2005 APS March Meeting
Monday–Friday, March 21–25, 2005;
Los Angeles, CA
Session A43: Focus Session: Spin Transfer Effect I
8:00 AM–10:48 AM,
Monday, March 21, 2005
LACC
Room: 150C
Sponsoring
Units:
GMAG DMP
Chair: Robert Buhrman, Cornell University
Abstract ID: BAPS.2005.MAR.A43.1
Abstract: A43.00001 : Time-Domain Measurements of Nanomagnet Dynamics Driven by Spin-Polarized Current
8:00 AM–8:36 AM
Preview Abstract
Abstract
Author:
Ilya Krivorotov
(Cornell University)
The transfer of spin angular momentum from a spin-polarized current to a
nanomagnet exerts torque, and can cause the magnet's moment either to
reverse its direction or to enter a state of steady precession. Exploiting a
new nanoscale spin valve design, we make first time-resolved measurements of
these dynamics. These measurements are made in Py(4 nm)/Cu(8 nm)/Py(4
nm)/IrMn(8 nm) nanopillar spin valves in which exchange bias is used to
create a non-zero equilibrium angle between the magnetic moments of the free
and fixed permalloy (Py) nanomagnets. In the regime of steady-state
precession, the current-driven dynamics exhibit a high degree of coherence,
as evidenced by long dephasing times ($\sim $10$^{2}$ ns). Measurements of
the onset of the persistent precession in response to a current step
demonstrate a fast ($\sim $ 1 ns) response of the nanomagnet to variations
of the current.
In the switching regime, time-resolved measurements demonstrate that
spin-transfer-driven magnetization reversal in our samples is accomplished
via a process of coherent precession.
We also make time-resolved measurements of magnetic relaxation of the free
Py nanomagnet excited by a short current pulse. These measurements, made as
a function of spin-polarized current bias, demonstrate that the effective
Gilbert damping parameter can be tuned by the spin-transfer torque. The
value of the damping parameter in the limit of no current bias significantly
exceeds the damping of an extended 4 nm thick Py film -- which is
attributable to substantial spin pumping in the nanopillar structure.
Our results demonstrate that coherent nanomagnet dynamics can be generated
by spin-transfer torques in properly designed magnetic nanostructure devices
and directly measured in both the time and frequency domains. This opens a
wide range of opportunities for new types of fundamental studies of
nanomagnet dynamics and for novel technological applications in the areas of
high frequency communications and signal processing.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2005.MAR.A43.1