AVS 51st International Symposium
    Magnetic Interfaces and Nanostructures Tuesday Sessions
       Session MI-TuM

Invited Paper MI-TuM9
Spin-Transfer Torque in a Single Ferromagnetic Layer

Tuesday, November 16, 2004, 11:00 am, Room 304A

Session: Spintronics
Presenter: Y. Ji, Argonne National Lab
Authors: Y. Ji, Argonne National Lab
T.Y. Chen, Johns Hopkins University
C.L. Chien, Johns Hopkins University
M.D. Stiles, National Institute of Standards and Technology
Correspondent: Click to Email
When a spin polarized current passes through a ferromagnet, spin angular momentum can be transferred between the conduction electrons and the magnetization of the ferromagnet. As a result, a torque is imparted on the magnetization, which will be realigned toward the polarization direction of the conduction electrons, an effect called â?ospin-transfer torqueâ?. Previously most theories and experiments explore F/N/F trilayer or F/N multilayer structures, where F denotes a ferromagnet and N denotes a nonmagnetic metal. In low magnetic fields, the trilayers hysteretically switch between parallel and anti-parallel states, as the current is swept between polarities with a current perpendicular to plane (CPP) geometry. In high magnetic fields, reversible dV/dI peaks are observed for only one polarity of the current, and previously interpreted as the onset of spin-wave excitations. The multilayer or trilayer structures have been generally presumed indispensable, since non-collinear magnetizations between a polarizing layer and a receiving layer are required to generate spin torques, and the GMR effect is essential in detecting magnetization reversals. In this work, spin-transfer torque effects in a single ferromagnetic layer are demonstrated, using current injection through a point-contact. Differential resistance peaks are observed in high magnetic fields. The current values corresponding to the peak positions linearly depend on the external field. Hysteretic current-induced switching is observed in low magnetic fields. Systematic variations between low field and high field regions have been investigated and the implications will be discussed. The first author's work was done as a Ph.D. student in Johns Hopkins, supported by NSF DMR00-80031 and DMR97-32763. His current work at Argonne is supported by U.S. DOE BES-MS W-31-109-ENG-38.