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In the era of social media, storage of information plays an important role. Magnetic domain wall memory devices are promising alternatives to hard disk drives for high-capacity storage. One of the challenges in making these devices for practical application is a precise control of domain wall displacement in nanowires. Researchers have extensively studied domain wall pinning based on topographical notches fabricated by lithography. However, scaling the domain wall memory to nanoscale requires better domain wall pinning strategies. In this letter, we demonstrate that the localized modification of magnetic properties in Co/Pd multilayer-based nanowires by ion implantation is an effective non-topographical approach to pin domain walls. First, by micromagnetic simulations, it is shown that the areas, where the composition is modified to tune the anisotropy and magnetization, act as domain wall pinning centers. Experimentally, from magnetization measurements and X-ray diffraction measurements at the thin film level, it is shown that the ion-implantation is effective in changing magnetic anisotropy. Devices have also been fabricated and, using Kerr images at different applied fields, it is shown that the domain walls are pinned at the B þ ion-implanted regions. These results demonstrate that localized compositional modification using ion-implantation can pin domain walls precisely. The achieved results are useful toward realizing high-capacity information storage.Domain wall (DW)-based devices such as racetrack memory have been proposed as promising candidates for high capacity, non-volatile information storage to replace hard disk drives. [1,2] In DW memory (DWM) with a perpendicular magnetic anisotropy (PMA), the domains with magnetization pointing up represent "1" and the regions with magnetization pointing down represent "0." [2,3] In order to read and write information, the DWs are moved by an electrical current which causes motion by the spin-transfer torque (STT) mechanism. [4][5][6][7] Spin Hall effect in heavy metal/ferromagnetic/insulator structures is another mechanism in which a torque is exerted by pure spin current. [8,9] In comparison to STT driving DW motion, pure spin-polarized current gives a high speed performance of DW devices. [10,11] The speed of DW motion in certain designs could reach km s À1 . [11] In order to increase the capacity of DWM, researchers proposed fabricating U-shape vertical nanowire to store data, like the trees planted in the forest. However, fabrication of such devices is challenging particularly for commercial purposes. The other structure is horizontal stripe shape, which suffers from the data storing overflowing issues because the two ends of nanowire cannot be connected. Zhang et al. [12] proposed a ring structure with DW ratchets, which could be utilized for addressing the data overflow issue without any additional overhead.For DW-based devices, the propagation of DWs show a stochastic behavior. This stochastic manner was a significant challenge for magnetic recording comm...

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Spin-orbit torque (SOT) induced by electric current has attracted extensive attention as an efficient method of controlling the magnetization in nanomagnetic structures. SOT-induced magnetization reversal is usually achieved with the aid of an in-plane bias magnetic field. In this paper, we show that by selecting a film stack with weak out-of-plane magnetic anisotropy, field-free SOT-induced switching can be achieved in micron sized multilayers. Using direct current, deterministic bipolar magnetization reversal is obtained in Pt/[Co/Ni]2/Co/Ta structures. Kerr imaging reveals that the SOT-induced magnetization switching process is completed via the nucleation of reverse domain and propagation of domain wall in the system.

In this work, we show that domain wall (DW) dynamics within a system provide an alternative platform to characterizing spin-orbit torque (SOT) effective fields. In perpendicularly magnetized wires with a Pt/(Co/Ni) 4 /Co/IrMn stack structure, differential Kerr imaging shows that the magnetization switching process is via the nucleation of the embryo state followed by domain wall propagation. By probing the current induced DW motion in the presence of in-plane field, the SOT effective fields are obtained using the harmonic Hall voltage scheme. The effective anisotropy field of the structure decreases by 12% due to the SOT effective fields, as the in-plane current in the wire is increased.

The spin-orbit torque (SOT) effective fields, namely field-like and damping-like terms, depend on the thicknesses of heavy metal (HM) and ferromagnetic metal (FM) layers, in a stack comprising of HM/FM/HM or oxide. In this work, we report on the dependence of the SOT effective fields on the magnetization uniformity in the wires comprising of Ta/Co/Pt layer structure. SOT dependence on magnetization uniformity dependence was investigated by concurrent variation of the magnetization uniformity in Co layer and characterization of the SOT effective fields in each wire which excludes the layer thickness dependence influences. Our experimental results reveal that the field-like term decreases while the damping-like term increases with increasing Co magnetization uniformity. The magnetization uniformity influence on the effective fields is attributed to the spin Hall effect, which contributes to the SOT.

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Simultaneous determination of effective spin-orbit torque elds in magnetic structures with in-plane anisotropy. Physical Review B, 95, article no. 174415. For guidance on citations see FAQs.