Imaging the magnetic nanowire cross-section and magnetic ordering within a suspended 3D artificial spin-ice

Artificial spin-ice systems are patterned arrays of magnetic nanoislands, arranged into frustrated geometries and provide insight into the physics of ordering and emergence. The majority of these systems have been realised in two-dimensions, mainly due to ease of fabrication but with recent developments in advanced nanolithography, three-dimensional artificial spin ice (ASI) structures have become possible providing a new paradigm in their study. Such artificially engineered 3D systems provide new opportunities in realising tuneable ground states, new domain wall topologies, monopole propagation and advanced device concepts such as magnetic racetrack memory. Direct imaging of 3DASI’s with magnetic force microscopy (MFM) has thus far been key to probing the physics of these systems but is limited in both depth of measurement and resolution, ultimately restricting measurement to the uppermost layers of the system. In this work, a method is developed to fabricate 3DASI lattices over an aperture using two-photon lithography, thermal evaporation, and oxygen plasma exposure allowing the probe of element-specific structural and magnetic information using soft x-ray microscopy with x-ray magnetic circular dichroism (XMCD) as magnetic contrast. The suspended polymer-permalloy lattices are found to be stable under repeated soft x-ray exposure. Analysis of the x-ray absorption signal allows the complex

The study of three-dimensional (3D) magnetic nanostructures is a rapidly growing research area [1][2][3][4] due to potential technological applications 5,6 and emerging fundamental physics driven by non-trivial geometry and topology [7][8][9] , as well as the frustration that can arise due to interaction between 3D nanoelements [10][11][12][13][14] .Advances in theory have shown that curvature and torsion can yield additional energy terms in the form of effective Dzyaloshinskii-Moriya and effective anisotropy interactions [15][16][17] .Such interactions can lead to the stabilisation of topological spin textures [18][19][20] without the need for multilayer systems and can also yield novel dynamic phenomena such as domain wall automation 21 .Advancement in complex fabrication processes have allowed the realisation of many 3D geometries, including cylindrical magnetic nanowires 22 , rolled up membranes 23 , helical structures 24,25 and 3D artificial spin-ice structures 12 , by harnessing a range of self-assembly and lithographic methods.Next generation magnetic racetrack memories 5 rely upon 3D architectures and before such technologies can be realised, the detailed physics of domain wall topology, propagation and pinning needs to be understood in magnetic nanowires and elements of complex geometry.Advances in nanofabrication, theoretical modelling, and advanced characterization to validate such systems are prerequisite in that regard.
Of the many fabrication methodologies available, direct-write technologies are particularly interesting since they provide the most freedom in choice of geometry.Such technologies can harness either photons 26 or electrons 27,28 to generate the desired 3D geometry.For example, focussed electron beam induced deposition (FEBID) has been used to realise magnetic nanowires with transfer of domain walls from a planar substrate to an angled 3D nanowire 29 and exotic double helix structures which generate topological defects in the stray field 9 .Two-photon lithography (TPL) is a methodology whereby 3D nanostructures can be written by design within a suitable negative-tone photoresist by scanning a tightly focused laser through the resist to achieve the desired geometry 26 .By combining the technique with deposition technologies, it has been used to create bucky ball structures 30,31 , magnetic nanowires 11 , 3D artificial spin-ice (3DASI) building blocks 32 and arrays 10,12 .To characterize 3DASI array systems, magnetic force microscopy (MFM) was recently used to directly image the propagation of monopoles across the lattice 12 and to image the demagnetised state, suggesting relaxation into an exotic magnetic charge crystal.However, a key limitation of MFM is the requirement to physically access the surface topography to obtain accurate magnetic information, a challenging feat for any 3D lattice.The resolution of MFM depends upon the lift height which is usually limited to 50 -100 nm.It is therefore expected that advanced characterization techniques using polarized x-ray spectromicroscopies for tomographic reconstructions, with sub-50nm resolution, will become important in measuring next-generation 3D magnetic nanostructures 1,2,9,33,34 .
In this article we develop a new fabrication process that yields suspended 3DASI systems over an aperture.This allows measurement of full lattices with optical access to all nanowires without any need for tilt or rotation, whilst also eliminating any sheet film under the 3D nanostructure, in principle allowing the ordering to be determined.The element specific 3D geometric cross-section of underlying nanowires is determined, and x-ray magnetic circular dichroism (XMCD) shows evidence of a magnetic signal, allowing the magnetic texture upon a single sub-lattice to be reconstructed.
TPL is used to realise a diamond-bond polymer lattice over the exposed corner of a 50 μm x 50 μm Si aperture (Silson TEM-200-0.05-aperture).Crucially, the use of a dip-in TPL technique, allows the structure to be firmly anchored upon a large region of Si substrate, providing support for the suspended lattice region.Figure 1 shows a schematic of the fabrication process.The Si substrate is first cleaned in acetone and isopropyl alcohol (IPA), then carefully dried using compressed air (Figure 1a).A negative tone photoresist (IP-dip, Nanoscribe) is drop-cast onto the Si substrate and loaded into a TPL apparatus (Figure 1b).A diamond-bond lattice, one unit cell in height (approximately 2.3 μm), is written across each corner of the aperture (Figure 1c and Figure 1d) after which the sample is developed in propylene glycol monomethyl ether acetate (PGMEA), rinsed in IPA and then carefully dried using compressed air (Figure 1e). Figure 1f shows a schematic of a final structure with sub-lattice layers labelled SL1 -SL4.The SL1 nanowire layer is the upper surface termination and consists of coordination two and coordination four vertices.Layers SL2 and SL3 are comprised entirely of coordination four vertices.The SL4 wire layer is akin to SL1 with alternating coordination two and coordination four vertices.
Two sample sets were produced to investigate the extent to which a lattice can be suspended over an aperture.In sample set A, TPL was used with piezoelectric stages, scanning the sample with respect to the point of focus and only with an exposure of sub-lattices SL1 and SL2.In the second sample set, galvanometric mirrors were used to steer the laser focus with respect to the sample, with full exposure of sub-lattices L1-L4.Both sample sets were then subject to a tri-layer deposition, Al (4 nm) / Ni81Fe19 (43 nm) / Al (3 nm), to place a protected magnetic coating onto the polymer nanowires within the lattice (Figure 1f).Deposition of the stack was performed using a thermal evaporator operating at pressure 3 x 10 -7 mbar.A crystal quartz monitor present during evaporation measured the deposition thickness which was later confirmed with atomic force microscopy measurements.Sample set B was subject to an oxygen plasma step to further reduce the thickness of the underlying polymer.As shown previously [10][11][12]26 , the realised diamond lattice yields an array of single-domain magnetic nanowires that exhibit Ising-like behaviour.
Sample set A was subject to scanning transmission x-ray microscopy (STXM) at Diamond Light Source, beamline I08 and sample set B, subject to full-field transmission soft x-ray microscopy (TXM) at the Mistral beamline at ALBA.Prior to data collection at ALBA, x-ray absorption spectra (XAS) were obtained for each sample, and the photon energies corresponding to the L3 and L2 peaks of Fe were identified.The samples were first measured in their original as-deposited state.Subsequently, a field of approximately 100 mT was applied using an ex-situ permanent magnet.The experimental setup at the ALBA beamline was such that the more convenient measuring protocol was fixing the x-ray beam polarization (to circular left) and acquiring images at absorption edges with opposite dichroic contribution in order to extract the magnetic contrast 35 .Approximately 300 images were captured at both Fe L3 and Fe L2 photon energies.These images were aligned and normalized against a flat field image.Flat field images, obtained without a sample, were systematically acquired immediately before or after sample images to account for any variations in the x-ray illumination intensity and detector efficiency.This process enabled accurate analysis focused on genuine sample features.Normalised images were converted to optical density (OD) before an XMCD signal was calculated using: where  ',)* is the OD image at the Fe L3 photon energy and  .,)* is the OD image at the Fe L2 photon energy.
STXM was performed at Diamond Light Source I08 beamline.Initially, XAS were obtained by scanning across the Ni-and Fe-L2,3 photon energies allowing for the identification of the specific L2,3 edge photon energies associated with each sample.Subsequent data collection involved capturing image stacks using both left-and right-circularly polarised light over the pre-absorption and absorption edges within the energy ranges of Ni (845 -885 eV) and Fe (700 -723 eV).Optical Density images were obtained from the images by using: where I0 is the incident photon intensity, determined from sample-free regions of interest, and I is the transmitted intensity.Fe and Ni thickness maps were obtained by analysis of XAS images obtained using STXM at Diamond Light Source and by using the aXis2000 software package 36 .Each thickness map was obtained by taking the difference between the optical density image at the pre-edge absorption energy and the relevant resonance absorption peak.To analyse the XAS spectrum and estimate the sample thickness, the density and chemical composition of the material are required.
Using the atomic scattering factors available in the Henke tables 37 , the absolute thickness can in principle be estimated.However, in this work oxidation limited the extent to which overall chemical composition and density could be estimated and thus we only present the relative change in thickness, sufficient to estimate the wire cross-sectional geometry.XMCD measurements were also attempted using STXM by measurement of images for left-and right-circular polarisation, alignment and subsequent subtraction.
Sample set A was fabricated using a piezo-mode, to provide longer exposures and aid in adhering the written polymer to the substrate surrounding the aperture.Such samples provide maximum stability of the suspended lattice providing initial feasibility of the transmission-based experiments.Figure 2a shows a scanning electron microscopy (SEM) of the 3DASI lattice, with Figure 2b showing an image taken at 45⁰ tilt.The individual nanowires are found to have widths of 301 ± 7 nm, length of 1 µm and average thickness of wires is approximately 1 µm.Representative XMCD images, taken at the Ni L2 and L3 edges are shown in Figure S1a and S1b, respectively, for the region outlined in Figure 2a (Dashed lines).Bands of contrast can be seen upon individual nanowires.However, we note that the apparent contrast does not invert between the L2 image and L3 image, suggesting this contrast is not magnetic in origin but likely an artefact.Though, XMCD contrast is absent, transmission-based experiments allow the intriguing possibility to explore the 3D cross-section of the nanowires in these samples.Previous work has hinted that the wires have a novel crescent-shaped cross-section 10 .Figure 2c and 2d show thickness maps of the Ni and Fe components of the magnetic material upon the lattice respectively.Both show that the magnetic material is uniform across much of the lattice with a region of decreased thickness found at the intersection of SL1 and SL2.In this location the measured optical density drops by 40%.This can be explained with SEM measurements which shows that the suspended lattice tilts slightly into the aperture, which combined with the evaporation at normal incidence to the sample will result in a change in deposition thickness transverse to the tilt axis.Extracting line profiles across the wire width allows the cross-sectional thickness variation to be determined, as shown in Figure 2e.The profile shows a graded thickness as previously hinted by SEM imaging 10 .When considering the cross-sectional geometry of a TPL voxel, which has an elliptical shape 26 , superposition of a graded NiFe thickness yields wires of crescent-shaped cross-section, as shown in Figure 2e inset.Magnetic nanowires with crescent-shaped cross-section are expected to host domain walls with perturbed spin texture, due to the curvature yielding effective anisotropy and Dzyaloshinskii-Moriya energies 16 .Overall, initial STXM studies at Diamond Light Source on sample set A provided initial feasibility of measurement and gave insight into the physical cross-section of the nanowires.
Sample set B was fabricated with galvanometric mirrors, which reduced the exposure dose of the lattice.A key advantage of this approach is a reduced thickness of the polymer nanowires.Exposure to an oxygen plasma further reduces the polymer thickness.A SEM image of a suspended 3DASI from sample set B is shown in Figure 3a, with high magnification images shown in Figures 3b and 3c.
Nanowires were found to have widths of approximately 220 ± 6 nm and lengths 1 µm.Atomic force microscopy (AFM) was used to measure surface topography as shown in Figure 3d.The 3DASI in this sample set comprises of four sub-lattice layers designated SL1 through to SL4, as depicted in Figure 3c.The average thickness of the nanowires for this sample set was found to be approximately 810 ± 18 nm which lower than those of sample set A.
The transmission (T) of x-rays through the polymer layer can be determined using 37 : where d is the thickness of the layer, with density n, and atomic photo-absorption cross section µa is defined as where r0 is the classical electron radius, λ is the wavelength, and f2 is the imaginary component of the atomic scattering factor.Based on the Henke tables, estimates of x-ray transmission through the polymer for sample set B suggested a transmission of 65% at the Ni L3 edge photon energy and 51% at the Fe L3 edge photon energy, as shown in Figure 3e (Black line).We calculate that a 100 nm thick Si3N4 membrane has a transmission of approximately 80-85 %, at the Fe L3 edge photon energy.The increased polymer thickness present in our structures adds substantially to the non-magnetic background and will therefore reduce the signal-to-noise of XMCD measurements.In an attempt to circumvent this problem, a sample set was fabricated with increasing oxygen plasma exposure time.
The oxygen plasma selectively removes the carbon-based polymer, reducing its thickness and increasing soft x-ray transmission as shown in Figure 3e and Figure 3f.In these structures, the process appears to be self-limiting, with an exponential-like decay in polymer thickness.Previous work on simple polymer-based scaffolds has suggested a similar trend whereby the etch rate was found to be high (~12nm per minute) in the first 2 minutes, to almost no observable etching after 6 minutes 39 .We note that in our structure the stray field from the magnetic coating may also shield structures from the plasma, reducing the overall etching performance.
Sample set B were measured using in-house magneto optical Kerr effect (MOKE) magnetometry prior to x-ray microscopy measurements.MOKE loops upon the Si substrate that surrounds the aperture yielded a hysteresis loop with a coercive field of μ0HC = 0.6 mT as-deposited and 0.5 mT after a 30 minute plasma exposure, as shown in Figure S2 of Supplementary Material.The slightly increased coercivity is likely to be due to the substrate roughness or slight oxidation but is still consistent with the range measured previously 38 for evaporated Ni81Fe19.Figure 4a shows XAS taken at the Fe L3 edge upon samples with varying oxygen plasma exposure, with full spectra shown in Figure S3 of Supplementary Material.The sample with no oxygen plasma exposure shows a peak at 707.5 eV indicating metallic Ni81Fe19.The presence of a shoulder at ~709 eV suggests some oxidation 40 , despite a capping layer.Measurement of samples with increasing oxygen exposure, yields more evidence of a multiplet structure with increasing peak intensity at ~709 eV. Figure 4a inset shows that the ratio of Fe peak to Fe3O4 peak decreases with increasing oxygen plasma exposure time.Overall, these results suggest that samples with intermediate oxygen plasma time will have the best balance of reduced polymer thickness but with a large volume fraction of metallic Ni81Fe19.Specifically, for the 60-minute oxygen plasma exposure the polymer thickness is reduced by ~10%.This should yield an improved transmission whilst maintaining a Fe / Fe3O4 L3 peak ratio of 0.95.
Figure 4b shows an XAS optical density image taken at the Fe L3 edge, upon a sample that was exposed to an oxygen plasma for the optimal 60 minutes.A crucial uncertainty with respect to such samples, was the extent to which the 3DASI structure, which is suspended, fabricated using Galvanometric mirrors with reduced anchoring, and subject to an oxygen plasma, would remain stable.Analysis of multiple images taken over several hours, see Supplementary Video 1, shows little movement or distortion of the lattice.Some regions within Figure 4b can be clearly seen to have higher x-ray absorption.In many cases, these areas are correlated with overlap in lower structures.
Figure 5 shows XMCD images using TXM, of a lattice subject to a 60-minute oxygen plasma exposure, in an as deposited state (Figure 5a) and after application of a 100 mT field (Figure 5b).Apparent contrast is present in the images, with dark regions particularly noticeable at vertices.Close inspection of these regions suggests that this contrast is not of magnetic origin, but due to overlapping features.
To carefully inspect the measurement for evidence of magnetism, non-overlapping regions were found and chains, connected wires on a specific sub-lattice, were identified for SL1, SL2 and SL3, as shown in Figure S4 of Supplementary Material.The average XMCD signal for Fe L3 across the central region of the wire, where there is negligible structural background, was measured.This was then plotted for each of the three wire sublattices for the as-deposited state and after application of 100 mT magnetic field, as shown in Figure 5c and 5d.Previous studies have shown the magnetic configuration that would be expected after application of a saturating field 12 .In-plane saturation along each of the sub-lattices will yield a net magnetisation component parallel to the field.However, since each wire along a given sub-lattice has an alternating ± 35.25° angle, out of the substrate plane and since XMCD measurements are sensitive to the magnetisation component along the photon propagation direction, for a saturated sample we expect to see alternating contrast as depicted in Figure S6 of Supplementary Material.Examination of the SL1 chain contrast shown in Figure 5c yields inconclusive results.Since the uppermost layer is most susceptible to artefacts due to overlap, only short chains can be identified, and these do not show a difference in trend when comparing configurations before and after field application.This suggests any XMCD signal upon the SL1 sublattice is below the noise floor of the measurement.Analysis of data upon SL2, presented in Figure 5d is more intriguing.The relative contrast, wire-to-wire, is different before and after application of the magnetic field.Notably, the chain data after application of a magnetic field takes the expected form with alternating contrast, as depicted in Figure S6 of Supplementary Material.The XMCD signal is weak, at around 4%, likely due to a reduced magnetic moment driven by oxidation.An alternative analysis that can be performed is to inspect the magnitude of the contrast for wires in adjacent chains.
Here, we expect wires with positive and negative magnetisation projection onto k to have distinct values.Figure 5e shows the XMCD signal for the two sets of wires before and after application of a field.Before application of the field, the average XMCD value for both sets of wires are found to be within 0.5 %, suggesting a net out-of-plane magnetisation.After application of the field, both SL2 and SL3 are found to have a difference of approximately 4%, consistent with the previous analysis and suggesting the presence of a weak magnetic signal.However, only SL2 has distinct populations of XMCD signal, for which there is no overlap within 2σ, suggesting high confidence of magnetic contrast.Plotting the magnetisation of the SL2, as shown in Figure 5f also shows that the measured configuration is consistent with the direction of external field, providing additional confidence.We note that similar analysis on SL3 shows weaker evidence of magnetic contrast, as is shown in Figure S7 and Figure S8 of Supplementary Material.Though there is a difference in mean XMCD signal between upwards and downward wires, there is strong overlap in the two populations.We note that it is possible for a small drift in focus to account for the small XMCD signals observed on the SL2 and SL3 sub-lattices but that this would impact all sub-lattices, whereas for SL1 (Fig 5a ), there is clearly no change in trend before and after field.Additional comparative analysis of wire widths (SL1, SL2, SL3), shown in Figure S9 of Supplementary Material, between XAS images of pre-and post-field application revealed consistent measurements within the margin of error, suggesting negligible drift in focus.
A key question is why only specific sub-lattices within the structure show evidence of magnetic contrast.The oxygen plasma exposure is expected to be uniform across ~100 mm diameter.However, the extent to which the plasma can penetrate a 50 µm x 50 µm aperture is less certain.Furthermore, the stray field lines from the NiFe coating may partially shield the lattice, particularly the lower layers.This may impact both the extent to which different sub-lattices have oxidised NiFe as well as resulting in a gradient in polymer thickness when going from SL1 to SL4 sub-lattices.Overall, this is likely to lead to a trend whereby SL1 has the most polymer removed but also has the most prominent reduction in magnetisation due to oxidation.At the other extreme, SL3 and SL4 are likely to have a higher magnetisation but the least polymer removed, yielding a lower signal-to-noise in XMCD measurements.The intermediate SL2 sub-lattice is then likely to be optimal in terms of magnetisation and polymer removal.

Conclusions
In conclusion, a 3DASI lattice has been fabricated over an aperture using two-photon lithography, deposition and oxygen plasma exposure.The 3D lattice is found to be stable when subject to repeated soft x-ray exposure.Plasma exposure of the polymer scaffold improved x-ray transmission through the structure, yielding greater signal than would otherwise be seen.XAS data is used to extract the cross-section of the magnetic nanowire which is found to take a novel crescent-shaped geometry.XMCD measurements suggest a signal can be measured on the buried sub-lattices, hinting at the expected configuration after an applied field.Minor adjustments in the fabrication procedure, by using a shorter wavelength laser 41 , are expected to reduce the need for an oxygen plasma, and when combined with optimised beamline measurement protocols are expected to provide uniform magnetic contrast across all lattice layers and with improved signal to noise.

Figure 1 :
Figure 1: Fabrication methodology for suspended 3DASI.(a) A Si substrate with 50 µm x 50 µm aperture is cleaned.(b) Surface of Si substrate is coated with negative-tone resist (IP-DIP).(c-d) Two photon lithography is used to polymerise the resist in a diamond bond lattice geometry (12 µm x 30 µm x 2.3 µm) over the aperture corner.(e) Sample development and cleaning in IPA removes unexposed resist and reveals solid polymer scaffold structure.Permalloy (Ni81Fe19) is deposited onto the upper surface of lattice via thermal evaporation resulting in a suspended 3DASI structure.(f) Schematic showing the final structure with individual sub-lattices SL1, SL2, SL3 and SL4, upon the 3DASI.

Figure 2 :
Figure 2: Determination of magnetic nanowire cross-section (a) Scanning electron microscopy image of sample measured at Diamond Light Source.The region where XMCD was measured is outlined by the dotted line.Scale bar shown is 5 μm.(b) SEM image of 3D ASI viewed from 45⁰ tilt.Measurements annotated show regions of wires measured for thickness measurements.A trigonometry calculation was used to transform measured values to account for tilt of image.An average thickness of 1.03 µm is obtained.Scale shown is 1 μm.(c) Heat map of Ni thickness.(d) Heat map of Fe thickness.(e) Average Ni and Fe cross-sectional thickness profile, across 16 measured lattice nanowires.Inset: Elliptical cross-section of a TPL voxel (yellow) and the crescent shaped cross-section of NiFe (Grey) obtained when adding a graded thickness as suggested by the measured thickness heat maps.

Figure 3 :
Figure 3: A multiple layer suspended 3DASI lattice.(a) Scanning electron microscopy image (SEM) of 3DASI lattice suspended over an aperture corner.(b) Zoomed SEM image of the upper surface.(c) Top-view SEM of the suspended lattice.Sub-lattices of different depth are labelled SL1 (Highest), SL2, SL3 and SL4 (Lowest).(d) Atomic force microscopy image for region of suspended 3DASI lattice.(e) Calculated transmission of x-rays through PMMA (C5H8O2) for different values of polymer thickness, as indicated in legend.The Fe and Ni L3 edges are shown at the top of the panel.Transmission calculations were carried out using centre of x-ray optics online tool with PMMA as approximate resist material.(f) Average polymer scaffold thickness measured via tilted SEM micrographs plotted against

Figure 4 :
Figure 4: Determining optimal processing parameters for soft x-ray microscopy (a) Fe L3 spectra for samples of increasing oxygen exposure time.Each spectrum is the average across wires on the lattice.The spectra have been artificially offset in the vertical axis for clarity.The Fe L3 absorption edge present an oxidised component that appears as a shoulder peak at 709 eV with intensity dependent on the oxygen plasma exposure time.Inset shows ratio of metallic peak to oxide peak, as a function of plasma exposure time.(b) Optical density image at the Fe L3 photon energy of a suspended 3DASI lattice.

Figure 5 :
Figure 5: Measurement of magnetic contrast upon a suspended 3D artificial spin-ice.(a) X-ray Magnetic Circular Dichroism (XMCD) image of lattice in an as-deposited state and (b) post 100 mT applied field, in direction indicated by white arrow.(c) Normalised XMCD signal for wire chains in asdeposited state (Grey circles) and after application of 100mT field (Blue circles), for the SL1 sub-lattice.(d) Normalised XMCD signal for wire chains in as-deposited state (Grey circles) and after application of 100mT field (Blue circles), for the SL2 sub-lattice.(e) Extracted XMCD contrast for nanowires upon

Figure S2 :
Figure S2: Longitudinal magneto-optical Kerr effect loops from the thin-film section of substrate, for sample not exposed to oxygen plasma (Black line) and for sample exposed to oxygen plasma for 0.5 hours.

Figure S3 :
Figure S3: Experimental Fe L2,3 x-ray absorption spectra taken at ALBA synchrotron.Samples were subject to varied time in an oxygen plasma to remove polymer scaffold beneath deposited material.The pre-edge absorption can be attributed to the underlying polymer.

Figure S4 :
Figure S4: X-ray absorption images.Chains of individual wires with no overlap have been identified and labelled for (a) SL1 layer, (b) SL2 layer.(c) SL3 layer.

Figure S6 :
Figure S6: (a) Diagram showing magnetisation arrangement within a chain of wires, after in-plane saturation.(b) Schematic of x-ray magnetic circular dichroism (XMCD) signal shown for the magnetisation arrangement shown in a. (c) Graph showing the expected XMCD trend for wire chains post-saturation.

Figure S7 :
Figure S7: Measured normalised x-ray Magnetic Circular Dichroism (XMCD) signal for wire strings for both as-deposited and post-saturation for the SL3 sublattice.

Figure S8 :
Figure S8: Measured normalised x-ray magnetic circular dichroism (XMCD) signal plotted for interchain comparison for both as-deposited and post-saturation for the SL3 sublattice.Average XMCD signal shown with blue dotted line.Red dashed line shows two standard deviations of mean for each population.

Figure S9 :
Figure S9: (a) Aligned XAS Fe L3 image of measured lattice, before application of field.(b) Aligned XAS Fe L3 image of measured lattice, post field application.Scale bar shown is 2 μm.A total of 50 wire width measurements were taken across both images at same locations for each sublattice layer.(c) Mean wire width of each sublattice layer for pre-and post-magnetic field images with standard error shown as error bar.