Ultrafast optically induced spin dynamics in patterned single crystal Fe dot arrays

Optically induced ultrafast spin dynamics in nanoscale single crystal Fe dot arrays have been investigated using time-resolved magneto-optical Kerr effect (MOKE) pump-probe measurements. An ultrafast demagnetization process has been found to occur in the first 400 fs after the excitation with the femtosecond laser pulses for both the patterned dot arrays and the continuous film. While in the continuous Fe film the magnetization recovers monotonically with no precession, an optically induced spin precession has been observed in the patterned dot array with the precession frequency and the damping dependent on bias field strength. This result demonstrates that the modified magnetic anisotropies, as shown by the static focused MOKE measurements, in the patterned nanostructures can give rise to the optically induced spin precession.