Spin-Transfer-Torque-Assisted Domain-Wall Creep in aCo/PtMultilayer Wire

Abstract

We have studied field- and current-driven domain-wall (DW) creep motion in a perpendicularly magnetized Co/Pt multilayer wire by real-time Kerr microscopy. The application of a dc current of density of approximately < 10(7) A/cm2 assisted only the DW creeping under field in the same direction as the electron flow, a signature of spin-transfer torque effects. We develop a model dealing with both bidirectional spin-transfer effects and Joule heating, with the same dynamical exponent mu=1/4 for both field- and current-driven creep, and use it to quantify the spin-transfer efficiency as 3.6+/-0.6 Oe cm2/MA in our wires, confirming the significant nonadiabatic contribution to the spin torque.

Precise control of domain wall injection and pinning using helium and gallium focused ion beams

“…Surprisingly, a geometric approach with a large "nucleation pad" attached to one end of the device is also widely employed in PMA systems. [5][6][7] This approach works to some extent, because a larger area means a larger statistical chance of having a defect where DW nucleation is favorable. However, this approach is not very elegant, as the magnetic field needed for DW creation is not controlled and nucleation may occur at unintended spots.…”

“…1,2 In addition to the well-known DW dynamics in permalloy strips, 2,3 there is a booming interest in current-and field-induced DW motion in materials with high perpendicular magnetic anisotropy (PMA). [4][5][6][7] These materials promise efficient current-induced DW motion, because they exhibit simple and narrow Bloch walls leading to large nonadiabatic spin torque contributions. 8,9 In order to study DW physics, one needs to initially create the DWs in a reproducible way.…”

Effect of substrate temperature on the magnetic properties of epitaxial sputter-grown Co/Pt

“…The PMA leads to the formation of narrow, nanometre-scale DWs, and the large polar Kerr effect is convenient for measuring the DW motion. However, DWs tend to pin at grain boundaries in the polycrystalline Co/Pt that is typically used in these studies 9 , and this is an issue not only for investigations of the fundamental physics of DWs but also for future devices which may depend upon reliable DW motion, such as racetrack memory 14 . Epitaxial Co/Pt, in which the density of grain boundaries is minimised, could provide a solution to this problem.…”

“…Their attractive properties include perpendicular magnetic anisotropy (PMA) and a large polar magneto-optic Kerr effect (MOKE) at short wavelengths 4 . More recently Co/Pt has become an interesting system for the study of the physics of domain walls (DWs) [5][6][7][8] , and spin torque [9][10][11][12][13] . The PMA leads to the formation of narrow, nanometre-scale DWs, and the large polar Kerr effect is convenient for measuring the DW motion.…”

Spin-transfer torque efficiency measured using a Permalloy nanobridge

“…1,2 The experimentally observed consequences include domain wall ͑DW͒ motion, [3][4][5][6][7][8] depinning, [9][10][11][12] resonance, [13][14][15][16] and transformation. 17 This effect has applications in solid state storage class memories 18 and is the basis for a magnetic logic gate design.…”