|RF Assisted Spin Transfer Switching in GMR Nanostructures |
Electrical and Computer Engineering
|Sylvia Florez, Hitachi Global Storage Technologies, San Jose, CA|
11:00 AM, EE-240 (Electrical Engineering)
As the electronics industry strives for miniaturization of devices and components, electron quantum effects become a limiting factor. However, by exploiting the 'spin' of the electron rather than its charge, it may be possible to create a new generation of smaller and more versatile 'spintronic' devices. Nanomagnetics, a key area to this exploration, and the broad subject of Dr.. Florez's work, is now at the forefront of scientific interest. Remarkable discoveries in this field, such as the spin-transfer effect [1-4], are unquestionably of high potential technological impact.
This talk covers Dr. Florez's current work on spin transfer, as well as an outlook on future key challenges in this field. Spin transfer gives rise to a new set of current-induced dynamic excitations and magnetic switching phenomena with applications in rf engineering and high-density, non-volatile memory devices, such as MRAM. For the latter, reducing the dc critical currents required for switching is a critical objective and an important focus of my work. To this end, Dr. Florez has studied spin-transfer induced switching in current-perpendicular-to-plane (CPP) giant magnetoresistive (GMR) nanoscale pillars when driven by combined dc plus rf currents. The experiments reveal that, at low temperature, the rf currents can dramatically alter the dc current driven free layer magnetization reversal dynamics, as well as the switching level of these devices. These effects are observed when the frequency of the rf current, fext, is tuned to be within a narrow range around the dc driven magnetization precession frequencies, f0dc. For these frequencies, interactions between the dc driven dynamic excitations and the injected rf induce frequency locking and frequency pulling effects that lead to a measurable dependence of the critical switching current on the frequency of the injected rf current. I will also present macrospin simulation results, based on the Landau-Lifshitz-Gilbert equation using the Slonczewski spin-transfer torque (STT) , that qualitatively capture the underlying physics.
 L. Berger, Phys. Rev. B 54, 9353 (1996).
 J. Slonczewski, J. Magn. Magn. Mater. 195, L261 (1996).
 J. A. Katine et al.,Phys. Rev. Lett. 84, 3149 (2000).
 S. I. Kiselev et al., Nature 425, 380 (2003).