Ultrafast Time Resolved Photoinduced Magnetization Rotation in a Ferromagnetic/Antiferromagnetic Exchange Coupled System

Ultrashort pulse laser techniques are applied to study optically induced modulation in exchange biased ferromagnetic/antiferromagnetic (FM/AF) thin bilayer films (NiFe/NiO). Photoexcitation of the FM/AF interface with subpicosecond laser pulses induces large modulation in the unidirectional exchange bias field ( $H_{\mathrm{ex}}$) on an ultrashort time scale. The “unpinning” of the exchange bias leads to coherent magnetization rotation in the permalloy film which is time resolved by the experiment and corresponds to a large modulation in the magnetization component ( $\Delta M_Z{/M}_S\sim 0.5$), on a time scale of 100 psec.