AVS 50th International Symposium
    Magnetic Interfaces and Nanostructures Wednesday Sessions
       Session MI-WeM

Paper MI-WeM7
Current-Driven Magnetization Reversal at High Magnetic Fields in Co/Cu/Co Nanopillars

Wednesday, November 5, 2003, 10:20 am, Room 316

Session: Current-Induced Magnetic Switching and Excitations
Presenter: B. Oezyilmaz, New York University
Authors: B. Oezyilmaz, New York University
A.D. Kent, New York University
D. Monsma, Harvard University
J.Z. Sun, IBM T.J. Watson Research Center
M.J. Rooks, IBM T.J. Watson Research Center
R.H. Koch, IBM T.J. Watson Research Center
Correspondent: Click to Email
Recently there has been great interest in current induced angular momentum transfer in magnetic nanostructures. Its observation in point contact experiments on magnetic multilayers in the field perpendicular geometry has boosted efforts to understand the underlying mechanism.@footnote 1@ We have studied spin transfer torques in the same field perpendicular configuration in sub-micron size (~100 nm) Co/Cu/Co pillar devices at 4.2 K and 293 K. Pillars have been fabricated by means of a new nano-stencil mask process, which enables the production of large arrays of templates ideal for systematic variations of layer thicknesses and compositions. I(V) measurements in large magnetic fields (>1.5T) show an abrupt increase in device resistance at high current densities for one current polarity. The onset of this transition is marked by both a hysteretic step in the DC voltage and a hysteretic peak in dV/dI. The magnitude of the step in resistance is similar to the device in-plane GMR (~5 %) and is thus consistent with current-induced switching into a high resistance state of anti-parallel magnetization in large applied perpendicular magnetic fields. In contrast to experiments with point-contacts, our results suggest that the peak in dV/dI marks the end and not the onset of magnetization dynamics.@footnote 2@ High field hysteresis in MR measurements at fixed (positive) bias current is also observed which is consistent with this interpretation. Micromagnetic modeling that includes a spin-transfer torque is in qualitative agreement with these observations and provides an explanation for the basic features observed in the device I-V characteristics as a function of magnetic field. Further, to study the importance of the longitudinal spin-accumulation, pillars with only a single Co layer have been fabricated. Initial experiments with these Cu/Co/Cu sub-micron size pillar devices will be discussed. @FootnoteText@@footnote 1@M. Tsoi et al, Nature 406, 46 (2000). @footnote 2@B. Oezyilmaz et al., arXiv:cond-mat/0301324.