We describe variations in the resistance of $\mathrm{Co}/\mathrm{Cu}$ multilayers, induced by means of a high current density $\approx {10}^8\mathrm{A}/{\mathrm{cm}}^2$ injected into the multilayer through a point contact. We propose that the observed resistance changes are due to excitations of zero-wave-number spin waves in the magnetic layers. As predicted, such current-driven excitation of a magnetic multilayer occurs for only one direction of current flow and has a current threshold which increases linearly with the applied magnetic field.

• Received 21 November 1997

DOI:https://doi.org/10.1103/PhysRevLett.80.4281