Current-induced domain wall motion in Co/Pt nanowires: Separating spin torque and Oersted-field effects

Abstract

We report on low temperature current induced domain wall depinning experiments on (Co/Pt) multilayer nanowires with perpendicular magnetization. Using a special experimental scheme, we are able to extract the different contributions of the Oersted field and spin torque from the dependence of the depinning field on the injected current for selected magnetization configurations. The spin torque contribution is found to be dominant with a small contribution of the Oersted field leading to a nonadiabaticity factor β in line with previous measurements.

Extraction of the spin torque non-adiabaticity from thermally activated domain wall hopping

“…Slowly increasing the field in the opposite direction leads to a change in the time resolved extraordinary Hall voltage. As in previous experiments, 14,18 we are able to pin the DW within the Hall cross by relaxing the field back to zero before a complete reversal of the magnetization within the Hall cross occurs. We then find that at zero field the extraordinary Hall voltage changes stochastically due to thermally activated DW hopping between pinning sites.…”

“…These values are consistent with what was measured using the current-field equivalency at larger current densities. 14,18 Now we compare these results to measurements of the dwell times for the hopping at constant fields as a function of current (see Fig. 2(b)) that allow us to independently determine the non-adiabaticity factor b.…”

“…Furthermore, the problem of possible Oersted field contributions exists in this approach, but employing depinning field measurements at a constant cryostat temperature using two different initial magnetization configurations allows for the distinction between the spin torque and the Oersted field contribution confirming values of b > a. 18 So there is a clear discrepancy between the values extracted from the different approaches (b % a or b > a), and it is unclear whether this is due to the different samples used or due to the different methods that do not extract exactly the same information. To determine whether it is the sample or the method that leads to the different values of b, one needs to ideally use the different methods on the same sample.…”

Manipulation of multiple 360o domain wall structures and its current-driven motion in a magnetic nanostripe

“…2 In recent years, the motion of single domain wall (DW) due to a spin transfer torque of electrons has been well studied theoretically [3][4][5][6] and experimentally. [7][8][9][10][11] For instance, it was known that the velocity of DW increases linearly with the increasing of the applied current, and when the applied current is higher than a critical value, a dramatic reduction in DW average velocity occurs due to Walker breakdown. [12][13][14] However, for the application of data storage, there must be multiple DWs in a magnetic nanostripe.…”

Domain-wall pinning by local control of anisotropy in Pt/Co/Pt strips

“…Regarding the topic of current-induced DW dynamics, most is known about DWs in in-plane magnetized permalloy strips [16]. Recently, the focus has been shifting toward materials with high perpendicular magnetic anisotropy (PMA) [17,18,19,20,21,22,23,24,25]. Although field-driven DW motion is typically slow due to DW creep [26,27,28], these materials might show faster currentinduced DW motion, because they exhibit simple and narrow DWs potentially leading to large non-adiabatic spin torque contributions [29,30,31], or by the presence of Rashba fields stabilizing the DW structure during propagation [22].…”