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The recent discovery that a spin-polarized electrical current can apply a large torque to a ferromagnet, through direct transfer of spin angular momentum, offers the possibility of manipulating magnetic-device elements without applying cumbersome magnetic fields. However, a central question remains unresolved: what type of magnetic motions can be generated(More)
We present time-resolved measurements of gigahertz-scale magnetic dynamics caused by torque from a spin-polarized current. By working in the time domain, we determined the motion of the magnetic moment throughout the process of spin-transfer-driven switching, and we measured turn-on times of steady-state precessional modes. Time-resolved studies of magnetic(More)
We have fabricated nanoscale magnetic tunnel junctions ͑MTJs͒ with an additional fixed magnetic layer added above the magnetic free layer of a standard MTJ structure. This acts as a second source of spin-polarized electrons that, depending on the relative alignment of the two fixed layers, either augments or diminishes the net spin torque exerted on the(More)
The spin-transfer nano-oscillator (STNO) offers the possibility of using the transfer of spin angular momentum via spin-polarized currents to generate microwave signals. However, at present STNO microwave emission mainly relies on both large drive currents and external magnetic fields. These issues hinder the implementation of STNOs for practical(More)
We report measurements of magnetic switching and steady-state magnetic precession driven by spin-polarized currents in nanoscale magnetic tunnel junctions with low-resistance, Ͻ5 ⍀ ␮m 2 , barriers. The current densities required for magnetic switching are similar to values for all-metallic spin-valve devices. In the tunnel junctions, spin-transfer-driven(More)
We have fabricated permalloy/copper/permalloy nanopillar spin valves designed to reduce the critical current for spin-transfer switching while maintaining thermal stability of the free layer. Pulsed current amplitudes necessary for switching a 4.5-nm-thick permalloy free layer range from 0.4 mA for a 100 ns pulse to 2 mA for a 1 ns pulse, showing that the(More)
We demonstrate a technique that enables ferromagnetic resonance measurements of the normal modes for magnetic excitations in individual nanoscale ferromagnets, smaller in volume by more than a factor of 50 compared to individual ferromagnetic samples measured by other resonance techniques. Studies of the resonance frequencies, amplitudes, linewidths, and(More)
We report microwave-frequency magnetization dynamics coexcited by alternating spin torque and thermal fluctuations. In these dynamics, temperature strongly enhances the amplitude of magnetization precession and enables excitation of nonlinear dynamic states of magnetization by weak alternating spin torque. We explain these thermally-activated dynamics in(More)
We present spectral measurements of spin-wave excitations driven by direct spin-polarized current in a free layer of nanoscale Ir 20 Mn 80 /Ni 80 Fe 20 /Cu/Ni 80 Fe 20 spin valves. The measurements reveal that large-amplitude coherent spin-wave modes are excited over a wide range of bias current. The frequency of these excitations exhibits a series of jumps(More)