Ultrafast Magnetoelectronic Devices.

摘要

This research project explored new methods to coherently control magnetization dynamics in nanostructures based on a recently discovered strong and short-range quantum mechanical interaction between a spin-current and background magnetization- known as spin-transfer. This was accomplished through the fabrication and study of prototype spin-transfer devices. Specifically, we pursued the following approaches: (1) Fabrication of magnetic devices in which the magnetic anisotropy is controlled through oriented, layered or epitaxial film growth; (2) Realization of magnetic devices that combine low moment and high moment materials; and (3) High speed electrical measurements of magnetization switching and precession. We had a number of significant experimental results that have become benchmarks in the field: (1) We demonstrated spin-transfer switching with current pulses shorter than 300 psec. We also studied how the switching threshold depends on current pulse amplitude and duration for pulses between 100 ps and 1 s in duration; (2) We developed an all electrical method to study magnetization relaxation in a nanomagnet with 50 ps time relaxation and used this method to determine the relaxation time of a nanomagnet in a prototype spin-transfer device; (3) We explored highly non- linear magnetization dynamics excited by microwave spin-currents; (4) We also characterized transition metal multilayer and alloy thin films of interest in spin-transfer torque devices using broadband (1-50 GHz) ferromagnetic resonance spectroscopy.