Jahn-Teller Distortions Cooperating with Magnetic Interaction inthe Raman Spectra of La_0.75Ca_0.25MnO₃ Thin Film

Remarkable changes (additional peaks, frequency shift, and peak width) of Raman spectra of a La_0.75Ca_0.25MnO₃ thin film have been observed during the paramagnetic insulator-ferromagnetic metal transition. The v₁ band (230 cm^-1) hardens by lattice contraction as a result of the rearrangement of MnO₆ octahedra. The Jahn-Teller distortions seem to be responsible for the broadening of v₂ band (485 cm^-1) above the magnetic transition temperature T_C. It is proposed that the 438 cm^-1 vibration mode activated in the magnetic ordering state is associated with the rearrangement of MnO₆ octahedra. The softening of v₃ band (610 cm^-1) below T_C can be ascribed to the magnetic interaction that brings into spin-phonon coupling terms.