Dynamics of Nanomagnets Driven by Spin-Polarized Current Ilya Krivorotov Cornell University Spin-polarized electrons traversing a ferromagnet can transfer spin angular momentum to the local magnetization, thereby inducing magnetization reversal or exciting persistent magnetization dynamics. To understand the mechanism of this recently discovered effect, we make time-resolved measurements of spin-transfer-driven excitations in nanoscale ferromagnetic dots. We find that spin-polarized current drives coherent magnetic excitations with coherence significantly exceeding that of the field-driven modes observed in ferromagnetic resonance experiments. In the switching regime, spin-transfer-driven magnetization reversal is accomplished via a process of precession, and the switching time is determined by a competition between transfer of angular momentum and magnetic energy dissipation. We also observed that magnetic relaxation in the presence of spin-polarized current is strongly current-dependent. Our observations provide experimental support to spin torque model of spin transfer effect and demonstrate feasibility of technological applications of spin transfer in the areas of high frequency communications and non-volatile electronics.