Probing phase separation in Nd1−xSrxMnO3 (x ≈ 0.4, 0.5) polycrystals through temperature dependent magnetic and Raman spectroscopy studies

Abstract

The manuscript reports temperature-dependent magnetic transitions correlated to variations in the phonon modes in Nd1−xSrxMnO3. Synthesis of x = 0.4 & 0.5 compounds by the solid-state reaction method was followed by structural/microstructural and electronic characterizations. The crystal structure of both compositions is orthorhombic with Pbnm symmetry, as confirmed by x-ray diffraction. The XPS data confirm the mixed Mn valance with the desired stoichiometry. The phase-separated nature is manifested through the occurrence of various phases, e.g., spin-glass (SG), charge order (CO), ferromagnetic (FM), and paramagnetic (PM), as the temperature is varied from 20 to 300 K. The temperature-dependent Raman measurements reveal that although the material is structurally stable in the studied temperature range of 80–440 K, noticeable discontinuities in the phonon mode shifts were noticed. These phonon mode shifts are found to directly correspond to the magnetic transitions. The change in the frequency of the Raman modes with temperature, which causes the observed shift, could be attributed to various factors such as lattice expansion, anharmonic interactions, spin-phonon coupling, electron-phonon interaction, etc. Here, we have used spin-phonon coupling along with lattice expansion as well as anharmonic interactions to describe the behavior of modes in the FM regime and lattice expansion and anharmonic interaction in the PM phase.