The interfacial Dzyaloshinskii–Moriya interaction (DMI) emerges in ferromagnet/heavy metal thin films with broken z-mirror symmetry, stabilizing Néel domain walls and skyrmions of one chirality as dictated by its Rashba-type field. On the other hand, both Bloch chiralities remain energetically degenerate at static equilibrium for mixed domain walls in films with a moderate DMI. Multiple research groups have nevertheless independently reported significant Bloch chirality asymmetries in the Bz-stabilized domain microstructures of different interfacial DMI systems [1, 2]. In this work, we demonstrate how the asymmetric wall energy landscape in such systems can produce a deterministic Bloch chirality when domain walls are driven away from static equilibrium. For D &lt; Dc, the two ground state domain walls—having Bloch components of opposite chiralities—exhibit different restoring torques and steady state configurations. As dictated by the driving field’s direction and sign of DMI, one wall, which we term the lax wall, becomes labile at a lower Bz prior to the Walker field. At this lability point, the wall lies at an inflection point in its energy landscape and the domain wall susceptibility (χdw ∝ (σΦΦ)-1) diverges. The lax wall therefore reorients at higher fields to the steady state configuration of its counterpart, which we call the locked wall (Fig. 1). Using the Slonczewski equations and the 1D wall energy model, we analytically derived a DMI–Bz phase diagram of steady state domain wall Bloch chirality (Fig. 2), which includes an astroid analogous to the Stoner–Wohlfarth domain switching model. While these equations predict that locked walls precess beyond the Walker field, it was observed that they can instead persist due to DMI-induced asymmetries in vertical Bloch line (VBL) evolution—extending the Bloch monochirality regimes [3]. Here, we generalize these Bloch chirality preferences to arbitrary VBL behavior in these systems, before discussing how the theory of horizontal Bloch line evolution could similarly mediate Bloch chirality preferences [4].

![](https://assets.underline.io/uploads/markdown_image/1/image/c78283a8de7f53f55949028b259b7207.jpg)

Steady state Bloch monochirality via DMI-induced asymmetric evolution of lax & locked walls.

![](https://assets.underline.io/uploads/markdown_image/1/image/e73fbc654808325ad8a75b63241d4af0.jpg)

DMI–Bz phase diagram of steady state domain wall Bloch chirality

Deterministic Bloch Chirality in Interfacial DMI Systems: An Astroid for DW Switching

Discovery of the Dzyaloshinskii-Moriya Interaction (DMI) in magnetic thin films has launched an intense research effort into its effects on the structure of magnetic bubbles and domain walls including the formation of topological excitations like skyrmions. While it is well established that the internal structure of a DW transitions from a Bloch to a Néel domain wall when there is sufficient DMI, less attention has been paid to excitations contained within the domain wall. For example, recently, a new feature known as a domain wall (DW) skyrmion has been theoretically predicted and observed experimentally [1,2]. These are 360 degree rotations of the internal magnetization of a DW, which are the post-DMI analogue of a vertical Bloch line (VBL), where there is a 180 degree rotation. Moving forward, it will be important to probe excitations like these in situ to understand their dynamic behavior. Here we demonstrate the manipulation of VBLs via in-plane magnetic fields observed in situ using Lorentz transmission electron microscopy (LTEM). In this work, (Co/Ni)M multi-layers are deposited via magnetron sputtering directly onto custom-sized Si3N4 TEM membranes. We chose to examine an M=10 sample as we have previously observed an abundance of 1-π and 2-π VBLs along its DWs [3]. We note that 2-π VBLs are topologically equivalent to DW skyrmions. Fresnel mode Lorentz TEM was performed on an FEI Tecnai F20 in Lorentz mode (objective lens turned off). In-plane magnetic fields are applied in situ through the use of a Hummingbird Scientific magnetic biasing holder; the specific holder used here has a field range of ±300 Oe. In the as-prepared state, many VBLs are observed along Bloch DWs in Fresnel-mode micrographs (Fig. 1). Upon application of in-plane magnetic fields of increasing strength, we observe the movement of VBLs along DWs. When the field direction is reversed, we observe the same VBLs to move in the opposite direction. Additionally, we observe the annihilation of VBLs following the impingement of their movement by VBLs of the same winding direction. The winding of these VBLs can be reasoned to be the same sign as one another because those with opposite winding would have a zero-energy barrier to annihilation as seen in Fig. 2. Details regarding challenges to imaging, observations in high-DMI samples, and other implications of this technique will be further discussed in this presentation [4].

**References:**

 [1] R. Cheng, M. Li, A. Sapkota, A. Rai, et al., Phys. Rev. B, Vol. 99, p. 184412 (2019). [2] M. Li, A. Sapkota, A. Rai, A. Pokhrel, et al., arXiv: 2004.07888, (2020). [3] M. Li, D. Lau, M. De Graef, and V. Sokalski, Phys. Rev. Mater., Vol. 3, p. 064409, (2019). [4] This research is supported by the Defense Advanced Research Project Agency (DARPA) program on Topological Excitations in Electronics (TEE) under grant number D18AP00011. The authors also acknowledge use of the Materials Characterization Facility at Carnegie Mellon University supported by grant MCF-677785.

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/9dd928d7fad895994fe561ade50c29b7.jpg)
Micrographs of magnetic domain walls in [Co/Ni]10 samples with magnetic fields applied in the (left) ``positive" and (right) ``negative" directions. Arrows highlight positions of vertical Bloch lines whereas dotted circles indicate locations of 2-π vertical Bloch lines that have annihilated.

![](https://assets.underline.io/uploads/markdown_image/1/image/4e2179244bbc8d33a73434151e51b02a.jpg)
Micrographs of two vertical Bloch lines ``unwinding" as magnetic field strength is increased. Insets depict magnified view of circled regions with potential domain wall configuration labeled with arrows. Scale bar is 1 μm.

Direct observation of vertical Bloch line manipulation via in-plane magnetic fields

The discovery of a significant interfacial Dzyaloshinskii-Moriya Interaction (iDMI) in multi-layer thin films launched a fervent research effort into its impact on the behavior of chiral magnetic objects including domain walls (DWs).[1] The field driven creep of these Dzyaloshinskii domain walls as observed by Kerr microscopy remains a popular tool for evaluating the strength of the iDMI, but results are notoriously challenging to interpret. In this talk, we focus on experimental and theoretical investigations into the asymmetric field-driven expansion of magnetic domains in thin films with iDMI, which provide a fascinating landscape to understand creep of 1D elastic manifolds with an internal order parameter.[2] We will review early models of creep based on the DW energy, which matched well with certain experimental observations – namely, that an in-plane field (Hx) coupled with a perpendicular driving field (Hz) leads to asymmetric expansion of the domain as well as minima in the plot of x-velocity vs Hx. However, other common observations were not explained by this model including that, at large values of Hx, the high energy wall orientations reached or exceeded the velocity of low energy orientations. To explain this, Pellegren at el considered the more general elastic energy of the DW, given by the stiffness [σ(θ) + σ''(θ)].[3] By introducing a dispersive stiffness, which accounts for the finite lengthscale over which the wall deforms, it was indeed shown that the elastic energy of opposite extrema on the domain converge as Hx → ∞. This more general model explains some of the features that have also been explained by an attempt frequency that depends on wall chirality (via a chiral damping parameter).[4] The possible role of chiral damping will be discussed briefly. In more recent experiments, Brock et al showed that, in some cases – especially for weak DMI, the domain adopts a highly preferred growth direction with a dendritic structure that is neither parallel or anti-parallel to Hx.[5] The results cannot be explained by a chiral Bloch component to the DW, which would violate the symmetry of the system. Instead, we identify a steady-state DW substructure that results from the z-field torque on the internal DW magnetization (see figure 1c). This breaks the energetic mirror symmetry along the x-axis and leads to orientations of the DW with vanishing elastic energy (i.e. rapidly increased creep velocity). Remarkable agreement between an augmented form of the dispersive stiffness model (now accounting for steady-state configurations) and the experimental measurements is found. The material parameters that give rise to this seemingly anomalous behavior will be discussed. Other important factors such as internal DW excitations, field-dependent pinning, and a field-dependent DW width will be considered in this presentation as well.

**References:**

[1] Thiaville, A., Rohart, S., Jué, É., Cros, V. and Fert, A., 2012. Dynamics of Dzyaloshinskii domain walls in ultrathin magnetic films. EPL (Europhysics Letters), 100(5), p.57002. [2] Fournier, J. B. "Generalized gibbs-thomson equation and surface stiffness for materials with an orientational order parameter." Physical review letters 75.5 (1995): 854. [3] Pellegren, J.P., Lau, D. and Sokalski, V., 2017. Dispersive stiffness of Dzyaloshinskii domain walls. Physical Review Letters, 119(2), p.027203. [4] Jué, E., Safeer, C.K., Drouard, M., Lopez, A., Balint, P., Buda-Prejbeanu, L., Boulle, O., Auffret, S., Schuhl, A., Manchon, A. and Miron, I.M., 2016. Chiral damping of magnetic domain walls. Nature materials, 15(3), pp.272-277. [5] Brock, J., Medapalli, R. and Fullerton, E., 2020. Chirality-driven growth of stripe domains in Co/Ni/Pt-based multilayers. Bulletin of the American Physical Society, 65.

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/d041ea67aa2fad976e5c8d2fe441cb85.jpg)
Fig 1. Schematic of a Néel bubble subject to external magnetic field. Arrows indicate the direction of internal magnetization along the circumference. Green lines indicate time-reversal mirror planes, m'. a) No external field. Magnetic point symmetry: ∞m'm’. b) Hx only. Magnetic point symmetry: m’. c) Hx and Hz field. Magnetic point symmetry: 1.

Dzyaloshinskii Domain Wall Creep INVITED

The interfacial Dzyaloshinskii-Moriya Interaction is a critical property of magnetic thin films for the stabilization of chiral magnetic objects, including skyrmions, for use in future spintronic applications.[1] However, direct measurement of the strength of this interaction remains an experimental challenge.[2] Here, we present a technique for direct extraction of the interfacial Dzyaloshinskii-Moriya Interaction using a tapered c-shape (herein referred to as a nanohorn). A schematic of this idea is shown in figure 1. The nanohorn is designed to provide a driving force for the DW to propagate in the counter-clockwise direction driven by a reduction in the overall length of the DW itself. An in-plane magnetic field coupled with the interfacial DMI provides a driving force for propagation in the clockwise direction. This is due to the Zeeman energy associated with the DW’s internal magnetization and the magnetic field. The balance of these forces results in an energy minimum in wall position that depends directly on the strength of iDMI. In short, the rest position of the DW can be read like the needle of an analog meter to determine the strength of DMI. A series of micromagnetic calculations using Mumax3 were performed using the gradient descent approach to determine the energy of the DW as a function of its position along the nanohorn radius. Here, we use material parameters A = 15pJ/m, Keff = 598 kJ/m3, Ms = 800 kA/m for a film thickness of 2nm. The width of the magnetic nanohorn ranges from ~100-200nm although larger dimensions are not expected to significantly impact the results. The sides of this horn follow the two polar equations r = a+b-cθ, r = a-b+cθ. This produces a shape with a circular arc of radius a along its center and radial width increasing symmetrically from this arc in a linear rate 2c. We note that there are a range of parameters where there is no energy minima, which is not useful experimentally. However, the degree of horn tapering can be designed to work for material systems with different strengths of DMI. In the presentation, comparison with semi-analytical calculations will be presented, which show minimal differences in the equilibrium wall position likely due to dipolar interactions and slight tilting of the DW. Challenges associated with experimental realization of this technique will be discussed along with ways to mitigate them as evidenced by additional micromagnetic modeling. Most notably, there are dynamic limitations with driving the wall to its equilibrium, which can be addressed through increased statistics (simultaneously examining many nanohorns of different dimensions) and exciting the DW with AC magnetic fields to overcome edge pinning. Prospects for the experimental use of this technique for different materials systems will be discussed.

**References:**

[1] Thiaville, A., Rohart, S., Jué, É., Cros, V. and Fert, A., 2012. Dynamics of Dzyaloshinskii domain walls in ultrathin magnetic films. EPL (Europhysics Letters), 100(5), p.57002. [2] Lau, D., Pellegren, J.P., Nembach, H.T., Shaw, J.M. and Sokalski, V., 2018. Disentangling factors governing Dzyaloshinskii domain-wall creep in Co/Ni thin films using Pt x Ir 1− x seed layers. Physical Review B, 98(18), p.184410.

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/fb0a86c9ee7547974d3ed351125b5c6f.jpg)
Figure 1: Schematic of the coordinate system and example micromagnetic output for a nanohorn with D = 1.6 mJ/m2 and μ0Hx = 150mT. Orange arrows show the DW internal magnetization direction. Tick marks along the circumference indicate the equilibrium position (θMIN) of the domain wall for a range of other DMI strengths.

![](https://assets.underline.io/uploads/markdown_image/1/image/ac305d09aeeebe7e5935ed137942f415.jpg)
Figure 2: Domain wall energy vs wall position (θ) normalized to the energy minima for varying DMI strengths. The lines shown are empirical fits to the micromagnetic energy output. Inset: Equilibrium wall position (θMIN) vs DMI strength.

 Magnetic Nano-horns for measurement of the interfacial Dzyaloshinskii-Moriya Interaction

The Pt-Co-Ni multi-layer system has shown promising tunability of its interfacial magnetic properties (including Dzyaloshinskii-Moriya interaction (DMI) and magnetic anisotropy) for the development of future chiral spintronic devices. Previous work has shown that the system supports stabilization of Néel Skyrmions [1] and efficient movement of Dzyaloshinskii domain walls (DW) [2]. However, the vast majority of the work has focused on the case of a Pt/Co deposition order (from substrate side) leading to predominantly left-handed chiral Neel domain walls. Moreover, it is expected that there will be interesting properties that could result from combining left and right-handed domain walls in more complicated heterostructures [3]. Here, we leverage the Pt-Co/Ni multi-layer system to compare the role of the Pt/Co interface when on the bottom vs top of the asymmetric repeat unit. The film stacks under consideration are [Pt/(Co/Ni)M] N or [Pt/(Ni/Co)M]N and were deposited by DC magnetron sputtering in an argon plasma with pressure fixed at bar (2.5 mTorr). Film stacks were grown on oxidized Si substrates with a Ta/Pt seed layer to induce FCC (111) texture. Pt/(Co/Ni)M]N multi-layers show strong perpendicular magnetic anisotropy (figure 1a) with a pinched perpendicular MH loop characteristic for bubble materials. Lorentz Transmission Electron Microscopy (LTEM) shows contrast only in the tilted orientation confirming the presence of Néel-type Skyrmions and domain walls, which suggests a significant interfacial DMI strength. This is likely due to differences in the DMI associated with Pt/Co and Ni/Pt interfaces. For these samples, Brillouin Light Scattering (BLS) spectroscopy shows a shift in the spin wave spectra corresponding to |D|= 0.21 mJ/m2, which is sufficient to stabilize the Néel configuration. For the [Pt/(Ni/Co) M] N sample with all deposition conditions otherwise identical, there is a marked drop in perpendicular magnetic anisotropy with a less clearly defined pinch in the MH loop (Figure 2 a). Lorentz TEM shows only Bloch type domain walls with no preferred chirality (Figure 2 b). Furthermore, application of a perpendicular field stabilizes achiral Bloch bubbles along with a large number of topologically trivial bubbles (or type 2 bubbles) with two vertical Bloch lines inside. It is reasonable to expect that the reduction in magnetic anisotropy is related to the Pt/Co interface quality, which would in turn impact the DMI strength explaining the absence of Neel DWs. It has previously been proposed that the origin of the deposition order effect is due to intermixing between the Pt and Co [4]. It is possible the that higher adatom energy of Pt results in a higher degree of intermixing at the interface when deposited onto Co, which will be discussed along with possible steps to mitigate the problem experimentally. As a secondary note, although it has a relatively small DMI, this system can serve as a playground for evaluating the role of topology on the annihilation field of the magnetic bubbles. In-situ Lorentz TEM images show an appreciably larger annihilation field for the non-trivial bubbles (i.e. Bloch Skyrmions) than for the trivial bubbles. Statistics on the annihilation field will be presented in detail in this paper.

**References:**

1. D.Lau et al., Physical Review B, vol. 9. P. 184410 (2018) 2. S. Parkin, et al., Science, vol. 320, no. 5873, p. 190–194. (2008) 3. N. Pandey, et al., AIP Advances, vol. 10, no. 1, p. 015233. (2020) 4. R. Lavrijsen et al, Physical review B, vol 91.10, p. 104414. (2015)

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/843ae3e7665d6c08eae328e403cd669f.jpg)
Fig 1: a) M-H loop of [Pt(5Å)/Co(4Å)/Ni(6Å)]x50 multilayer structure. Fresnel mode LTEM with: b) 0° tilt and 0 T OOP field showing no DW contrast. c) 20° tilt and 0 T OOP field showing Néel wall contrast. d) 20° tilt and 0.42 T OOP field showing formation of Néel Skyrmions.

![](https://assets.underline.io/uploads/markdown_image/1/image/fb745423377868d2dcda1b3f2ed19a99.jpg)
Figure 2: a) M-H loop of [Pt(5Å)/Ni(6Å)/Co(4Å)]x50 multilayer structure. Fresnel mode LTEM with: b) 0 T OOP field showing labryinth-like DW contrast. c) 0.39 T OOP field showing growth of of bubbles from bloch domain walls. d) 0.49 T OOP field showing a mixed bubble system; red and green circles – achiral bloch bubbles, blue circle – topologically trivial bubbles (type II).

 Consequences of Pt/Co vs Co/Pt deposition order on interfacial magnetic properties in Pt-Co-Ni based asymmetric superlattices

Typically, stabilizing small, robust skyrmions requires a strong Dzyaloshinskii-Moriya Interaction (DMI). Accurately measuring the strength of DMI in prospective skyrmion host materials is therefore crucial to realizing proposed skyrmion-based devices for racetrack memory and neuromorphic computing.[1–2] In the creep regime, the velocity of a domain wall is governed by an Arrhenius law and is inversely proportional to its elastic energy.[3] Early work on the impact of DMI on domain walls showed that the resting energy of a wall is modulated by the DMI's effective field and that the presence of an in-plane field results in asymmetric domain growth due to the (mis)alignment of the two fields.[4] Subsequent studies have proposed creep models that reflect the intricacies of the relevant velocity and elastic energy scales.[5–6] As such, the sign and strength of the Rashba DMI found in thin film systems has been deduced from the asymmetric creep expansion of domains when an in-plane field is present; wall segments with core magnetizations parallel to the in-plane field have reduced energies, resulting in enhanced velocities—and vice-versa.[5–6] However, Brock et al., recently reported experimental results that deviate remarkedly from the above-mentioned creep models. Observations made in [Co(0.7 nm)/Ni(0.5 nm)/Pt(0.7 nm)]N&gt;3 films include highly asymmetric dendritic domain growth perpendicular to the in-plane field for low fields and sharp variations of the growth direction with the strength of the in-plane field.[7–8] While one study focused on the apparent preference of Bloch walls of a specific handedness and attributed most of the phenomena to interlayer DMI [8], further investigation of the findings in [7] revealed that the trends that clearly defy the symmetries expected from an intrinsically favored wall chirality with Hz.[7] In this work, we address these peculiarities by considering the impact of the driving field on the domain wall magnetization, dispersive stiffness, and creep velocity. We show that even in the creep regime, the core magnetization of a domain wall, as per the Landau-Lifshitz-Gilbert equation, can be driven to a steady-state equilibrium that deviates significantly from the static case. We find that for material parameters comparable to those reported in [7], a bubble domain in the presence of an in-plane field can exhibit sharp discontinuities in its steady-state wall magnetization profile. Similar to the findings reported in [10], such a point represents a sudden reorientation of the magnetizations along the domain wall due to the nuanced competition between the effective DMI field, the domain wall anisotropy field, the in-plane field, the driving field and Gilbert damping. Consequently, the domain wall energy and stiffness landscapes can be equally complex, highly sensitive to the in-plane field and significantly different from the static case. Incorporating a steady-state treatment of domain wall profiles into the dispersive stiffness framework developed in [5], we compute the steady-state stiffness and creep velocity profiles of a an expanding domain for the scenarios reported in [7]. As seen in Figure 2., our modelling of the N=3 film shows remarkable agreement with the observed dendritic growth directionalities as a function of the strength of the in-plane field: first propagating uniformly for very weak fields, then at 90° from the field direction, then gradually reducing to ≈20°, and then abruptly reversing direction to ≈200°. Moreover, the model reproduces the curious observation that that the propagation direction is constant for both driving field directions; switching the domain polarization switches the directions of both the DMI and applied field torques, leaving the Bloch chirality at steady state unchanged. Comparing the magnetization profiles to the propagation directions and stiffness values reveals that segments with the lowest elastic energy (and thus the highest velocity) occur close to reorientation positions in the magnetic profile. The sudden emergence of such points is also responsible for the drastic changes in the growth direction. In light of these insights, we discuss the impact of steady-state profiles on DMI values obtained via bubble expansion experiments. Finally, we consider how our steady-state stiffness model could be used in tandem with these growth experiments to more easily determine the value of Gilbert damping in thin films.

**References:**

1. R. Tomasello, E. Martinez, R. Zivieri et al., Scientific Reports., Vol. 4, (2014) 2. G. Bourianoff, D. Pinna, M. Sitte and K. Everschor-Sitte, AIP Advances., Vol. 8, p. 055602 (2018) 3. P. J. Metaxas, J. P. Jamet, A. Mougin, Physical Review Letters., Vol. 99, p. 217208 (2007) 4. S. Je, D. Kim, S. Yoo et. al., Physical Review B., Vol. 88, p. 214401 (2013) 5. J.P. Pellegren, D. Lau, and V. Sokalski. Physical Review Letters., Vol. 119, p. 027203 (2017) 6. D. Lau, J. P. Pellegren, H. T. Nembach et al., Physical Review B., Vol. 98, p. 184410 (2018) 7. J. Brock, R. Medapalli and E.E. Fullerton, Bulletin of the American Physical Society. (2020) 8. S.D. Pollard, J. A. Garlow, K. Kim,et al., Physical Review Letters., Vol. 125, p. 227203 (2020) 9. L. Sánchez-Tejerinaa, O. Alejosa, and E. Martínez, Journal of Magnetism and Magnetic Materials., Vol. 423, p. 405–410 (2017)

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/5c391c3ecd610921b55255792a947aef.jpg)
Simulated static (blue/dark) and steady-state (yellow/light) equilibrium wall magnetization profiles for an expanding bubble domain similar to those observed in [7].

![](https://assets.underline.io/uploads/markdown_image/1/image/8a760a928ff1a5a294b48a522d4d7bce.jpg)
(a) Conventions used for defining the growth direction of a domain in the presence of an in-plane field. (b) Experimental (markers) and semi-analytically computed (lines) plots of domain growth direction against in-plane field for the [Co(0.7 nm)/Ni(0.5 nm)/Pt(0.7 nm)]3 sample referenced in [7].

 Impacts of Steady-State Domain Wall Configuration on Domain Wall Stiffness and Directional Domain Propagation in the Creep Regime

The interfacial Dzyaloshinskii-Moriya Interaction has had profound consequences on the possible magnetic configurations that can be stabilized in multi-layer thin films, most notably chiral Neel skyrmions and domain walls.[1] More recently, there have been theoretical calculations and experimental work confirming the existence of an appreciable anisotropic DMI in epitaxial thin films with further reduced symmetry – namely the C2v (or mm2) point group.[2] However, so far the systems under consideration have been based on cubic crystals where the magnetocrystalline anisotropy is nearly isotropic. Here, we identify a new epitaxial relationship with C2v symmetry based on HCP Co(10.0)/FCC Pt(110). Although it is quite common to grow FCC Co(111)/Pt(111), for the case of a Pt(110) underlayer, the lattice mismatch is actually smaller for the HCP Co(10.0) orientation [as opposed to FCC Co(110)] where the c-axis lies along a single direction in the plane of the film (figure 1). Such an orientation is expected to offer some degree of anisotropic DMI based on the heavy metal Pt and reduced symmetry as well as the added feature of significant uniaxial in-plane magnetocrystalline anisotropy. Samples were prepared by DC magnetron sputtering on HF-etched Si(110) single crystal substrates. Following the work of Yang et al., we use a Ag (10nm) buffer layer, which is known to grow with (110) orientation on Si(110) at room temperature, thereby avoiding further unwanted interface diffusion.[3] This is followed by deposition of the Pt (10nm) /Co (10-50nm) bilayers, which are the focus of this work. All depositions were done in an Ar atmosphere with the working pressure fixed at 2.5 mTorr. The films were characterized structurally by standard θ/2θ x-ray diffraction (XRD) measurements and phi-scans to characterize the epitaxial relationship. The XRD scan shows primarily Ag(220), Pt(220), and Co(10.0) peaks with no identifiable Co(220) peak suggesting the film is predominantly HCP. Phi scans (figure 2) on Pt(111), Ag(111), and Co(10.1) confirm the epitaxial relationship shown in figure 1. Moreover, reciprocal space q-scans on the HCP Co spots were leveraged to characterize directional peak broadening due to stacking faults. As it is known that stacking faults cause broadening only of certain peaks (h-k ≠ 3m) along the c* direction (with breadth also determined by the parity of l), it is possible to extract the density of growth and deformation faults in the Co layer, which are found to be approximately 10% and 3% respectively in 50nm Co films. Details on how these stacking fault densities are calculated will presented in detail. Alternating gradient field magnetometry was used to measure M-H loops along different crystallographic directions in the plane of the film. A clear in-plane easy axis is identified along Si[001] (parallel to Co[0001]). The hard axis saturation field of 1.5 kOe suggests a notably smaller magnetocrystalline anisotropy than would be expected for bulk cobalt, likely due to the aforementioned stacking faults. Although the relatively thick Co layer in these films makes any interface induced DMI unlikely, the epitaxial relationship is expected to be preserved in thinner samples along with the reported uniaxial anisotropy. Together with the expected interfacial anisotropic DMI, this in-plane anisotropy makes the proposed material system an interesting playground for exploring new chiral magnetic ground states.

**References:**

[1] Thiaville, A., Rohart, S., Jué, É., Cros, V. and Fert, A., 2012. Dynamics of Dzyaloshinskii domain walls in ultrathin magnetic films. EPL (Europhysics Letters), 100(5), p.57002. [2] Hoffmann, M., Zimmermann, B., Müller, G.P., Schürhoff, D., Kiselev, N.S., Melcher, C. and Blügel, S., 2017. Antiskyrmions stabilized at interfaces by anisotropic Dzyaloshinskii-Moriya interactions. Nature communications, 8(1), pp.1-9. [3] Yang, W., Lambeth, D.N. and Laughlin, D.E., 1999. Unicrystal Co–alloy media on Si (110). Journal of applied physics, 85(8), pp.4723-4725.

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/cf10786ba9d1e164cc2eadffc57f6d46.jpg)
Fig 1. Schematic of the lattice matching for Ag(110)/Pt(110) with bottom left) FCC Co(110) or bottom right) HCP Co(10.0). The HCP (10.0) orientation has a better match along the Pt [001] direction.

![](https://assets.underline.io/uploads/markdown_image/1/image/78b7907db3cc501cd82fd177111f404e.jpg)
Fig 2. Phi scans for Pt (111), Ag (111), and Co (10.1) confirming the epitaxial relationship shown in figure 1.

 Structural and Magnetic Characterization of Epitaxial Co(10.0)/Pt(110) Multi-layers for Future Anisotropic DMI Systems Based on C2v Symmetry

**Session chair:** Sadamichi Maekawa, RIKEN


GOC - Skyrmion Dynamics

technical paper

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Vincent Sokalski

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SHORT BIO

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Deterministic Bloch Chirality in Interfacial DMI Systems: An Astroid for DW Switching

Direct observation of vertical Bloch line manipulation via in-plane magnetic fields

Dzyaloshinskii Domain Wall Creep INVITED

Magnetic Nano-horns for measurement of the interfacial Dzyaloshinskii-Moriya Interaction

Consequences of Pt/Co vs Co/Pt deposition order on interfacial magnetic properties in Pt-Co-Ni based asymmetric superlattices

Impacts of Steady-State Domain Wall Configuration on Domain Wall Stiffness and Directional Domain Propagation in the Creep Regime

Structural and Magnetic Characterization of Epitaxial Co(10.0)/Pt(110) Multi-layers for Future Anisotropic DMI Systems Based on C2v Symmetry

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