Skyrmion morphology in ultrathin magnetic films

Gross, I.; Akhtar, W.; Hrabec, Aleš; Sampaio, João; Martínez, Luis; Chouaieb, S.; Shields, Brendan; Maletinsky, Patrick; Thiaville, A.; Rohart, Stanislas; Jacques, Vincent

doi:10.1103/physrevmaterials.2.024406

Cited by 72 publications

(58 citation statements)

References 47 publications

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“…Specifically, we have demonstrated that NV microscopy can simultaneously locally probe both magnetic structure and dynamics. As shown in similar thin film systems [25], pinning and disorder are important factors in determining static skyrmion bubble sizes in Ta/CoFeB/MgO. We have shown that these sizes are determined dynamically, via hopping of skymion bubble domain walls between pinning sites.…”

Section: Discussion and Future Nv Studies Of Skyrmionssupporting

confidence: 64%

“…Several imaging techniques have already been used to study skyrmions, including Kerr microscopy [10,14], Lorentz transmission electron microscopy [15,16], transmission X-ray microscopy [9], and magnetic force microscopy [12]. While each of these tools has certain advantages, a scanning probe microscope (SPM) based on the nitrogen-vacancy (NV) defect in diamond [17][18][19] is another probe particularly well-suited to studying skyrmion devices; the NV-SPM is magneti-cally non-invasive and offers quantitative, nanoscale spatial resolution of stray magnetic fields over a wide range of temperatures and magnetic fields [20][21][22][23][24][25].…”

Section: Introductionmentioning

confidence: 99%

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Single-spin sensing of domain-wall structure and dynamics in a thin-film skyrmion host

Jenkins

Pelliccione

et al. 2019

Phys. Rev. Materials

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Skyrmions are nanoscale magnetic structures with features promising for future low-power memory or logic devices. In this work, we demonstrate novel scanning techniques based on nitrogen vacancy center magnetometry that simultaneously probe both the magnetic dynamics and structure of room temperature skyrmion bubbles in a thin film system Ta/CoFeB/MgO. We confirm the handedness of the Dzyaloshinskii-Moriya interaction in this material and extract the helicity angle of the skyrmion bubbles. Our measurements also show that the skyrmion bubbles in this material change size in discrete steps, dependent on the local pinning environment, with their average size determined dynamically as their domain walls hop between pinning sites. In addition, an increase in magnetic field noise is observed near all skyrmion bubble domain walls. These measurements highlight the importance of interactions between internal degrees of freedom of skyrmion bubble domain walls and pinning sites in thin film systems. Our observations have relevance for future devices based on skyrmion bubbles where pinning interactions will determine important aspects of current-driven motion.

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Section: Discussion and Future Nv Studies Of Skyrmionssupporting

confidence: 64%

Section: Introductionmentioning

confidence: 99%

Single-spin sensing of domain-wall structure and dynamics in a thin-film skyrmion host

Jenkins

Pelliccione

et al. 2019

Phys. Rev. Materials

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“…This stochastic behavior can be attributed to the presence of pinning sites obstructing the skyrmion motion [22,23]. This local disorder can also ex-plain the large dispersion observed in the skyrmion size and shape [24][25][26] with a measured average effective diameter d Sk = 156 ± 45 nm (see Sec. 1.4 within the Supplementary Material).…”

Section: A Experimental Resultsmentioning

confidence: 97%

“…The skyrmion at rest is also distorted, since it relaxes on an inhomogeneous energy landscape, explaining the (static) deformation of some skyrmions in Fig. 1 [24][25][26]. Fig.…”

Section: Micromagnetic Simulationsmentioning

confidence: 94%

Current-Driven Skyrmion Dynamics and Drive-Dependent Skyrmion Hall Effect in an Ultrathin Film

et al. 2019

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Magnetic skyrmions are chiral spin textures that hold great promise as nanoscale information carriers. Since their first observation at room temperature, progress has been made in their currentinduced manipulation, with fast motion reported in stray-field-coupled multilayers. However, the complex spin textures with hybrid chiralities and large power dissipation in these multilayers limit their practical implementation and the fundamental understanding of their dynamics. Here, we report on the current-driven motion of Néel skyrmions with diameters in the 100-nm range in an ultrathin Pt/Co/MgO trilayer. We find that these skyrmions can be driven at a speed of 100 m s −1 and exhibit a drive-dependent skyrmion Hall effect, which is accounted for by the effect of pinning. Our experiments are well substantiated by an analytical model of the skyrmion dynamics as well as by micromagnetic simulations including material inhomogeneities. This good agreement is enabled by the simple skyrmion spin structure in our system and a thorough characterization of its static and dynamical properties.

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“…M agnetic skyrmions are nano-scale or meso-scale whirling spin configurations of topological nature which gives them some stability and long lifetime. Magnetic skyrmions have been found in a variety of non-centrosymmetric magnets 1 , in ultrathin magnetic films [2][3][4] , as well as in multiferroic insulators [5][6][7] . Quite remarkably, magnetic skyrmions can be stabilized over a wide temperature domain ranging from room temperature 8,9 to cryogenic temperature 2,3,10 .…”

mentioning

confidence: 99%

Topological superconductivity with deformable magnetic skyrmions

2019

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Magnetic skyrmions are nanoscale spin configurations that are efficiently created and manipulated. They hold great promises for next-generation spintronics applications. In parallel, the interplay of magnetism, superconductivity and spin-orbit coupling has proved to be a versatile platform for engineering topological superconductivity predicted to host non-abelian excitations, Majorana zero modes. We show that topological superconductivity can be induced by proximitizing skyrmions and conventional superconductors, without need for additional ingredients. Apart from a previously reported Majorana zero mode in the core of the skyrmion, we find a more universal chiral band of Majorana modes on the edge of the skyrmion. We show that the chiral Majorana band is effectively flat in the physically relevant parameter regime, leading to interesting robustness and scaling properties. In particular, the number of Majorana modes in the (nearly-)flat band scales with the perimeter length of the system, while being robust to local disorder. 1 arXiv:1904.03005v3 [cond-mat.supr-con] 23 Oct 2019 8 where all energies are in units of the bandwidth t, all distances are in units of the lattice spacing a (see Supplementary Note 1 and Supplementary Figure 1 for details). For precisely |m J | = |m * J | the wire is at the topological transition and has a gapless spectrum, giving our model a bulk-gap-closing point as shown in Fig. 2c.The MFB found here has a protection by a chiral symmetry, as MFB's were found to have in models with translational symmetries 39,40,51 . Note that the wire Hamiltonian and its MFB become a correct model for our texture Eq. (1) if we choose q = 0 and thereby nullify the H slope m J (r) term. Physically, this is a special case where instead of the skyrmion shape the texture becomes coplanar (in the xz-plane, see Eq. (1)), and the orthogonal direction provides a chiral operator Ξ = τ y σ ythat anticommutes with the Hamiltonian (see Eq. (2)). Since all the MFB states have the same chirality, they cannot hybridize among themselves. It is difficult to remove the MFB states 51 , namely, a perturbation must have energy larger than the effective gap; or, it should hybridize the MFB with low energy bulk states at |m J | ≈ |m * J |, which are few; or, chirality symmetry must be broken (out-of-xz-plane exchange field). We note that the proof of existence of the MFB rests on the rotational symmetry of the q = 0 coplanar texture, since this symmetry provides the m J quantum number. Consider now deformations of the shape of the edge imposed on our q = 0 coplanar texture. These geometric deformations would generally mix the m J sectors, yet the described stability of the MFB implies that the deformations would be inefficient in removing the MFB states.We can now proceed to the relevant model for a skyrmion with arbitrary q = 0:The single term H slope m J (r) breaks the chiral symmetry Ξ, and there are no other chiral operators. The term H slope m J (r) exactly contributes an energy ε edgestate (m J ) ∼ m J to an MFB state ...

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Skyrmion morphology in ultrathin magnetic films

Cited by 72 publications

References 47 publications

Single-spin sensing of domain-wall structure and dynamics in a thin-film skyrmion host

Single-spin sensing of domain-wall structure and dynamics in a thin-film skyrmion host

Current-Driven Skyrmion Dynamics and Drive-Dependent Skyrmion Hall Effect in an Ultrathin Film

Topological superconductivity with deformable magnetic skyrmions

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