Scanning electron microscopy with polarization analysis for multilayered chiral spin textures

Lucassen, Juriaan; Kloodt-Twesten, Fabian; Frömter, Robert; Oepen, Hans Peter; Duine, RA Rembert; Swagten, Hjm Henk; Koopmans, B.; Lavrijsen, Reinoud

doi:10.1063/1.4998535

Cited by 14 publications

(19 citation statements)

References 41 publications

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“…As signalled by the arrows, the magnetization inside the wall points from down to up domains, indicating a CCW Néel wall. 11,24,30 A more thorough look at the composite image of Fig. 1d suggests this is true for most domain walls at this thickness.…”

Section: IIImentioning

confidence: 80%

“…However, we estimate that the dominating contribution to the FWHM of the histogram is the result of Poisson noise in the electron counting 32 and errors in the determination of the domain-wall normal (see supplementary III). 24 We therefore give no quantitative estimation of the spread in domain-wall angles, but we know it to be much smaller than the histogram width.…”

Section: IIImentioning

confidence: 96%

“…A SEMPA measurement on a CoB thickness of t = 1.0 nm is shown in Fig. 1d 24,30,31 which is the third image in Fig. 1d and a zoom of this image is shown in Fig.…”

Section: IIImentioning

confidence: 98%

“…SEMPA combines the ability to map both in-plane (IP) magnetization components (m x and m y ) simultaneously with an extreme surface sensitivity. 21,24 We tilted the sample slightly 25 to create out-of-plane (OOP, m z ) contrast in both m y and m x such that we image both the domain walls and the OOP domains simultaneously, which allows us to extract the chirality of the top CoB layer. 24,26,27 For t ≥ 1.4 nm, the top CoB layer turns IP and starts to align along the stray fields of the underlying layer.…”

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confidence: 99%

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Tuning Magnetic Chirality by Dipolar Interactions

et al. 2019

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The role of chirality is becoming more important for new applications in spintronics, especially in ultrathin magnetic films. [1][2][3][4][5][6] In magnetic racetrack applications for example, the chirality directly determines how magnetic domain walls and skyrmions interact with the spin-orbit torques. 2,3,7-10 It is therefore important to investigate the key contributing factors to this chirality. The underlying interaction that is believed to stabilize the chirality is the Dzyaloshinskii-Moriya interaction (DMI). As shown by a wealth of theoretical and experimental reports this interaction requires the breaking of inversion symmetry and originates from the interface between a heavy metal and a ferromagnet for the thin film systems investigated in this paper. 4,11 The DMI also helps to stabilize skyrmions because it favours non-collinear spin configurations, 12 which are envisaged to be used in areas ranging from magnetic racetrack memory and logic applications, to radio frequency devices and neuromorphic computing. 5,6Very recently, however, it was realized that DMI is not the only interaction that can stabilize a specific chirality. [8][9][10][13][14][15] Actually, already 40 years ago it was shown that the presence of dipolar fields leads to the formation of chiral Néel caps. 16,17 Here, the stray fields originating from magnetic domains align the spins inside the domain walls at the top of the film to form clockwise (CW) Néel walls and and at the bottom of the film to form counterclockwise (CCW) Néel walls, providing an optimized flux closure state. Dipolar interactions can often be ignored for the thin-film systems used for domain-wall studies.Because of the increase in magnetic volume and reduced coupling across the non-magnetic spacer layers this is no longer the case for the multilayer repeat systems often used to stabilize room-temperature magnetic skyrmions. [15][16][17][18][19] Both theoretical 8-10 and experimental work 8,13,14 suggests that in these multilayer repeat systems the DMI is in direct competition with the dipolar fields. Without DMI, the dipolar interactions introduce Néel caps. Including DMI, however, leads to a larger fraction of the layers being occupied by the Néel cap of the chirality favoured by the DMI. The other cap will be reduced in size and occupy fewer layers. This happens until the DMI is so large that it is no longer energetically favourable to accommodate a Néel cap not favoured by the DMI.The energetics and dynamics of both skyrmions and domain walls are affected by this competition because it determines the net chirality of the magnetic textures, which in turn influences the interaction with, for example, spin-orbit torques. 8-10 A fundamental understanding of this competition is therefore needed to properly tailor the interactions such that

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Section: IIImentioning

confidence: 80%

Section: IIImentioning

confidence: 96%

“…A SEMPA measurement on a CoB thickness of t = 1.0 nm is shown in Fig. 1d 24,30,31 which is the third image in Fig. 1d and a zoom of this image is shown in Fig.…”

Section: IIImentioning

confidence: 98%

mentioning

confidence: 99%

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Tuning Magnetic Chirality by Dipolar Interactions

et al. 2019

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“…Even though SEMPA is in principle sensitive only to the in-plane magnetization component, we are able to detect the out-of-plane direction through a projection technique. 29 Here, we tilt the sample by an angle α with respect to the measurement axis of the detector, as is schematically depicted on the right side of Figure 1 d and e. It results in an adjustable mixing of the out-of-plane magnetization m z component in the m y channel. As we will demonstrate later on, the main component in the m y SEMPA image is given by the out-of-plane m z contrast.…”

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confidence: 99%

Chiral Spin Spirals at the Surface of the van der Waals Ferromagnet Fe₃GeTe₂

et al. 2020

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Topologically protected magnetic structures provide a robust platform for low power consumption devices for computation and data storage. Examples of these structures are skyrmions, chiral domain walls, and spin spirals. Here, we use scanning electron microscopy with polarization analysis to unveil the presence of chiral counterclockwise Néel spin spirals at the surface of a bulk van der Waals ferromagnet Fe3GeTe2 (FGT) at zero magnetic field. These Néel spin spirals survive up to FGT’s Curie temperature of T C = 220 K, with little change in the periodicity p = 300 nm of the spin spiral throughout the studied temperature range. The formation of a spin spiral showing counterclockwise rotation strongly suggests the presence of a positive Dzyaloshinskii–Moriya interaction in FGT, which provides the first steps towards the understanding of the magnetic structure of FGT. Our results additionally pave the way for chiral magnetism in van der Waals materials and their heterostructures.

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