Critical behavior of a photodisordered spin system in doped manganite

Abstract

Dynamics of the spin system has been investigated in a ferromagnetic ${\mathrm{La}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_{3}$ film by means of a time-resolved pump-probe method. In a weak excitation condition, the relaxation time $\ensuremath{\tau}$ increases critically on approaching the critical temperature ${T}_{\mathrm{C}}(=262$ K) from the low-temperature side as $\ensuremath{\tau}\ensuremath{\propto}|{T/T}_{\mathrm{C}}\ensuremath{-}1{|}^{\ensuremath{-}1.39}$ for $T\ensuremath{\gtrsim}200$ K. Surprisingly, the same scaling relation holds even after strong excitation in a much wider temperature range down to $\ensuremath{\sim}10$ K. We will discuss these behaviors in terms of photoinduced growth of the charge-ordering fluctuations.