Fast current-induced domain-wall motion controlled by the Rashba effect

Abstract

The propagation of magnetic domain walls induced by spin-polarized currents has launched new concepts for memory and logic devices. A wave of studies focusing on permalloy (NiFe) nanowires has found evidence for high domain-wall velocities (100 m s(-1); refs,), but has also exposed the drawbacks of this phenomenon for applications. Often the domain-wall displacements are not reproducible, their depinning from a thermally stable position is difficult and the domain-wall structural instability (Walker breakdown) limits the maximum velocity. Here, we show that the combined action of spin-transfer and spin-orbit torques offers a comprehensive solution to these problems. In an ultrathin Co nanowire, integrated in a trilayer with structural inversion asymmetry (SIA), the high spin-torque efficiency facilitates the depinning and leads to high mobility, while the SIA-mediated Rashba field controlling the domain-wall chirality stabilizes the Bloch domain-wall structure. Thus, the high-mobility regime is extended to higher current densities, allowing domain-wall velocities up to 400 m s(-1).

Direct dynamic imaging of non-adiabatic spin torque effects

“…Indeed, we also observed, for the first time, the off-resonance effects of non-adiabatic spin torques. The high value of β determined here is attractive for spintronic applications, as it implies high domain wall velocities can be obtained, which would facilitate the development of fast and lowpower technologies 8 . Moreover, the capabilities of high-resolution imaging of dynamic processes with LEM point to a new paradigm in magnetic microscopy.…”

“…Alternatively, other reports indicate that β is considerably larger than α [4][5][6] . Remedying the incomplete understanding of non-adiabatic spin torque is of particular relevance because in current driven dynamics it governs domain wall velocity, which scales linearly with β below the Walker breakdown limit, where the domain wall begins to experience turbulent motion and mobility is greatly affected [6][7][8] . Thus, the development of new spin torque devices will be facilitated by a more complete understanding of the non-adiabatic torque 9 .…”

Spatially and time-resolved magnetization dynamics driven by spin–orbit torques

“…Such a delay is a major issue for STT devices, since thermal fluctuations result in a switching time distribution that is several ns wide 22,23 . Furthermore, the SOT-induced magnetization dynamics is governed by strong damping in the monodomain regime 24,25 and fast domain wall motion in the multidomain regime [16][17][18] , both favoring rapid reversal of the magnetization.…”

“…Such a delay is a major issue for STT devices, since thermal fluctuations result in a switching time distribution that is several ns wide 22,23 . Furthermore, the SOT-induced magnetization dynamics is governed by strong damping in the monodomain regime 24,25 and fast domain wall motion in the multidomain regime [16][17][18] , both favoring rapid reversal of the magnetization.Recent investigations of SOTs in ferromagnet/heavy metal layers showed that reliable switching can be achieved by the injection of current pulses as short as 200 ps in Pt/Co and Ta/CoFeB structures 1,26,27 . However, these experiments only measured the switching probability as a function of pulse amplitude and duration, while the mechanism and the timescale of magnetization reversal remain unknown.…”

Experimental Demonstration of Complete 180° Reversal of Magnetization in Isolated Co Nanomagnets on a PMN–PT Substrate with Voltage Generated Strain

“…Popular approaches include passing a spin current through the soft layer to generate a spin transfer torque [2][3][4][5][6][7] or spin orbit torque [8][9][10][11] or domain wall motion [12][13] . Other approaches involve using voltage controlled magnetic anisotropy 14 , magnetoelectric effects [15][16][17] , magnetoionic effects 18 and magnetoelastic effects [19][20][21][22][23][24][25] .…”