Professor Ilya Krivorotov
Physics Department
University of California, Irvine


"Magnetization Dynamics Excited by Spin-Polarized Current"

Spin-polarized electrons traversing a ferromagnet can transfer spin angular momentum to the local magnetization, thereby inducing magnetization reversal or exciting persistent spin waves. To understand the mechanism of this effect, we make time and frequency-resolved measurements of spin-transfer-driven excitations in nanoscale ferromagnetic dots. We find that spin-polarized current can generate coherent persistent oscillations of magnetization of the nanomagnet in extremely non-linear regimes. Comparison of the spectral properties of these excitations to those predicted by micromagnetic simulations provides tests of theories of non-linear magnetizations dynamics. In the switching regime, magnetization reversal induced by spin-polarized current proceeds via a process of precession, and the switching time is determined by competition between transfer of angular momentum and magnetic energy dissipation. Measurements of magnetic relaxation in the presence of spin-polarized current show that the relaxation process is strongly current-dependent. Our observations provide tests of spin transfer theories and demonstrate feasibility of technological applications of spin transfer in high frequency communications and non-volatile electronics.