A Time-Resolved Optical Study of the Paramagnetic Dielectric–Ferromagnetic Metal Transition in La[sub 0.7]Ca[sub 0.3]MnO[sub 3].

The relaxation dynamics of charge carriers in an epitaxial La[sub 0.7]Ca[sub 0.3]MnO[sub 3] film was studied by the light reflection method with a femtosecond time resolution in a wide temperature range. The relaxation of time-resolved photoinduced reflections was shown to be two-component in the whole temperature range including the paramagnetic dielectric–ferromagnetic metal transition at T ≈ 150–160 K. The fast relaxation component had a maximum lifetime (τ ∼ 500 ps) in the transition region, and its contribution to relaxation increased as temperature decreased. The lifetime of the slow component was minimum (τ ∼ 15 fs) in the transition region. In addition, fast oscillations assigned to coherent phonons appeared in photoinduced responses at T < 200 K. The dephasing time of these oscillations increased as temperature decreased, whereas their frequency changed insignificantly. © 2003 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]