Lorentz TEM investigation of chiral spin textures and Néel Skyrmions in asymmetric 
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mrow><mml:mo>[</mml:mo><mml:mi>Pt</mml:mi><mml:mo>/</mml:mo><mml:msub><mml:mrow><mml:mo>(</mml:mo><mml:mi>Co</mml:mi><mml:mo>/</mml:mo><mml:mi>Ni</mml:mi><mml:mo>)</mml:mo></mml:mrow><mml:mi>M</mml:mi></mml:msub><mml:mo>/</mml:mo><mml:mi>Ir</mml:mi><mml:mo>]</mml:mo></mml:mrow><mml:mi>N</mml:mi></mml:msub></mml:math>
 multi-layer thin films

Li, Maxwell; Lau, Derek; Graef, Marc De; Sokalski, Vincent

doi:10.1103/physrevmaterials.3.064409

Cited by 18 publications

(14 citation statements)

References 32 publications

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“…An example of such a scenario is illustrated in Figure 3. This behavior is also in line with observed transitions from π-to 2π-VBLs in multilayer films with D < D c as the film thickness decreases [19,20]. Moreover, we anticipate that horizontal Bloch lines would exhibit similarly asymmetric behavior.…”

supporting

confidence: 88%

“…The above analysis makes a number of reasonable yet noteworthy assumptions about DW switching-in particular, that the process occurs coherently without the formation of vertical or horizontal Bloch lines (VBLs and HBLs, respectively). Li et al found that the presence of VBLs increased with decreasing thickness [19,20]. Moreover, the study in [18] concluded that HBLs mediated switching in the thick films studied; these results have recently been corroborated [21].…”

mentioning

confidence: 79%

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Deterministically switching the Bloch chirality of domain walls and skyrmions: the Dzyaloshinskii astroid

Kitcher¹,

Chen²,

Graef³

et al. 2021

Preprint

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We present a mechanism for deterministic control of the Bloch chirality in magnetic skyrmions originating from the interplay between an interfacial Dzyaloshinskii-Moriya interaction (DMI) and a perpendicular magnetic field. Although conventional interfacial DMI favors chiral Néel skyrmions, it does not break the energetic symmetry of the two Bloch chiralities in mixed Bloch-Néel skyrmions. However, the energy barrier to switching between Bloch chiralities does depend on the sense of rotation, which is dictated by the direction of the driving field. Our analysis of steady-state Dzyaloshinskii domain wall dynamics culminates in a switching diagram akin to the Stoner-Wohlfarth astroid, revealing the existence of both monochiral and multichiral Bloch regimes. Furthermore, we discuss recent theory of vertical Bloch line-mediated Bloch chirality selection in the precessional regime and extend these arguments to lower driving fields. This work establishes that applied magnetic fields can be used to dynamically switch between the chiral Bloch states of domain walls and skyrmions as indicated by this new Dzyaloshinskii astroid.

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confidence: 88%

mentioning

confidence: 79%

Deterministically switching the Bloch chirality of domain walls and skyrmions: the Dzyaloshinskii astroid

Kitcher¹,

Chen²,

Graef³

et al. 2021

Preprint

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“…Contrast can be obtained by tilting the sample, so that a fraction of the out-of-plane magnetic field is projected onto a plane perpendicular to the optical axis of the microscope (Benitez et al, 2015;Pollard et al, 2017). Fresnel defocus images have been used to study Néel-type magnetic skyrmions in a variety of multilayer samples (Pollard et al, 2017;He et al, 2018;McVitie et al, 2018;Fallon et al, 2019;Garlow et al, 2019;Jiang et al, 2019;Li et al, 2019) in the presence of different external stimuli (He et al, 2017;Zhang et al, 2018aZhang et al, , 2018b. However, it is difficult to obtain well-resolved Fresnel defocus images of small Néel-type magnetic skyrmions with high contrast for several reasons.…”

Section: Introductionmentioning

confidence: 99%

Visibility and Apparent Size of Néel-Type Magnetic Skyrmions in Fresnel Defocus Images of Multilayer Films

et al. 2021

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Multilayers that comprise thin films of heavy metals and ferromagnets have been shown to host Néel-type magnetic skyrmions at room temperature. Fresnel defocus imaging in Lorentz transmission electron microscopy is a widely used technique for recording magnetic information about skyrmions. However, the visibility of Néel-type skyrmions in Fresnel defocus images is typically low, both because only a small component of their magnetic field contributes to the signal and because of the presence of diffraction contrast from the polycrystalline multilayer structure. Here, we take advantage of the out-of-plane hysteresis in such samples to record background-subtracted Fresnel defocus images. We demonstrate an improvement in magnetic signal-to-noise ratio and spatial resolution by a factor of 3 for a (Pt/Co/NiFe)×5 multilayer. We also use simulated Fresnel defocus images of Néel-type magnetic skyrmions to understand the influence of defocus on apparent skyrmion size.

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“…The Dzyaloshinskii-Moriya interaction (DMI) found in bulk magnetic non-centrosymmetric crystals 1,2 and at the heavy metal/ferromagnetic interfaces of magnetic multi-layer films 3 has generated considerable interest in magnetic bubbles with inherent topological protection, also known as skyrmions [4][5][6][7][8] . These spin structures have been proposed for a wide range of spintronic applications, including devices for next-generation data storage 9,10 and neuromorphic computing 11,12 as they can be manipulated with remarkable efficiency using magnetic fields and electric currents 13,14 .…”

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confidence: 99%

“…Additionally, topologically trivial bubbles (Q = 0), also known as type II bubbles, have been observed in the case of weak DMI alongside achiral Bloch bubbles (see Figure 2 schematic). 8 These type II bubbles contain two vertical Bloch lines (with parallel alignment), which are 180 • transitions of the internal magnetization in a Bloch domain wall. It is noteworthy that, because a uniformly magnetized film has Q = 0, there is no required break in topology to annihilate a type 2 bubbles (i.e.…”

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confidence: 99%

Direct observation of topological charge impacting skyrmion bubble stability in Pt/Ni/Co asymmetric superlattices

Pandey

Graef

et al. 2021

APL Materials

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We characterize the magnetic properties and domain structure of Pt/Ni/Co asymmetric superlattices in comparison to the more established Pt/Co/Ni structure. This reversal in stacking sequence leads to a marked drop in interfacial magnetic anisotropy and the magnitude of the interfacial Dzyaloshinskii-Moriya interaction (DMI) as inferred from the DW structure, which we speculate could be related to a degradation of the Pt/Co interface when Pt is deposited on top of the Co layer. Lorentz transmission electron microscopy reveals exclusively Néel type domain walls and, with a perpendicular field, Néel skyrmions in the Pt/Co/Ni films. Conversely, the Pt/Ni/Co samples show only achiral Bloch domain walls, which leads to the formation of achiral Bloch (Q = 1) and type II bubbles (Q = 0) at increased perpendicular field. Combined with the reduced anisotropy leading to greater bubble densities, the latter case makes for an excellent test bed to examine the benefits of topological charge on stability. Simultaneous observation of Bloch and type II bubbles shows a roughly 50 mT larger annihilation field for the former. An in-plane component to the magnetic field is shown to both impact the structure of the formed bubbles and separately suppress the topological benefit.

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Lorentz TEM investigation of chiral spin textures and Néel Skyrmions in asymmetric [Pt/(Co/Ni)M/Ir]N multi-layer thin films

Cited by 18 publications

References 32 publications

Deterministically switching the Bloch chirality of domain walls and skyrmions: the Dzyaloshinskii astroid

Deterministically switching the Bloch chirality of domain walls and skyrmions: the Dzyaloshinskii astroid

Visibility and Apparent Size of Néel-Type Magnetic Skyrmions in Fresnel Defocus Images of Multilayer Films

Direct observation of topological charge impacting skyrmion bubble stability in Pt/Ni/Co asymmetric superlattices

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