Study of domain wall propagation in fept and fepd nanowires driven by sub-nanosecond pulse of magnetic field by micromagnetic simulation

In this study, we investigated the domain wall propagation behavior in FePt and FePd nanowires by micromagnetic simulation based on LLG equation. A rectangular shape nanowire model was generated with a fixed length of 2000 nm and varied thicknesses of 2.5 nm and 5 nm. The wire widths were varied of 50 nm, 100 nm, and 150 nm. The 500 ps length of magnetic-pulse was applied in-plane to a transverse type domain wall. We observed the Walker Breakdown field (H _WB), which means the maximum domain wall velocity before it was abruptly decreased. The transverse DW structure was maintained below H _WB while vortex/antivortex wall structure was formed in the higher magnetic field. Interestingly, the H _WB value of both FePt and FePd were decreased as the width and thickness of the nanowires increased. We have also analyzed the changing of the demagnetization and exchange energy for the domain wall structure transition from transverse wall to vortex/anti-vortex wall.