SPIN TORQUE IN ANTIFERROMAGNETIC SYSTEMS
Paul M. Haney, mentor: M. D. Stiles. Center for Nanoscale Science and Technology, Electron Physics Group (division 620). Building 216, room 247, mail stop 6202, phone: 301-975-4025, fax: 301-926-2746, email: firstname.lastname@example.org. This work is done in collaboration with A. H. MacDonald of The University of Texas at Austin, 1 University Station C1600, Austin, TX 78712-0264. Neither I nor my mentor are members of Sigma Xi. This is a physics poster.
The interaction between electron spin and electron transport results in a class of interesting and useful phenomena, known broadly as “spintronics.” A prominent example is spin torque: an effect whereby the presence of an electric current in a magnetic system can change the orientation of the magnetization. To date, spintronics has been mostly confined to nanoscale ferromagnetic systems, such as magnetic multilayers. We propose that similar effects should be manifest in systems with other types of order, such as antiferromagnetic systems, and that these effects differ qualitatively from their ferromagnetic counterpart.
We consider specifically a thin film, multilayer geometry composed of a ferromagnetic and a compensated antiferromagnetic layer, separated by a nonmagnetic spacer. Through symmetry considerations we derive the general form of the spin torque exerted on the ferromagnet by conduction electron spins, and find that the torque tends to drive ferro- and antiferromagnetic order parameters to a perpendicular configuration. We determine the ensuing effect on the orientation of the ferromagnet through analytic and numerical solutions of the ferromagnet’s equation of motion. In a thin film geometry, we find that the application of a current should drive the ferromagnet orientation out of the easy plane. We offer experimental predictions for the observation of this effect.