A Brillouin scattering study of La0.77Ca0.23MnO3 across the metal–insulator transition

Temperature-dependent Brillouin scattering studies have been carried out on La 0.77 Ca 0.23 MnO 3 across the paramagnetic insulator–ferromagnetic metal (I–M) transition ( K). The spectra show modes corresponding to a surface Rayleigh wave (SRW) and a high velocity pseudo-surface wave (HVPSAW) along with bulk acoustic waves (B1 and B2). The Brillouin shifts associated with the SRW and HVPSAW increase, whereas the B1 and B2 frequencies decrease, below T C . The temperature dependence of the SRW and HVPSAW modes is related to the increase in the elastic constant C 11 across the I–M transition. The decrease in frequency across the I–M transition of the bulk modes is understood to be due to enhanced self-energy corrections as a result of increased magnon–phonon interaction across the I–M transition. Correspondingly, these modes show a large increase in the full width at half maximum (FWHM) as the temperature decreases. We also observe a central peak whose width is maximum at T C .