Photoinduced 'transient thermoelectric effect (TTE)' in perovskite manganit
e La0.6Ca0.4MnO3 thin film has been measured under magnetic fields. The fas
t decay process of TTE signals is due to a recombination of photogenerated
electron-hole pairs through Mn4+ ions as capture centers, whose evaluated c
ross section sigma obeys the power law sigma proportional to T-1 (n = 0.75)
in the ferromagnetic phase far below T-c and in the paramagnetic phase. Fr
om the observed relaxation time tau (1), we evaluated the parameter ct char
acterizing a small polaron effect and the effective mass m*; both are enhan
ced appreciably near T-c. Such anomaly is attributed to the change in the t
hermal velocity of diffusing holes with downspin due to a small polaron eff
ect. (C) 2001 Published by Elsevier Science Ltd.