 269 K upon cooling. Below T_N, the monotonic change in intensity reflects the magnetic exchange modulation, resulted from the interacting with the chromium atoms oscillation at the original Cr⁴⁺ position in LaCrO₃, related to the competing ferromagnetic and antiferromagnetic interactions, with the former prevailing at low temperatures. The interplay of magnetic exchange modulation interactions and chromium atoms oscillation (decreasing of the lower frequency sub-mode of the Bi³⁺ doping related John-Teller-like 700 cm⁻¹ mode) coincides with the corresponding magnetic phase transition (T_N), demonstrating a spin-phonon coupling in La_0.9Bi_0.1CrO₃ which may find applications in magnonic devices.