We report a femtosecond response in photoinduced magnetization rotation in the ferromagnetic semiconductor
GaMnAs, which allows for detection of a four-state magnetic memory at the femtosecond time scale. The
temporal profile of this cooperative magnetization rotation exhibits a discontinuity that reveals two distinct
temporal regimes, marked by the transition from a highly non-equilibrium, carrier-mediated regime within the
first 200 fs, to a thermal, lattice-heating picosecond regime.
We present the observation of ultrafast photo-enhancement of ferromagnetism in Mn-doped III-V semiconductor
GaMnAs via photoexcited transient carriers. Our time-resolved magneto-optical Kerr spectroscopy reveals
transient enhancement of the magnetization amplitude on a 100 ps time scale after initial sub-picosecond demagnetization.
The dynamic enhancement of the magnetic ordering shows a maximum below the Curie temperature
Tc and completely dominates the demagnetization at high temperatures approaching Tc. We attribute the
observed ultrafast collective ordering to the transiently enhanced hole-Mn p-d exchange interaction, leading in
particular to a correlation-induced maximum bellow Tc and transient increase of Tc. These results constitute
the evidence for non-thermal, cooperative spin manipulation in (III,Mn)Vs on the ultrafast time scale.
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