Direct-Current Induced Dynamics in Co90Fe10/Ni80Fe20 Point Contacts
William H. Rippard, Matthew R. Pufall, Shehzaad F. Kaka, Stephen E. Russek, Thomas J. Silva
We have directly measured coherent high-frequency magnetization dynamics in ferromagnetic films induced by a spin-polarized dc current. The precision frequency can be tuned over a range of several gigahertz by varying the applied current. The frequencies of excitation also vary with applied field, resulting in a microwave oscillator that can be tuned from below 5 to above 40 GHz. This novel method of inducing high-frequency dynamics yields oscillation having quality factors from 200 to 800. We compare our results with those from single-domain simulation of current induced dynamics.