Time-Resolved Spin Dynamics in Ferromagnetic Microstructures

This research program will study the spin dynamics of sub-micron ferromagnetic particles. Picosecond time-resolved Kerr microscopy will be used to study the excitation spectra and origins of spin dephasing in individual nanoparticles with simple magnetic microstructures. A comprehensive understanding of the dynamics of these systems will be developed, including connections to the important problem of spin transport. New measurements will provide information about low-lying excitations in the presence of a magnetic field, the dynamics of interacting magnetic vortices, and the response of domain walls to sub-nanosecond current pulses. The second area of research focuses on the origins of spin dephasing in smaller nanoparticles, in which the suppression of coherence by the generation of non-uniform spin-wave modes will be explored. The third problem addressed by this program will be the relationship between spin dynamics and spin transport in both metallic and semiconductor devices. The impact on magneto-electronics will be enhanced through collaborations with materials scientists as well as the training of graduate students in ultrafast techniques and nanofabrication.

Small magnetic particles, with dimensions much less than one micron (a human hair has a diameter of about 25 microns), are already integrated into technologies such as computer disk drives. New electronic devices have been proposed that combine small magnetic elements with semiconductor components such as transistors. This program addresses the fundamental physics that governs the behavior of small magnetic particles, sometimes called nanoparticles, on time scales of less than a nanosecond (one billionth of a second). For comparison, a 'bit' of information in a state-of-the-art computer disk can be written in about one nanosecond. The effects of shape, internal structure, and the presence of other particles will be explored using a very fast form of optical microscopy. The experiments will involve the development of new optical and microwave techniques by graduate students as well as significant collaboration with materials scientists. The development of new ultrafast magnetic devices will be investigated through interactions with other university programs as well as local industry.