IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Magnetic Interfaces and Nanostructures Monday Sessions
       Session MI+NS-MoA

Invited Paper MI+NS-MoA3
Torques and Tunneling in Nanomagnets

Monday, October 29, 2001, 2:40 pm, Room 110

Session: Nano Magnetics
Presenter: D.C. Ralph, Cornell University
Authors: D.C. Ralph, Cornell University
E.B. Myers, Cornell University
M.M. Deshmukh, Cornell University
E. Bonet, Cornell University
F.J. Albert, Cornell University
R.A. Buhrman, Cornell University
Correspondent: Click to Email
When the size scale of magnetic devices is shrunk to nanometer dimensions, qualitatively new properties can emerge. I will discuss two recent examples. First, I will review investigations of a new mechanism -- spin-transfer -- by which applied currents can be used to manipulate the orientation of ferromagnetic moments. Unlike traditional schemes which utilize a magnetic field to control magnetic reorientation, spin-transfer is based on the exchange interaction. It is a torque that results when a spin-polarized current scatters from a magnetic element, and in the process transfers spin-angular momentum to the magnet. Depending on device geometry and the magnitude of the applied magnetic field, this torque can cause either controlled magnetic reversal or the excitation of high-frequency precession driven by a dc current. Another property that emerges only in devices containing metal grains smaller than about 10 nm in diameter is that the electronic states involved in electron transport can be resolved individually. I will discuss spectroscopic measurements of the electronic states which contribute to electron tunneling in cobalt nanomagnets containing about 1000 atoms, and how these states are influenced by exchange interactions, anisotropy forces, and applied magnetic fields. We find that each electronic state in given magnetic nanoparticle is described by a slightly different anisotropy energy, with fluctuations of order 1 to 3 percent. Individual states are not purely spin-up or spin-down, but have a mixed character. Spin-waves and non-equilibrium excitations play a central role in shaping the tunneling spectrum, even at low energies.