In recent years the intermetallic alloys of Fe and Sn have gained significant interest due to a rich variety of magnetic properties present in these materials. The crystal Fe3Sn2 is a frustrated ferromagnet, while the crystallographically similar FeSn, which differs only by the stacking sequence of its Fe-containining kagome and stanene layers, is an antiferromagnet. Thin-film growth techniques such as magnetron sputtering allow for these different stoichiometric compositions to be grown through adjustments of the rate of deposition of the individual Fe and Sn sources, while all other conditions remain constant. Here, we report the production of high quality epitaxial thin films of Fe_3Sn_2 and FeSn on sapphire with a Pt seed layer, as well as a mixed phase containing intergrowths of both crystals, all of which we have characterized using both X-ray and four-dimensional scanning transmission electron microscopy (4D-STEM) methods. The resulting crystallographic phase content is compared to the results of magnetization measurements, with correspondence between the predicted ferromagnetic phase content and the resulting magnetization. Further magnetic properties of these films can then also be compared, leading to the discovery of a unique behavior in the temperature dependent coercivity within highly mixed phase alloys, a feature that is absent in either pure Fe3Sn2 and FeSn.

Focused electron beam induced deposition (FEBID) is an additive manufacturing technique uniquely suited for fabricating nanoscale 3D prototypes for a range of applications, including spintronic devices. However, the variation of growth dynamics associated with electron beam translation and sample interaction volumes results in structures with non-uniform composition when fabricating intricate 3D geometries. Herein, we measure changes in atomic composition and corresponding changes in magnetic induction in 3D ferromagnetic nanostructures with overhanging elements, e.g. bridges or arches. To investigate the effects of electron beam translation, we fabricated 41 Co and Fe nanowire (NW) structures with growth angle relative to the optic axis varying from 0° to 90°. The (scanning) transmission electron microscopy techniques of electron energy loss spectroscopy and off-axis electron holography were performed to map the NW elemental composition and magnetic induction as a function of NW growth angle. Comparison of the results reveals a reduction in metal content with increased oblique growth angle in FEBID NWs. The magnitude of metal content reduction can be tuned by controlling electron beam parameters, and ferromagnetic NWs with approximately equal metal content at growth angles from 0° to 60° were fabricated by using the lowest viable electron beam voltage and the highest viable beam current to reduce the interaction volume and increase the metal content, respectively.

Magnetic skyrmions are topologically protected spin textures that can act as reconfigurable nanoscale information carriers. In synthetic antiferromagnets, interlayer exchange coupling provides a control parameter beyond the interfacial Dzyaloshinskii-Moriya interaction and magnetic anisotropy. Here we engineer a synthetic antiferromagnet of two chemically distinct ferromagnets, CoB and CoFeB, in which the external field and interlayer exchange act asymmetrically on the sublattices. Their competition, acting as an effective field, gives rise to two skyrmion families in different field regimes: conventional-polarity skyrmions at large fields, and inverse-polarity skyrmions at smaller fields, where the effective field reverses sign. Using element-resolved X-ray magnetometry, correlative magnetic force and Lorentz transmission electron microscopies, and micromagnetic modelling, we show that all textures reside solely in the CoFeB layers, driven by a Ruderman-Kittel-Kasuya-Yosida exchange field from the CoB layers. This effective-field route enables programmable three-dimensional spin textures with layer-selected polarity for skyrmion-based computing.

Stabilizing magnetic skyrmions is a critical issue in spintronics, impacting data storage and computing. This study investigates skyrmion and skyrmionium phenomena within a hexagonal array of curved nanomagnets. Utilizing atomistic calculations, micromagnetic simulations, and experimental methods such as magnetic force microscopy and electron holography, we analyze the interplay between magnetic parameters, curvature, and the interfacial Dzyaloshinskii-Moriya interaction (iDMI) in the formation of these structures. We observed that isolated skyrmions and mixed skyrmionic phases can spontaneously form in a symmetric Pt/Co/Pt multilayer curved nanomagnet matrix without external fields at room temperature. Our findings highlight the considerable influence of geometric curvature on iDMI, providing insights for engineering skyrmionic configurations. This research enhances our understanding of nanomagnetism and contributes to the advancement of skyrmion-based technologies.

Chiral magnetic textures are key for the development of modern spintronic devices. In multilayered thin films, these are typically stabilized via the interfacial intralayer Dzyaloshinskii-Moriya interaction (DMI). Additionally, it has been recently observed that DMI may also promote vector spin chirality along the third dimension, coupling spins in different magnetic layers via nonmagnetic spacer layers, an effect referred to as interlayer DMI (IL-DMI). This interaction holds promise for 3D nanomagnetism, from the creation of 3D spin structures such as hopfions to new forms of magnetic functionality in the vertical direction via remote control of chiral spin states. In this work, we provide direct experimental evidence that the in-plane vector spin chirality of magnetic textures within a ferromagnetic layer can be controlled via the net out-of-plane spin configuration of an adjacent one. Both ferromagnetic layers form part of a synthetic antiferromagnet, previously shown to have IL-DMI. This in-plane vector chirality dependence on the out-of-plane configuration of another layer implies that the overall scalar spin chirality is preserved when computed across layers. We draw these conclusions from a combination of magnetic x-ray scattering and imaging experiments, complemented by various simulations. These findings thus uncover a type of chiral interlayer interactions, which can lead to the formation of intricate spin states across a metallic interface, demonstrating other ways to control magnetic chirality in three dimensions.

The discovery of quantum emitters (QEs) in two-dimensional (2D) materials has triggered a surge of research to assess their suitability for quantum photonics. Although position-controlled QEs are routinely fabricated using static strain gradients, the use of dynamic strain fields to control the brightness of QEs has not been explored yet. Here, we address this challenge by introducing a novel device in which WSe2 monolayers are integrated onto piezoelectric pillars that provide both static and dynamic strains. The static strains are first used to induce the formation of QEs, while their energy and brightness are then controlled via voltages on piezoelectric pillars. Numerical simulations show that these effects are due to a strain-induced modification of the confining-potential landscape, which leads to a net redistribution of excitons among the different QEs. Our work provides a method to dynamically control the energy and brightness of QEs in 2D materials.

Experimental techniques for the characterization of three-dimensional (3D) magnetic spin structures are required to advance the performance of nanoscale magnetic technologies. However, as component dimensions approach the nanometer range, it becomes ever more challenging to analyze 3D magnetic configurations quantitatively with the required spatial resolution and sensitivity. Here, we use off-axis electron holography and model-based iterative reconstruction to reconstruct the 3D magnetization distribution in an exemplary nanostructure comprising an L-shaped ferromagnetic cobalt nanowire fabricated using focused electron beam induced deposition. Our approach involves using off-axis electron holography to record tomographic tilt series of electron holograms, which are analyzed to reconstruct electron optical magnetic phase shifts about two axes with tilts of up to ±60∘. A 3D magnetization vector field that provides the best fit to the tomographic phase measurements is then reconstructed, revealing multiple magnetic domains in the nanowire. The reconstructed magnetization is shown to be accurate for magnetic domains that are larger than approximately 50 nm. Higher spatial resolution and improved signal-to-noise can be achieved in the future by using more specialized electron microscopes, improved reconstruction algorithms, and automation of data acquisition and analysis.

This work presents a detailed analysis of the performance of X-ray magnetic circular dichroism photoemission electron microscopy (XMCD-PEEM) as a tool for vector reconstruction of magnetization. For this, 360° domain wall ring structures which form in a synthetic antiferromagnet are chosen as the model to conduct the quantitative analysis. An assessment is made of how the quality of the results is affected depending on the number of projections that are involved in the reconstruction process, as well as their angular distribution. For this a self-consistent error metric is developed which allows an estimation of the optimum azimuthal rotation angular range and number of projections. This work thus proposes XMCD-PEEM as a powerful tool for vector imaging of complex 3D magnetic structures.

In synthetic antiferromagnets (SAFs), antiferromagnetic (AFM) order and synthesis using conventional sputtering techniques is combined to produce systems that are advantageous for spintronics applications. Here we present the preparation and study of SAF multilayers possessing both perpendicular magnetic anisotropy and the Dzyaloshinskii-Moriya interaction. The multilayers have an antiferromagnetically aligned ground state but can be forced into a full ferromagnetic (FM) alignment by applying an out-of-plane field -100 mT. We study the spin textures in these multilayers in their ground state as well as around the transition point between the AFM and FM states at fields - 40 mT by imaging the spin textures using complementary methods: photoemission electron, magnetic force, and Lorentz transmission electron microscopies. The transformation into a FM state by field proceeds by a nucleation and growth process, where skyrmionic nuclei form and then broaden into regions containing a ferromagnetically aligned labyrinth pattern that eventually occupies the whole film. Remarkably, this process occurs without any significant change in the net magnetic moment of the multilayer. The mix of antiferromagnetically and ferromagnetically aligned regions on the micron scale in the middle of this transition is reminiscent of a first-order phase transition that exhibits phase coexistence. These results are important for guiding the design of spintronic devices whose operation is based on spin textures in perpendicularly magnetized SAFs.

The interlayer Dzyaloshinskii–Moriya interaction (IL-DMI) chirally couples spins in different ferromagnetic layers of multilayer heterostructures. So far, samples with IL-DMI have been investigated utilizing magnetometry and magnetotransport techniques, where the interaction manifests as a tunable chiral exchange bias field. Here, we investigate the nanoscale configuration of the magnetization vector in a synthetic anti-ferromagnet (SAF) with IL-DMI, after applying demagnetizing field sequences. We add different global magnetic field offsets to the demagnetizing sequence in order to investigate the states that form when the IL-DMI exchange bias field is fully or partially compensated. For magnetic imaging and vector reconstruction of the remanent magnetic states, we utilize x-ray magnetic circular dichroism photoemission electron microscopy, evidencing the formation of 360° domain wall rings of typically 0.5–3.0 μm in diameter. These spin textures are only observed when the exchange bias field due to the IL-DMI is not perfectly compensated by the magnetic field offset. From a combination of micromagnetic simulations, magnetic charge distribution, and topology arguments, we conclude that a non-zero remanent effective field with components both parallel and perpendicular to the anisotropy axis of the SAF is necessary to observe the rings. This work shows how the exchange bias field due to IL-DMI can lead to complex metastable spin states during reversal, important for the development of future spintronic devices.

The discovery of quantum emitters in two-dimensional materials has triggered a surge of research to assess their suitability for quantum photonics. While their microscopic origin is still the subject of intense studies, ordered arrays of quantum emitters are routinely fabricated using static strain-gradients, which are used to drive excitons toward localized regions of the 2D crystals where quantum-light-emission takes place. However, the possibility of using strain in a dynamic fashion to control the appearance of individual quantum emitters has never been explored so far. In this work, we tackle this challenge by introducing a novel hybrid semiconductor-piezoelectric device in which WSe2 monolayers are integrated onto piezoelectric pillars delivering both static and dynamic strains. Static strains are first used to induce the formation of quantum emitters, whose emission shows photon anti-bunching. Their excitonic population and emission energy are then reversibly controlled via the application of a voltage to the piezoelectric pillar. Numerical simulations combined with drift-diffusion equations show that these effects are due to a strain-induced modification of the confining-potential landscape, which in turn leads to a net redistribution of excitons among the different quantum emitters. Our work provides relevant insights into the role of strain in the formation of quantum emitters in 2D materials and suggests a method to switch them on and off on demand.

zero-temperature limit Paul G. Baity,1 Dmytro A. Bozhko,2 Rair Macêdo,1 William Smith,3 Rory C. Holland,1 Sergey Danilin,1 Valentino Seferai,1 Renju R. Peroor,2 Sara Goldman,2 Umberto Nasti,1, 4 Jharna Paul,1 Robert H. Hadfield,1 Stephen McVitie,3 and Martin Weides1 1)James Watt School of Engineering, Electronics & Nanoscale Engineering Division, University of Glasgow, Glasgow G12 8QQ, United Kingdoma) 2)Center for Magnetism and Magnetic Materials, Department of Physics and Energy Science, University of Colorado Colorado Springs, Colorado Springs, Colorado 80918, USA 3)SUPA, School of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, United Kingdom 4)Current affiliation: School of Engineering & Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, United Kingdom

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In Part I of this diptych, we outline the parallel mode of differential phase contrast (TEM-DPC), which uses real-space distortion of Fresnel images arising from electrostatic or magnetostatic fields to quantify the phase gradient of samples with some degree of structural contrast. We present an analysis methodology and the associated software tools for the TEM-DPC method and, using them together with numerical simulations, compare the technique to the widely used method of phase recovery based on the transport-of-intensity equation (TIE), thereby highlighting the relative advantages and limitations of each. The TEM-DPC technique is particularly suitable for in situ studies of samples with significant structural contrast and, as such, complements the TIE method since structural contrast usually hinders the latter, but is an essential feature that enables the former. In Part II of this work, we apply the theory and methodology presented to the analysis of experimental data to gain insight into two-dimensional magnetic phase transitions.

Ni45Fe55 has long been a high moment alternative for Ni80Fe20, which is commonly used in hard disk drive (HDD) read-write head design. In this paper we investigate the effect of ultra thin Ni79Fe21 seed layers on controlling the physical and magnetic behaviour of Ni45Fe55. Transmission electron microscopy (TEM) was used to observe grain size variation. Introducing a seed layer of 0.5 nm thickness reduced the average grain size diameter by over 80% to 2 nm. Diffraction analysis shows texture exists along the [010] direction for the unseeded and 0.25 nm seed layer films. The addition of the Ni79Fe21 seed layer reduces film texture. Bulk magnetic measurements showed seed layers improved uniaxial anisotropy, with decreasing easy axis coercivity HC, and an increase in the anisotropy field HK. The Fresnel mode of Lorentz microscopy was used to image micromagnetic behaviour during in situ magnetising experiments. The nano-scale visualisation of the magnetic structure allows for not only the mapping of hysteresis behaviour, but quantitative characterisation of the material in the form of magnetisation ripple. This was characterised in two ways; the ripple dispersion and wavelength. The addition of Ni79Fe21 seed layers acted to significantly reduce ripple wavelength and dispersion angle. The dramatic effect of seed layer addition suggests that the ultra-thin film is a good candidate for controlling both the physical and magnetic properties of Ni45Fe55 films, whilst maintaining a high magnetic moment density.