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

Franken, JH Jeroen; Hoeijmakers, M Mark; Lavrijsen, Reinoud; Kohlhepp, JT Jürgen; Swagten, Hjm Henk; Koopmans, B.; Veldhoven, van E Edwin; Maas, DJ

doi:10.1063/1.3549589

Cited by 60 publications

(58 citation statements)

References 20 publications

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“…Reproducible operation of such a device requires well-defined pinning sites, which are typically realized by locally altering the geometry 28 or material properties. [29][30][31] The ability to activate and deactivate these pinning sites, preferably at fast timescales, provides new device options and could greatly reduce the current density needed to move the domain walls from site to site. The devices by Bauer et al 26 relied on the effect of electromigration, which has its own advantages and disadvantages.…”

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confidence: 99%

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Voltage-gated pinning in a magnetic domain-wall conduit

Franken

Yin

Schellekens

et al. 2013

Applied Physics Letters

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In spintronic devices relying on magnetic domain-wall (DW) motion, robust control over the DW position is required. We use electric-field control of perpendicular magnetic anisotropy to create a voltage-gated pinning site in a microstructured Pt/Co/AlOx DW conduit. A DW pins at the edge of a gate electrode, and the strength of pinning can be tuned linearly and reversibly with an efficiency of 0.22(1) mT/V. This result is supported by a micromagnetic model, taking full account of the anisotropy step at the gate edge, which is directly caused by a change in the electron density due to the choice of material.

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confidence: 99%

“…We now turn to a simple DW-energy model in order to verify these results, in particular, the magnitude of the observed pinning effect. In the previous experiments on permanent DW pinning sites created by Focused Ion Beam irradiation, 29,30 we developed a model to describe the pinning field at an anisotropy step DK (Ref. 30)…”

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confidence: 99%

Voltage-gated pinning in a magnetic domain-wall conduit

Franken

Yin

Schellekens

et al. 2013

Applied Physics Letters

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“…3(a). Here, the red part indicates the region irradiated by Ga ions which reduce the perpendicular magnetic anisotropy and allow the nucleation of DWs on two sides [21]. However, this straight wire is not suitable for measuring the chiral resistance, as we will experimentally show later on, because the DW pair has an opposite chirality when applying a high in-plane field.…”

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confidence: 99%

Chiral magnetoresistance in Pt/Co/Pt zigzag wires

Yin

Han

Kim

et al. 2017

Applied Physics Letters

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The Rashba effect leads to a chiral precession of the spins of moving electrons while the Dzyaloshinskii-Moriya interaction (DMI) generates preference towards a chiral profile of local spins. We predict that the exchange interaction between these two spin systems results in a 'chiral' magnetoresistance depending on the chirality of the local spin texture. We observe this magnetoresistance by measuring the domain wall (DW) resistance in a uniquely designed Pt/Co/Pt zigzag wire, and by changing the chirality of the DW with applying an in-plane magnetic field. A chirality-dependent DW resistance is found, and a quantitative analysis shows a good agreement with a theory based on the Rashba model. Moreover, the DW resistance measurement allows us to independently determine the strength of the Rashba effect and the DMI simultaneously, and the result implies a possible correlation between the Rashba effect, the DMI, and the symmetric Heisenberg exchange.In a magnetic system with inversion symmetry breaking combined with spin-orbit coupling (SOC), a variety of chirality-related phenomena occur. For instance, due to the Rashba effect [1], the spins of the conduction electrons flowing at an interface are subject to an effective in-plane magnetic field due to the relativistic SOC, resulting in spin precession around the field during its transport. In this case, the direction of the magnetic field depends on the electron flow direction. In contrast, the precession of the conduction spins, as can be seen from comparing Figs. 1(a) and 1(b), is independent of the flow direction and shares the same rotational sense (denoted by a chirality of electrons, C e ) [2]. Apart from the chiral behavior of the conduction spins, the chiral nature of localized spins has recently been discovered in ferromagnetic materials with inversion asymmetry and SOC. This gives rise to the Dzyaloshinskii-Moriya interaction (DMI) [3,4] leading to a chiral spin texture of the localized spins (C m ), manifested as Néel type magnetic domain walls (DWs) [5] and magnetic skyrmions [6], which are crucial to the future design of spintronic devices.Although these two effects originate in different spin systems, one can speculate about their interplay through exchange interaction between the conduction and localized spins [7][8][9]. This results in a magnetoresistance (MR) which arises when the conduction electron spins propagate with a fixed chirality due to Rashba-type SOC and interact with the chiral DMI-induced magnetic texture. As shown in Figs. 1(c) and 1(d), this should lead to lower (higher) resistance when C e is identical (opposite) to C m . This MR can be termed as 'chiral MR', since the magnitude of the MR varies for spin The chirality of the profile of the spin precession is identical (Ce = +1) for both signs of k. (c)(d) Inside a chiral magnetic texture with chirality Cm (green arrows), the rotation of electron spins generally follow the local spins due to exchange interaction while finite degree of misalignment is inevitable, which gives rise to t...

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“…One way to change the injection properties and to circumvent the issue described above is to change the boundary between the irradiated and unirradiated regions. 12,16 In the experimental data described above the region between the two parts of the nanowire was defined by the Gaussian width of the FIB beam. This is around 3.5 nm at the focal point of the beam.…”

Section: Domain Wall Nucleation and Injectionmentioning

confidence: 99%

“…Various methods to achieve this have been demonstrated including local Oersted fields, 6 manipulation of the in-plane shape 10,11 and irradiation by focussed ion beam (FIB). 12,13 FIB irradiation of perpendicular materials has been shown to reduce the anisotropy of the irradiated area, largely by causing intermixing of the heavy metal/magnetic interfaces which provide the perpendicular anisotropy. 14 The perpendicular anisotropy is a competition between an interfacial magnetocrystalline anisotropy and the demagnetizing energy of the layer.…”

Section: Introductionmentioning

confidence: 99%

Controlling domain wall nucleation and injection through focussed ion beam irradiation in perpendicularly magnetized nanowires

et al. 2017

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Using Ga+ focussed ion beam irradiation of Ta/Pt/CoFeB/Pt perpendicularly magnetized nanowires, the nucleation and injection fields of domain walls into the nanowires is controlled. The nucleation and injection fields can be varied as a function of dose, however, the range of injection fields is found to be limited by the creation of a step in anisotropy between the irradiated and unirradiated regions. This can be altered by defocussing the beam, which allows the injection fields to be further reduced. The ability to define an arbitrary dose profile allows domain walls to be injected at different fields either side of an asymmetrically irradiated area, which could form the initial stage of a logic device. The effect of the thickness of the magnetic layer and the thickness of a Ta underlayer on the dose required to remove the perpendicular anisotropy is also studied and is seen that for similar Ta underlayers the dose is determined by the thickness of the magnetic layer rather than its anisotropy. This finding is supported by some transport of ions in matter simulations.

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

Cited by 60 publications

References 20 publications

Voltage-gated pinning in a magnetic domain-wall conduit

Voltage-gated pinning in a magnetic domain-wall conduit

Chiral magnetoresistance in Pt/Co/Pt zigzag wires

Controlling domain wall nucleation and injection through focussed ion beam irradiation in perpendicularly magnetized nanowires

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