Critical behavior of a photodisordered spin system in doped manganite

Dynamics of the spin system has been investigated in a ferromagnetic La0.7Ca0.3MnO3 film by means of a time-resolved pump-probe method. In a weak excitation condition, the relaxation time tau increases critically on approaching the critical temperature T-C (=262 K) from the low-temperature side as tau proportional to \T/T-C - 1\(-1.39) for T greater than or similar to 200 K. Surprisingly, the same scaling relation holds even after strong excitation in a much wider temperature range down to similar to 10 K. We will discuss these behaviors in terms of photoinduced growth of the charge-ordering fluctuations.