Magnetization Dynamics of Magnetic Nano-Elements on Ultrafast Time Scales.

Recently, our group has systematically studied the switching of a \textit{single} permalloy nano-disk (160 nm diameter) between the vortex and quasi-single domain ground states as a function of applied bias field, including the observation of real-time switching at particular fields [1]. This was performed using the time-resolved magneto-optical Kerr effect (TR-MOKE), which allows dynamics to be studied on sub-nanosecond time scales. To accurately simulate the switching behavior, it was necessary to take into account the domed shape of the nano-disks, which result from the lift-off fabrication. Because of the sensitivity of the magnetization dynamics to the shape of the disks, we have begun fabrication of nano-disks using a shadow mask procedure [2] with a collimated deposition source under ultra-high vacuum (UHV) to produce high quality nano-elements. Magnetization dynamics of these UHV fabricated nano-disks will be discussed, with complementary scanning probe microscopy characterization of the disks.\\ 1. Z. Liu, R.D. Sydora and M.R. Freeman, PRB \textbf{77}, 174410 (2008).\\ 2. M.M. Deshmukh, D.C. Ralph, M. Thomas and J. Silcox, Appl. Phys. Lett. \textbf{75}, 1631 (1999).