Holographic imaging of antiferromagnetic domains with in-situ magnetic field

Lensless coherent x-ray imaging techniques have great potential for high-resolution imaging of magnetic systems with a variety of in-situ perturbations. Despite many investigations of ferromagnets, extending these techniques to the study of other magnetic materials, primarily antiferromagnets, is lacking. Here, we demonstrate the first (to our knowledge) study of an antiferromagnet using holographic imaging through the 'holography with extended reference by autocorrelation linear differential operation' technique. Energy-dependent contrast with both linearly and circularly polarized x-rays are demonstrated. Antiferromagnetic domains and topological textures are studied in the presence of applied magnetic fields, demonstrating quasi-cyclic domain reconfiguration up to 500 mT

Holographic imaging of antiferromagnetic domains with in-situ magnetic field

Lensless coherent x-ray imaging techniques have great potential for high-resolution imaging of magnetic systems with a variety of in-situ perturbations. Despite many investigations of ferromagnets, extending these techniques to the study of other magnetic materials, primarily antiferromagnets, is lacking. Here, we demonstrate the first (to our knowledge) study of an antiferromagnet using holographic imaging through the "holography with extended reference by autocorrelation linear differential operation" technique. Energy-dependent contrast with both linearly and circularly polarised x-rays are demonstrated. Antiferromagnetic domains and topological textures are studied in the presence of applied magnetic fields, demonstrating quasi-cyclic domain reconfiguration up to 500 mT.Comment: 14 pages, 6 figure

Room-temperature in-plane ferromagnetism in Co-substituted Fe 5 GeTe 2 investigated by magnetic x-ray spectroscopy and microscopy

The exploration of two-dimensional (2D) van der Waals ferromagnets has revealed intriguing magnetic properties with significant potential for spintronics applications. In this study, we examine the magnetic properties of Co-doped Fe5GeTe2 using x-ray photoemission electron microscopy (XPEEM) and x-ray magnetic circular dichroism (XMCD), complemented by density functional theory calculations. Our XPEEM measurements reveal that the Curie temperature ( TC) of a bilayer of (CoxFe 1−x) 5−δGeTe2 (with x = 0.28) reaches ∼300 K—a notable enhancement over most 2D ferromagnets in the ultrathin limit. Interestingly, the TC shows only a small dependence on film thickness (bulk TC≈340 K), in line with the observed in-plane (IP) magnetic anisotropy and robust IP exchange coupling. XMCD measurements indicate that the spin moments for both Fe and Co are significantly reduced compared to the theoretical values. These insights highlight the potential of Co-doped Fe5GeTe2 for stable, high-temperature ferromagnetic applications in 2D materials

Spatially reconfigurable antiferromagnetic states in topologically rich free-standing nanomembranes

Antiferromagnets hosting real-space topological textures are promising platforms to model fundamental ultrafast phenomena and explore spintronics. However, they have only been epitaxially fabricated on specific symmetry-matched substrates, thereby preserving their intrinsic magneto-crystalline order. This curtails their integration with dissimilar supports, restricting the scope of fundamental and applied investigations. Here we circumvent this limitation by designing detachable crystalline antiferromagnetic nanomembranes of α-Fe2O3. First, we show—via transmission-based antiferromagnetic vector mapping—that flat nanomembranes host a spin-reorientation transition and rich topological phenomenology. Second, we exploit their extreme flexibility to demonstrate the reconfiguration of antiferromagnetic states across three-dimensional membrane folds resulting from flexure-induced strains. Finally, we combine these developments using a controlled manipulator to realize the strain-driven non-thermal generation of topological textures at room temperature. The integration of such free-standing antiferromagnetic layers with flat/curved nanostructures could enable spin texture designs via magnetoelastic/geometric effects in the quasi-static and dynamical regimes, opening new explorations into curvilinear antiferromagnetism and unconventional computing

Stabilizing and tuning topological antiferromagnetic spin textures in α-Fe2O3 based heterostructures

Topological textures, such as skyrmions, merons, antimerons, and bimerons within antiferromagnetic materials, offer significant potential for advancing spintronics applications due to their secure and high-speed information carrying capabilities. However, experimental progress in this area is hindered by challenges stemming from the inherent magnetic compensation in antiferromagnets, which obstruct direct manipulation and visualization of these textures using conventional magnetic sensing methods. In this study, we applied advanced X-ray imaging techniques, specifically X-PEEM, to explore and successfully demonstrate the stabilization of nanoscale topological textures at room temperature through the magnetic phase transition within the archetypal antiferromagnetic oxide, hematite (α-Fe2O3). Despite the promising spin configurations achieved, they are intricately woven into a non-uniform antiferromagnetic background, posing challenges for targeted manipulation and study. We overcame these experimental challenges by coupling the topologically-rich antiferromagnetic layer to a ferromagnetic layer. This integration leverages the advantageous magnetic properties of each material through precisely engineered bulk and interfacial interactions within α-Fe2O3|Co|Pt heterostructures. These structures seamlessly merge the control and readability benefits of ferromagnetic layer with the inherent robustness of antiferromagnetic materials, opening new avenues in the exploration of skyrmionics. We observe that each antiferromagnetic spin configuration leaves a distinct imprint on the adjacent ferromagnetic layer through interfacial exchange, resulting in hybrid of antiferromagnetic and ferromagnetic topological structures. Furthermore, we identify a polar magnetic interface via X-ray absorption dichroic spectra. Finally, by combining temperature variations with a series of magnetic field pulses, we successfully create isolated magnetic bimerons (topological counterpart of skyrmions) in a nearly uniform background for the first time. Our breakthroughs underscore the potential of these heterostructures as an ideal platform for studying the formation and evolution of hybrid topological structures, paving a promising path toward the development of resilient skyrmionbased devices

Spin pumping through nanocrystalline yopological insulators

The topological surface states (TSSs) in topological insulators (TIs) offer exciting prospects for dissipationless spin transport. Common spin-based devices, such as spin valves, rely on trilayer structures in which a non-magnetic (NM) layer is sandwiched between two ferromagnetic (FM) layers. The major disadvantage of using high-quality single-crystalline TI films in this context is that a single pair of spin-momentum locked channels spans across the entire film, meaning that only a very small spin current can be pumped from one FM to the other, along the side walls of the film. On the other hand, using nanocrystalline TI films, in which the grains are large enough to avoid hybridization of the TSSs, will effectively increase the number of spin channels available for spin pumping. Here, we used an element-selective, x-ray based ferromagnetic resonance technique to demonstrate spin pumping from a FM layer at resonance through the TI layer and into the FM spin sink

Spin Pumping Through Nanocrystalline Topological Insulators

Abstract The topological surface states (TSSs) in topological insulators (TIs) offer exciting prospects for dissipationless spin transport. Common spin-based devices, such as spin valves, rely on trilayer structures in which a non-magnetic (NM) layer is sandwiched between two ferromagnetic (FM) layers. The major disadvantage of using high-quality single-crystalline TI films in this context is that a single pair of spin-momentum locked channels spans across the entire film, meaning that only a very small spin current can be pumped from one FM to the other, along the side walls of the film. On the other hand, using nanocrystalline TI films, in which the grains are large enough to avoid hybridization of the TSSs, will effectively increase the number of spin channels available for spin pumping. Here, we used an element-selective, x-ray based ferromagnetic resonance technique to demonstrate spin pumping from a FM layer at resonance through the TI layer and into the FM spin sink.</jats:p