Current-induced magnetic excitations in Co/Cu/Co bilayer nanopillars
(∼50 nm in diameter) have been studied experimentally at low temperatures
for large applied fields perpendicular to the layers. At sufficiently high
current densities excitations, which lead to a decrease in differential
resistance, are observed for both current polarities. Such bipolar excitations
are not expected in a single domain model of spin-transfer. We propose that at
high current densities strong asymmetries in the longitudinal spin accumulation
cause spin-wave instabilities transverse to the current direction in bilayer
samples, similar to those we have reported for single magnetic layer junctions.Comment: 4 pages, 4 figures+ 2 additional jpg figures (Fig. 2d and Fig. 3)
high resolution figures and recent related articles are available at:
http://www.physics.nyu.edu/kentlab/news.htm
