Time-resolved optical studies of spin and quasiparticle dynamics in colossal magnetoresistance materials: La0.67 Ca0.33 MnO3, La0.67 Sr0.33 MnO3, and Sr2 FeMoO6

We report on transient reflectivity and magneto-optical Kerr measurements from the colossal magnetoresistance compounds La0.67 Ca0.33 MnO3 (LCMO), La0.67 Sr0.33 MnO3 (LSMO), and Sr2 FeMoO6 (SFMO) as a function of temperature and magnetic field. In LCMO and LSMO, an unusually slow (∼1 μs) carrier relaxation component is revealed in the transient reflectivity traces. The component disappears as the transition temperature is approached from below. This slow decay process is attributed to spin-lattice relaxation of carriers in localized states and shows a close relationship with the spectral weight near the Fermi surface. The attribution is further supported by our pump-probe magneto-optical Kerr measurements. In addition to the clear observation of magnetic precessions, a long-lived exponentially decaying background reflects the spin-related relaxation of photoexcited electrons. In contrast to manganites, the temperature dependence of transient reflectivity is negligible, although there is a significant change in transient Kerr rotation in SFMO. Our results show that the dynamics of charge, spin, and lattice are strongly correlated with each other in the manganites, but the spin degree of freedom is thermally insulated from the electron and lattice systems.