SPIN TRANSFER TORQUES IN MAGNETIC SEMICONDUCTOURS

Paul Haney,  Mark Stiles

When electrical current flows through a ferromagnet, it becomes spin-polarized.  This spin-polarized current (or spin current) can induce magnetic dynamics in structures with spatially varying magnetization direction.  The interaction between the spin polarized current and the magnetization is known as spin transfer torque.  Spin transfer torques are most easily understood in terms of conservation of total spin: if the spin current that flows into a volume is different than the spin current that flows out, then the spin inside the volume (i.e. the magnetization) will rotate accordingly.  Sufficiently large spin currents can induce irreversible switching of the magnetization.  In devices like magnetic random access memory in which the magnetization orientation stores data, spin transfer torque offers a fast, efficient, and scalable writing mechanism for writing information. 

In magnetic semiconductors, strong spin-orbit coupling destroys spin conservation, invalidating the simple picture of spin transfer torque described above.  Spin is coupled to orbital angular momentum, so that fluxes of spin currents can change degrees of freedom in addition to the magnetization.  For this reason spin transfer torques are not well understood in these important systems.  We study the interplay between spin currents, spin-orbit coupling, and spin transfer torque for toy models, and with first principles calculations of the magnetic semiconductor GaMnAs.  We find that the spin-orbit coupling reduces the spin transfer torque, and we offer a physical picture for spin transfer torques in these systems.

 

 


Paul Haney

Center for Nanoscale Science and Technology

A235, 216 Stop 6202

Tel: 301.975.4025

Fax:

Email: paul.haney@nist.gov

Sigma Xi member: No.

 

 

Mentors Name: Mark Stiles

Center for Nanoscale Science and Technology

A235, 216 Stop 6202

Tel: 301.975.3745

Fax:

Email: mark.stiles@nist.gov

Sigma Xi member: No.

 

Poster category:  physics.