We present the x-ray magnetic circular dichroism (XMCD) at the Ni L_2,3-edge as an evidence of the d-wave altermagnetism in rutile-structure NiF_2. Sizable XMCD signal is observed in excellent agreement with theoretical simulations. Owing to a considerable net magnetization due to spin canting, the XMCD spectrum consists of an altermagnetic signal as well as a non-negligible ferromagnetic contribution. We verify experimentally that the XMCD spectrum can be written as a sum of contributions from altermagnetism and weak ferromagnetism. Two experimental methods to isolate the ferromagnetic contribution are shown to yield essentially the same result. These are dependence of XMCD on applied magnetic fields below the Néel temperature and the XMCD measured in applied field above the Néel temperature. Our results demonstrate the utility of XMCD as a probe for altermagnetic materials with the coexisting weak ferromagnetism induced by the relativistic spin-orbit coupling.

Topological insulators become functional magnetic quantum materials once time-reversal symmetry is broken, enabling phenomena such as the quantum anomalous Hall effect and related chiral transport states. Over the past decade, we have pursued a systematic program to understand how magnetic order can be introduced, controlled, and quantitatively characterized in topological materials grown by molecular beam epitaxy. This contribution reviews our work on magnetic doping and magnetic proximity effects in (Bi,Sb)2 Te3based systems, with a particular emphasis on depth-resolved and local probes of magnetism. Using a combination of polarized neutron reflectometry, muon spin spectroscopy, and element-specific x-ray techniques, we have established where magnetic order resides, how homogeneous it is, and how it couples across interfaces. We show that magnetic doping often leads to intrinsically inhomogeneous magnetic states, while carefully engineered heterostructures can imprint or enhance magnetism in a controlled manner. Recent results on $\text{CrTe}_{2} / \text{Bi}_{2} \text{Te}_{3}$ heterostructures provide direct evidence for proximity-induced magnetism in a topological insulator without chemical doping. Together, these studies demonstrate how neutrons and muons provide essential insight into magnetic topological materials and guide the design of platforms for quantum and spintronic devices.

Antiferromagnets offer intrinsic stability against external magnetic fields, but this robustness also makes controlled manipulation of their spin structure challenging. Here we demonstrate that a thin ferromagnetic Co overlayer enables magnetic-field-induced reorientation of the Néel vector in NiO, mediated by strong interfacial coupling rather than conventional exchange bias. Using x-ray magnetic circular and linear dichroism, we show that the NiO spin structure partially aligns with the Co magnetization under applied fields, resulting in a direct correlation between ferromagnetic and antiferromagnetic domain patterns. Systematic variation of the Co thickness reveals a crossover between two distinct coupling regimes. For thin Co layers, NiO follows the Co magnetization during field cycling, whereas thicker Co layers exhibit conventional exchange bias, with NiO acting as a pinning layer. This crossover occurs at a Co thickness of approximately 3 nm, which marks the transition between inverse coupling and exchange-bias-dominated behavior.

The electron in a solid can be considered a bound state of the three independent, fundamental degrees of freedom creating quasiparticles: spinons, carrying the electron spin; plasmons, carrying the collective charge mode; and orbitons, carrying its orbital degree of freedom. These fundamental degrees of freedom could form ordering states in which dynamics or collective motions could occur and manifest as low-energy excitations. The exotic properties that appear in the materials exhibiting these electronic orderings are associated with these low-energy excitations. Although the orbital order (OO) and its coupling to the spin system creates very interesting phenomena, the microscopic origin of OO has been much less explored than other electronic properties as it is very difficult to directly access experimentally. Due to the recent improvement in energy resolution and flux, soft-x-ray resonant inelastic scattering (RIXS) allows for a reexamination of orbital excitations in manganites. Here, we present a study of low-energy excitations in half doped A -site ordered SmBaMn 2 O 6 through a combination of RIXS and soft-x-ray resonant elastic scattering measurements. We confirm the existence of OO at q = (0.25, 0.25, 0) and find various low-energy excitations below 200 meV. While several excitations can be assigned to be of magnetic and phononic origin, a group of excitations between 80 and 200 meV show a temperature dependence closely following that of the OO, making them possible candidates for orbitons.

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 (T-C) of a bilayer of (CoxFe (1-x))( 5-delta)GeTe2 (with x = 0.28) reaches similar to 300 K-a notable enhancement over most 2D ferromagnets in the ultrathin limit. Interestingly, the T(C )shows only a small dependence on film thickness (bulk T-C approximate to 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.

Synthetic antiferromagnets consist of two ferromagnetic layers that are antiferromagnetically coupled. These systems support complex dynamical magnetic excitations, where interlayer coupling gives rise to both in-phase (acoustic) and anti-phase (optical) magnonic modes. Typically, simultaneous excitation of both modes requires breaking the symmetry between the ferromagnetic layers – commonly achieved through slight misalignment of the experimental setup or by modifying the intrinsic magnetic properties. In our approach, we utilize a pinned synthetic antiferromagnet, where one of the ferromagnetic layers is exchange-coupled to an antiferromagnet. We demonstrate that by tuning the thickness of the antiferromagnet and slightly enhancing the magnetic anisotropy of the pinned layer, both acoustic and optical modes can be efficiently excited – without the need for experimental misalignment or changes to the intrinsic material properties. Under specific conditions, the magnon dispersion relations exhibit anti-crossing behavior, resulting in the emergence of a magnonic bandgap – a clear signature of strong magnon-magnon coupling. The coupling efficiency η, defined as the ratio between the bandgap and the characteristic frequency, reaches η=0.25, well in the ultrastrong and approaching the deep-strong coupling regime of η≥1. The combination of strong mode hybridization, a sizable magnonic bandgap, and high ferromagnetic resonance coherence over large areas – all achieved at room temperature without cryogenic cooling – underscores the potential of these systems for quantum magnonic applications, including quantum computing.

The effect of thermal surface cleaning on the Gilbert damping (α) of yttrium iron garnet (YIG), before capping with a metallic layer, has been investigated. Our results show that α is strongly affected by relatively mild annealing conditions (T = 300 °C) when performed in a vacuum. This increase needs to be taken into account when obtaining the spin-mixing conductance from spin pumping measurements. We measure an increase in α by a factor of ×8 when the YIG is vacuum annealed at 300 °C. No such changes in α are observed when annealed at the same temperature in 1 × 10−1 mbar of oxygen. We suggest that the main driver for the increase in α is the reduction of Fe3+ to Fe2+, as demonstrated by soft x-ray magnetic spectroscopy.

In the growing field of spintronic devices incorporating antiferromagnetic materials, control of the domain configuration and Néel axis orientation is critical for technological implementations. Here we show by X-ray magnetic linear dichroism in photoelectron emission microscopy how antiferromagnetic properties of LaFeO3 (LFO) thin films can be tailored through epitaxial strain. LFO films were grown via molecular beam epitaxy with precise stoichiometric control, using substrates that span a range of strain states—from compressive to tensile—and crystal symmetries, including different crystallographic orientations. First, we show that epitaxial strain dictates the Néel axis orientation, shifting it from completely in-plane under compressive strain to completely out-of-plane under tensile strain, regardless of the substrate crystal symmetry. Second, we find that LFO films grown on cubic substrates exhibit a fourfold distribution of antiferromagnetic domains, but can be controlled by varying the substrate miscut, while those on orthorhombic substrates, regardless of strain state, form large-scale monodomains, a highly desirable feature for spintronic applications. Precise control over antiferromagnetic domain configurations and Néel axis orientation is essential for technological advancement of spintronic devices. Here, the authors use epitaxial strain to tailor the magnetic properties of LaFeO3 thin films, demonstrating a crystal engineering approach which may have much wider applicability.

Antiferromagnets (AFs) are characterized by spin structures that are resistant to external magnetic fields, rendering them ideal for persistent information storage but challenging to control. This study demonstrates that a thin ferromagnetic adlayer can serve as a magnetic ‘lever’ to provide a strong handle on the spin texture of an adjacent antiferromagnet. In bilayers composed of NiO(001) and Co, the expected exchange bias effect—a unidirectional shift in the Co hysteresis due to coupling with NiO—is notably absent. Instead, a strong interfacial coupling is observed, causing the NiO to partially follow the magnetization of Co under an applied magnetic field. Using x-ray magnetic linear dichroism, we detect an inversion of dichroism, indicating a reorientation of the Néel vector in NiO. X-ray spectromicroscopy imaging further reveals a direct correlation between ferromagnetic and antiferromagnetic domain structures. These findings are explained using a toy model that distinguishes between stable and unstable AF domains, highlighting the dynamic interplay between NiO and the Co adlayer in the presence of a magnetic field. Published by the American Physical Society 2025

This study investigates the intrinsic magnetism and field‐driven spin alignment in NiI 2 using X‐ray absorption spectroscopy and X‐ray magnetic circular dichroism (XMCD). NiI 2 , a van der Waals material, exhibits helimagnetic and type‐II multiferroic behavior. This study reveals robust XMCD signals across paramagnetic, antiferromagnetic, and helimagnetic phases under applied out‐of‐plane fields up to 6 T, while no net moment emerges at zero field. Atomic multiplet calculations confirm a covalent Ni 3 d ground state with a significantly reduced spin moment. The results establish the intrinsic nature of NiI 2 's magnetism and clarify its field‐driven spin alignment mechanism. This comprehensive spectroscopic characterization lays the foundation for future applications of NiI 2 in advanced spintronic and multiferroic devices, despite challenges posed by its low transition temperature in the monolayer limit. Future research should focus on enhancing its critical temperature through doping, strain engineering, or heterostructure fabrication.

The search for chiral topological superconductivity in magnetic topological insulator (TI)-FeTe heterostructures is a key frontier in condensed matter physics, with potential applications in topological quantum computing. The combination of ferromagnetism, superconductivity, and topologically nontrivial surface states brings together the key elements required for chiral Majorana physics. In this work, we examine the interplay between magnetism and superconductivity at the interfaces between FeTe and a series of Te-based TI overlayers. In both Te/FeTe and superconducting MnBi2Te4/FeTe, any interfacial suppression of antiferromagnetism must affect at most a few nanometers. On the other hand, (Bi, Sb)2Te3/FeTe layers exhibit near-total suppression of antiferromagnetic ordering. Ferromagnetic Crx(Bi, Sb)2-xTe3 (CBST)/FeTe bilayers exhibit net magnetization in both CBST and FeTe layers, with evidence of interactions between superconductivity and ferromagnetism. These observations identify magnetic TI/FeTe interfaces as an exceptionally robust platform to realize chiral topological superconductivity.

Altermagnetism is a recently identified magnetic symmetry class combining characteristics of conventional collinear ferromagnets and antiferromagnets, that were regarded as mutually exclusive, and enabling phenomena and functionalities unparalleled in either of the two traditional elementary magnetic classes. In this work we use symmetry, ab initio theory, and experiments to explore x-ray magnetic circular dichroism (XMCD) in the altermagnetic class. As a representative material for our XMCD study we choose α-MnTe with compensated antiparallel magnetic order in which an anomalous Hall effect has been already demonstrated. We predict and experimentally confirm a characteristic XMCD line shape for compensated moments lying in a plane perpendicular to the light propagation vector. Our results highlight the distinct phenomenology in altermagnets of this time-reversal symmetry breaking response, and its potential utility for element-specific spectroscopy and microscopy.

The van der Waals interaction enables atomically thin layers of exfoliated 2D materials to be interfaced in heterostructures with relaxed epitaxy conditions, however, the ability to exfoliate and freely stack layers without any strain or structural modification is by no means ubiquitous. In this work, the piezoelectricity of the exfoliated van der Waals piezoelectric alpha-In2Se3 is utilized to modify the magnetic properties of exfoliated Fe3GeTe2, a van der Waals ferromagnet, resulting in increased domain wall density, reductions in the transition temperature ranging from 5 to 20 K, and an increase in the magnetic coercivity. Structural modifications at the atomic level are corroborated by a comparison to a graphite/alpha-In2Se3 heterostructure, for which a decrease in the Tuinstra-Koenig ratio is found. Magnetostrictive ferromagnetic domains are also observed, which may contribute to the enhanced magnetic coercivity. Density functional theory calculations and atomistic spin dynamic simulations show that the Fe3GeTe2 layer is compressively strained by 0.4%, reducing the exchange stiffness and magnetic anisotropy. The incorporation of alpha-In2Se3 may be a general strategy to electrostatically strain interfaces within the paradigm of hexagonal boron nitride-encapsulated heterostructures, for which the atomic flatness is both an intrinsic property and paramount requirement for 2D van der Waals heterojunctions. This study focuses on the captivating interplay between the ferromagnetic Fe3GeTe2 and the piezoelectric alpha-In2Se3, both 2D van der Waals (vdW) materials. Strained heterojunctions exhibit several compelling transformations: increased domain density, reduced Curie temperature, and emergent magnetostrictive ferromagnetic domains. Using alpha-In2Se3 is a versatile approach to strain-tune vdW materials, including graphite and Te based vdW chalcogenides. image

We present a spectroscopic study of the magnetic properties ofFe3-δGeTe2single crystals with varying Fe content, achieved by tuning the stoichiometry of the crystals. We carried out x-ray absorption spectroscopy and analyzed the x-ray circular magnetic dichroism spectra using the sum rules, to determine the orbital and spin magnetic moments of the materials. We find a clear reduction of the spin and orbital magnetic moment with increasing Fe deficiency. Magnetic susceptibility measurements show that the reduction in magnetization is accompanied by a reduced Curie temperature. Multiplet calculations reveal that the Fe2+state increasingly mixes with a higher valence state when the Fe deficiency is increased. This effect is correlated with the weakening of the magnetic moment. As single crystals are the base material for exfoliation processes, our results are relevant for the assembly of 2D magnetic heterostructures.

In-materia reservoir computing (RC) leverages the intrinsic physical responses of functional materials to perform complex computational tasks. Magnetic metamaterials are exciting candidates for RC due to their huge state space, nonlinear emergent dynamics, and non-volatile memory. However, to be suitable for a broad range of tasks, the material system is required to exhibit a broad range of properties, and isolating these behaviours experimentally can often prove difficult. By using an electrically accessible device consisting of an array of interconnected magnetic nanorings- a system shown to exhibit complex emergent dynamics- here we show how reconfiguring the reservoir architecture allows exploitation of different aspects the system’s dynamical behaviours. This is evidenced through state-of-the-art performance in diverse benchmark tasks with very different computational requirements, highlighting the additional computational configurability that can be obtained by altering the input/output architecture around the material system.

Pointed magnetic elements are introduced as an improvement upon rectangular strips currently employed in composite element magnetic barcodes. The coercivity of these elements, as measured using the magneto-optic Kerr effect, is found to strictly adhere to a single power law relationship with the element width, where the power law exponent is dependent on the length of the pointed region and takes values between −0.98 and −0.91. The steeper gradients here, along with the absence of the crossover region seen in rectangular devices, present these structures as a strict improvement in terms of potential device applications. These improvements are found to be present for all structures where the pointed region is as long as, or longer than, the magnetic element is wide. The remanent magnetization configuration, imaged using photo-emission microscopy with contrast from x-ray magnetic circular dichroism (XMCD-PEEM), is compared to the results of micromagnetic simulations. It is found to cant inward in the pointed section of the strip, aligning with the edges of the point, pinning the magnetization and giving a consistent magnetization reversal behavior for all element widths investigated.

In the version of this article initially published, the y-axis range of the violin plots in Fig. 4a, now spanning between 0.0 and 1.0, spanned between 0.2 and 1.0.Furthermore, in the leftmost panel, titled "Coupled Map Lattice (CML)," the labels and colours for the five distributions of the dynamical regimes of the coupled map lattices were misplaced, which caused them to appear shuffled and not in agreement with the main text and results from Fig. 3a.

To harness the intriguing properties of 2D van der Waals (vdW) ferromagnets (FMs) for versatile applications, the key challenge lies in the reliable material synthesis for scalable device production. Here, the epitaxial growth of single‐crystalline 1 T ‐CrTe 2 thin films on 2‐inch sapphire substrates are demonstrated. Benefiting from the uniform surface energy of the dangling bond‐free Al 2 O 3 (0001) surface, the layer‐by‐layer vdW growth mode is observed right from the initial growth stage, which warrants precise control of the sample thickness beyond three monolayer and homogeneous surface morphology across the entire wafer. Moreover, the presence of the Coulomb interaction at the CrTe 2 /Al 2 O 3 interface plays an important role in tailoring the anomalous Hall response, and the structural optimization of the CrTe 2 ‐based spin‐orbit torque device leads to a substantial switching power reduction by 54%. The results may lay out a general framework for the design of energy‐efficient spintronics based on configurable vdW FMs.

The understanding of antiferromagnetic domain walls, which are the interface between domains with different Neel order orientations, is a crucial aspect to enable the use of antiferromagnetic materials as active elements in future spintronic devices. In this work, we demonstrate that in antiferromagnetic NiO/Pt bilayers arbitraryshaped structures can be generated by switching driven by electrical current pulses. The generated domains are T domains, separated from each other by a domain wall whose spins are pointing toward the average direction of the two T domains rather than the common axis of the two planes. Interestingly, this direction is the same for the whole domain wall indicating the absence of strong Lifshitz invariants. The domain wall can be micromagnetically modeled by strain distributions in the NiO thin film induced by the MgO substrate, deviating from the bulk anisotropy. From our measurements we determine the domain-wall width to have a full width at half maximum of A = 98 +/- 10 nm, demonstrating strong confinement.