01 février 2010

Parallel (pink) and perpendicular (green) components of the spin torque exerted by a current of polarization P on the magnetization M. The green component acts like a magnetic field parallel to P, while the pink component acts like a damping or amplification on the magnetic excitations in the system. The plane defined by P and M is that of the junction’s layer surface.

Accurate experimental measurements have confirmed theoretical predictions made at Spintec concerning spin transfer torque in magnetic tunnel junctions. This effect lies at the heart of future spintronic applications.


The “spin transfer torque” concept is essential for spintronics: it opens a means for controlling magnetic devices with a current, instead of an electrical field, which is easier to implement and leads to lower electrical consumption. It is being applied in non-volatile magnetic memory applications and radiofrequency oscillators, both using a multilayer nanostructure called magnetic tunnel junction, as the basic element.


The spin polarised current which flows trough the junction will exert torque on the magnetization of a magnetic layer and change its information state. This torque has 2 components that act differently on the magnetization (see figure). Theoretical studies at Spintec and the United States have calculated these two components as a function of the voltage applied on the junction. These calculations were then experimentally validated with the help of Seoul University and Samsung. This is extremely important for the correct electrical modelling of the device and its use in computer assisted design (CAD) of electronic circuits. An example of a verified theoretical prediction is when using different magnetic electrodes for the tunnel junction creates a non-symmetrical, perpendicular spin torque component. This, in turn, seems to eliminate uncontrolled magnetization switching events which are observed for symmetrical tunnel junction elements.


Further reading: S. C. Oh et al., Nature Physics 5 (2009) 898


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