Magnetization dynamics and spin torque effect in nanoscale magnetic bi-and trilayer systems

Event Sponsor: 
Energy Sciences and Engineering
Start Date: 
Apr 16 2010 - 11:00am to 12:00pm
Building/Room: 
Building 223 Room S-105
Location: 
Argonne National Laboratory
Speaker(s): 
Olle G. Heinonen
Speaker(s) Title: 
Seagate Technology
Host: 
J. Hryn, W. Kwok, D. Mancini, S. Streiffer

Magnetization dynamics in nanoscale patterned multilayer systems has been the subject of very active research over the past decade. This is because new and interesting phenomena occur and are observable in nanoscale magnetic systems, as a result of size confinement and proximity effects. Some of the key areas addressed by recent research are vortex dynamics and the nature and dispersion of spin wave eigenmodes, and what controls them, as well as the effect of spin torque.

I will here present results on micromagnetic modeling of vortex dynamics and low-lying spin wave eigenmodes in circularly exchange biased bi- and trilayer discs. In these systems, the equilibrium magnetization is in a vortex configuration, and one layer is in contact with an antiferromagnet with the exchange bias set with the ferromagnet in a vortex configuration. The dynamics can be controlled by the exchange bias strength and by the interlayer exchange coupling.

I will also discuss spin torque effects, in which a spin-polarized current exerts a torque on the magnetic layers. It is known that the spin torque contains two components, one in-plane and one perpendicular component. Both are important in magnetic tunnel junctions, but the perpendicular component has been notoriously difficult to measure. The modeling that I have carried out shows that the strength of the so-called perpendicular spin torque affects the lowest spin wave eigenmode, and thus enables simple experimental determination of the value of the perpendicular spin torque.

I will show some very recent experimental results on magnetic tunnel junctions about 50 nm in lateral size in which the lowest ferromagnetic resonance frequency is shifted by bias voltage and how this shift is directly proportional to the perpendicular spin torque component.

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