Ultrafast time resolved photoinduced magnetization rotation in a ferromagnetic/antiferromagnetic exchange coupled system

Ultrashort pulse laser techniques are applied to study optically induced mo dulation in exchange biased ferromagnetic/antiferromagnetic (FM/AF) thin bi layer films (NiFe/NiO). Photoexcitation of the FM/AF interface with subpico second laser pulses induces large modulation in the unidirectional exchange bias field (H-ex) on an ultrashort time scale. The "unpinning" of the exch ange bias leads to coherent magnetization rotation in the permalloy film wh ich is time resolved by the experiment and corresponds to a large modulatio n in the magnetization component (Delta M-Z/M-S similar to 0.5), on a time scale of 100 psec. [S0031-9007(99)09042-0].