Dr. Olle Heinonen
Argonne National Laboratory
Materials Science Division
|TITLE:||"Spin torque and magnetization dynamics in magnetic tunnel junctions"|
|DATE:||Thursday, April 28, 2011|
|PLACE:||Building 212 / A-157|
Refreshments will be served at 10:45 a.m.
ABSTRACT: Some 25 years ago, Slonzcewski and Berger independently realized that a dc charge current applied to a structure with non-collinear magnetization may exert a torque on the magnetization. This effect is particularly pronounced in nanoscale heterostructures such as spin valves, which have the basic structure ferromagnet/normal metal/ferromagnet, or magnetic tunnel junctions (MTJs) which have the structure ferromagnet/insulator/ferromagnet. MTJs in which the barrier is MgO are particularly interesting since the tunneling magnetoresistance - the change in resistance as the magnetization in the ferromagnetic layers change relative orientation - and spin torque effects can be very large. In these structures, a dc current can lead to spin-torque induced oscillations, noise, instabilities, and switching of the magnetization orientations. I will in this presentation first give a background of the origin of the spin torque and discuss its two components, the so-called in-plane component and the perpendicular component. The former is rather well understood while the latter is more complex. I will present some experimental results and modeling results aimed at understanding the magnitude of the perpendicular spin torque component and its consequences for the magnetization behavior in MTJs. In the latter part of the presentation, I will discuss some recent experimental results and their modeling interpretations of some interesting and complex behavior of the resonances of the magnetization dynamics in nanoscale MTJs.