Domain-wall velocities of up to 750 m s−1 driven by exchange-coupling torque in synthetic antiferromagnets

Abstract

The operation of racetrack memories is based on the motion of domain walls in atomically thin, perpendicularly magnetized nanowires, which are interfaced with adjacent metal layers with high spin-orbit coupling. Such domain walls have a chiral Néel structure and can be moved efficiently by electrical currents. High-capacity racetrack memory requires closely packed domain walls, but their density is limited by dipolar coupling from their fringing magnetic fields. These fields can be eliminated using a synthetic antiferromagnetic structure composed of two magnetic sub-layers, exchange-coupled via an ultrathin antiferromagnetic-coupling spacer layer. Here, we show that nanosecond-long current pulses can move domain walls in synthetic antiferromagnetic racetracks that have almost zero net magnetization. The domain walls can be moved even more efficiently and at much higher speeds (up to ∼750 m s(-1)) compared with similar racetracks in which the sub-layers are coupled ferromagnetically. This is due to a stabilization of the Néel domain wall structure, and an exchange coupling torque that is directly proportional to the strength of the antiferromagnetic exchange coupling between the two sub-layers. Moreover, the dependence of the wall velocity on the magnetic field applied along the nanowire is distinct from that of the single-layer racetrack due to the exchange coupling torque. The high domain wall velocities in racetracks that have no net magnetization allow for densely packed yet highly efficient domain-wall-based spintronics.

Compensated Ferrimagnetic Tetragonal Heusler Thin Films for Antiferromagnetic Spintronics

“…[23] The achievement of EB up to room temperature in the present bilayer films is an important step towards practical applications. Although exchange bias has been studied in some unconventional systems, such as, a ferromagnet/spin glass [24] , a ferromagnet/paramagnet [25] and a natural mineral [26] , the present exchange bias from ferrimagnet/compensated ferrimagnet is the first of its kind and has significant potential for technological applications. The flexible nature of Heusler materials to achieve tunable magnetizations, and anisotropies within closely matched materials provides a new direction to the growing field of antiferromagnetic spintronics.…”

Current-induced magnetization switching in Pt/Co/Ta with interfacial decoration by insertion of Cr to enhance perpendicular magnetic anisotropy and spin–orbit torques

“…In recent years, current induced spin-orbit torques (SOTs) in trilayer structures, where ultrathin ferromagnets (FM) is sandwiched by a heavy metal (HM) and an oxide, have attracted abundant research interests for highly effective magnetization switching [1][2][3] and fast domain wall motion [4][5][6][7][8][9][10]. In such a SOT-based device, when an in-plane charge current (J e ) flows through HM with strong spin-orbit coupling (SOC) including 5d-metal Pt [2], Ta [11], W [12], and Hf [13], etc., it can be converted into a pure spin current (J s ).…”

Spin wave eigenmodes in transversely magnetized thin film ferromagnetic wires

“…Studies of these effects such as fieldand current-induced domain wall motion [1][2][3][4][5][6][7] , domain wall magneto-resistance [8][9][10] and the interaction of spin waves with nanoscale spin textures such as domain walls, vortices and skyrmions [11][12][13][14][15][16][17] heavily rely on the understanding of transport and magnetization dynamics in ferromagnetic nanowires. More recently, ferromagnetic nanowires proved to be useful for studies of inverse spin Hall effect 19 and spin orbit torques [20][21][22][23] .…”