AVS 49th International Symposium
    Magnetic Interfaces and Nanostructures Wednesday Sessions
       Session MI-WeA

Paper MI-WeA1
Investigation of Magnon Generation by a dc Current through a Point Contact/Magnetic Multilayer Junction

Wednesday, November 6, 2002, 2:00 pm, Room C-205

Session: Magnetization Dynamics
Presenter: W.H. Rippard, National Institute of Standards and Technology
Authors: W.H. Rippard, National Institute of Standards and Technology
M.R. Pufall, National Institute of Standards and Technology
T.J. Silva, National Institute of Standards and Technology
Correspondent: Click to Email
We have studied the spin-momentum transfer (SMT) effect with mechanical point contacts and several types of magnetic multilayers, exhibiting both ferromagnetic (FM) and antiferromagnetic (AF) exchange-coupling. Electron spins flowing though a magnetic multilayer transfer angular momentum between the individual layers. At sufficiently high current densities, the resultant spin torque is large enough to induce magnetization dynamics.@footnote 1-5@ Previous work using point contacts has shown that there is an abrupt step in the dc resistance, and corresponding peak in dV/dI, when the current reaches a critical value Ic. The linear dependence of Ic on applied magnetic field suggests a correlation with magnon generation. Earlier data were obtained from AF coupled films, with fields applied perpendicular to the film. In our measurements, we have explored a variety of parameters. We found that spin-momentum transfer is a robust effect, occurring for a wide range of experimental conditions. SMT-related phenomena are observed for both in-plane and out-of-plane fields, for AF exchange-coupled multilayers grown at both the 1st and 2nd GMR maxima, and for FM-coupled multilayers. Also, the dependence of Ic on field can vary substantially from contact to contact. Peaks in dV/dI can persist (albeit with reduced magnitude) down to zero applied field for AF-coupled samples. Multiple peaks can also occur, implying multiple excitation modes. For FM-coupled multilayers the SMT effects have large ~0.5 W steps in the dc resistance at the critical current, implying the onset of surprisingly large excitations. The persistence of SMT down to zero applied field suggests application of SMT as a novel high-frequency oscillator. @FootnoteText@@footnote 1@ M. Tsoi et al., Phys. Rev. Lett. 80, 4281 (1998) @footnote 2@L. Berger, Phys. Rev. B 54, 9353 (1996) @footnote 3@J. C. Slonczewski, J. Magn. Magn. Mater. 159, L1 (1996) @footnote 4@J. A. Katine, et al., Phys. Rev. Lett. 84, 3149 (2000) @footnote 5@E. B. Myers, et al., Science 285, 867 (1999).