Significant Enhancement of Spin-Transfer Torque in Ultra-narrow Domain Wall
Sug-Bong Choe (1Center for Subwavelength Optics and Department of Physics, Seoul National University, Seoul 151-742, Republic of Korea)

In the last decade, there have been remarkable advances in the study of current-induced domain wall (DW) motion as the key operation principle of emerging memory and logic devices. As the major driving mechanism of the DW motion, spin-orbit torque (SOT) with chiral DWs draws great attention nowadays, which explains the direction of DW motions in heavy metal/transition metal/oxide films. However, here we demonstrate that the spin-transfer torque (STT) is significantly enhanced in ultra-thin Co films sandwiched by Pt layers and consequently, plays a major role in determining the direction of DW motions. Such significant enhancement is attributed to the ultra-narrow DW width down to about 1 nm, which considerably boosts up the nonadiabaticity of the conduction electrons. Moreover, the sign of the enhanced STT is found to be negative, possibly caused by either a negative nonadiabaticity or a negative spin polarization, which results in the DW motion along the current direction. The detailed experimental procedures and results will be discussed.