High-speed dynamics, damping, and relaxation times in submicrometer spin-valve devices

The dynamical response of spin-valve devices with linewidths of 0.8 mu m has been measured after excitation with 160 ps magnetic impulses. The devices show resonant frequencies of 2-4 GHz which determine the upper limit of their operation frequency. The dynamical response can be fit with Landau-Lifshitz models to extract an effective uniform-mode damping constant, alpha(um). The measured values of alpha(um) were between 0.04 and 0.01 depending on the magnitude of the longitudinal bias field. The appropriate damping coefficient for use in micromagnetic modeling, alpha(mm), was extracted from the dynamical response with large longitudinal bias field. This value was used to model the switching of a 0.1 mu mx1.0 mu m magnetoresistive random access memory cell. The micromagnetic model included shape disorder that is expected to be found in real devices. The simulations showed that, while the magnetization reverses rapidly (< 0.5 ns), it took several nanoseconds for the energy to be removed from the magnetic system. The switching energy was stored in short wavelength magnetic fluctuations that could dramatically affect the re-reversal process 1-2 ns after the first reversal. [S0021-8979(00)70908-X].