Exciton dynamics in layered magnetic semiconductors provide a sensitive probe of the interplay between spin order and light-matter interaction. Here, we study thin CrSBr layers using time-resolved photoluminescence spectroscopy in an external magnetic field, revealing a step-like reduction in the exciton lifetime from 11 to 7 ps, during the magnetization flip from the antiferromagnetic to the ferromagnetic phase. The reduction of the exciton lifetime in the ferromagnetic phase persists below the Néel temperature, as evidenced by its strong magnetic-field dependence that disappears in the paramagnetic phase. Ab initio calculations reveal a one-dimensional nature of free excitons accompanied by a pronounced change in the oscillator strength across the magnetic phase transition predicting a shorter radiative lifetime of free excitons in the antiferromagnetic phase of CrSBr contradicting the experimental observations. This discrepancy is explained by strong localization of excitons at low tempature. We show both experimentally and theoretically that the observed magnetic switching of the exciton lifetime is attributed to a larger exciton localization volume leading to a larger oscillator strength in the ferromagnetic phase. The results show that disorder-induced localization effects play a key role in exciton dynamics in CrSBr.

The discovery of chiral helical magnetism (CHM) in Cr1/3NbS2 and the stabilization of a chiral soliton lattice has attracted considerable interest in view of their potential technological applications. However, there is an ongoing debate regarding whether the sister compound, Mn1/3NbS2, which shares the same crystal structure, exhibits similar nontrivial properties which likewise rely on the lack of inversion symmetry at the magnetic ion. In this study, we conduct a comprehensive investigation of the magnetically ordered states of both compounds, using Cr-53, Mn-55, and Nb-93 NMR. Our results, supported by density-functional calculations, detect in a highquality single crystal of Cr1/3NbS2 all the signatures of the monoaxial CHM in a magnetic field, identifying it as a reference case for NMR. The detailed understanding of this prototypic behavior provides a reference for Mn1/3NbS2. Despite the much larger density of specific defects in this second material, we confirm the presence of a CHM phase in the Mn compound, characterized by a very large critical field for the forced ferromagnetic phase (approximate to 5 T for the applied field along c).

We report a systematic study of the structural and magnetic evolution in CeAlSi1-xGex, a series of materials which provide a tunable platform for exploring magnetism in noncentrosymmetric Ce-based intermetallics. Polycrystalline samples and single crystals were synthesized using arc melting and flux growth techniques. Structural characterization by X-ray diffraction shows a continuous increase in the unit-cell parameters with increasing Ge content, with no evidence of a structural phase transition across the series. Magnetization measurements reveal a suppression of the ferromagnetic ordering temperature of CeAlSi with increasing Ge substitution, indicating a crossover toward anti-ferromagnetic behaviour in Ge-rich compositions. Neutron diffraction measurements performed on selected compositions show that weak magnetic intensity appears on some structural Bragg peaks below the magnetic ordering temperature. These results elucidate the relationship between chemical substitution, crystal structure, and magnetic ground states in CeAlSi1-xGex, and establish this system as a model platform for studying compositionally tuned magnetic order in noncentrosymmetric materials.

We report a systematic study of the structural and magnetic evolution in CeAlSi 1– x Ge x , a series of materials which provide a tunable platform for exploring magnetism in noncentrosymmetric Ce-based intermetallics. Polycrystalline samples and single crystals were synthesized using arc melting and flux growth techniques. Structural characterization by X-ray diffraction shows a continuous increase in the unit-cell parameters with increasing Ge content, with no evidence of a structural phase transition across the series. Magnetization measurements reveal a suppression of the ferromagnetic ordering temperature of CeAlSi with increasing Ge substitution, indicating a crossover toward antiferromagnetic behaviour in Ge-rich compositions. Neutron diffraction measurements performed on selected compositions show that weak magnetic intensity appears on some structural Bragg peaks below the magnetic ordering temperature. These results elucidate the relationship between chemical substitution, crystal structure, and magnetic ground states in CeAlSi 1– x Ge x , and establish this system as a model platform for studying compositionally tuned magnetic order in noncentrosymmetric materials.

Altermagnets host non-relativistic spin-split electronic states whose microscopic origin is theoretically linked to a hidden charge order, yet experimental studies of this charge order are limited. We therefore investigate charge order within CoF_2, a d-wave altermagnetic compound with a rutile crystal structure and Γ-point antiferromagnetism. Combining resonant elastic X-ray scattering, symmetry analysis and ab initio calculations, we directly observe charge ordering and identify it as antiferroquadrupolar in nature. Via electronic structure calculations, we show that the experimentally observed antiferroquadrupolar order gives rise to the characteristic altermagnetic spin-splitting, thereby establishing empirical evidence for the decomposition of the altermagnetic order parameter into magnetic and charge degrees of freedom. We hence demonstrate that antiferroquadrupolar order is the microscopic origin of altermagnetism in CoF_2, with implications to the wider family of rutile altermagnets. Furthermore, our approach is applicable to studying altermagnetism in general, having demonstrated that resonant elastic X-ray scattering can serve as a direct probe of the charge multipoles that underpin spin-split electronic states in these materials.

The magnetic phase diagram, magnetoelastic coupling, and uniaxial pressure effects of centrosymmetric magnetic skyrmion-hosting GdRu2Si2 are investigated by means of high-resolution capacitance dilatometry in fields up to 15 T supported by specific-heat and magnetization studies. In addition to the previously reported phases in the H-T phase diagram, we observe a third antiferromagnetic phase in zero magnetic field. We present the magnetic phase diagram and find two unreported phases, one of which features a comparably giant uniaxial pressure dependence. Our dilatometric measurements show magnetoelastic effects associated with the various magnetic ordering phenomena. We determine the uniaxial pressure dependencies of the various phases, in particular of the skyrmion lattice phase which is enhanced at higher fields and temperatures and also widens at a rate of 0.07 T/GPa when uniaxial pressure is applied along the c axis. The relevance of fluctuations is further highlighted by the presence of a tricritical point indicated by our thermodynamic data at the phase boundary separating two double-Q magnetic configurations between which the skyrmion pocket phase evolves upon further cooling.

Centrosymmetric GdRu2Si2 exhibits a variety of multi-Q magnetic states as a function of temperature and applied magnetic field, including a square skyrmion-lattice phase. The material's behavior is strongly dependent on the direction of the applied field, with different phase diagrams resulting for fields applied parallel or perpendicular to the crystallographic c axis. Here, we present the results of muon-spin relaxation (μ+SR) measurements on single crystals of GdRu2Si2. Our analysis is based on the computation of muon stopping sites and consideration of quantum zero-point motion effects of muons, allowing direct comparison with the underlying spin textures in the material. The muon site is confirmed experimentally, using angle-dependent measurements of the muon Knight shift. Using transverse-field μ+SR with fields applied along either the [001] or [100] crystallographic directions, we distinguish between the magnetic phases in this system via their distinct muon response, providing additional evidence for the skyrmion and meron-lattice phases, while also suggesting the existence of RKKY-driven muon hyperfine coupling. Zero-field μ+SR provides clear evidence for a transition between two distinct magnetically ordered phases at 39 K. Published by the American Physical Society 2025

The intertwined nature of magnetic and electric degrees of freedom in magnetoelectric (ME) materials is well described by ME-coupling theory. When an external electric field is applied to a ME material, the ME coupling induces unique and intriguing magnetic responses. Such responses underpin the utilisation of ME materials across diverse applications, ranging from electromagnetic sensing to low-energy digital memory technologies. Here, we use small angle neutron scattering and discover a novel magnetic response within an archetypal chiral ME material, Cu2OSeO3. We find that the propagation direction of an incommensurate magnetic spiral is deterministically actuated and deflected along controllable trajectories. Furthermore, we predict the emergence of distinct non-linear regimes of spiral-deflection behaviour with external electric and magnetic fields, unlocking innovative devices that leverage controlled and customisable variations in macroscopic polarisation and magnetisation.

Skyrmions are particlelike vortices of magnetization with nontrivial topology, which are usually stabilized by Dzyaloshinskii-Moriya interactions (DMI) in noncentrosymmetric bulk materials. Exceptions are centrosymmetric Gd- and Eu-based skyrmion-lattice (SL) hosts with zero DMI, where both the SL stabilization mechanisms and magnetic ground states remain controversial. We address these here by investigating both the static and dynamical spin properties of the centrosymmetric SL host Gd2PdSi3 using muon spectroscopy. We find that spin fluctuations in the noncoplanar SL phase are highly anisotropic, implying that spin anisotropy plays a prominent role in stabilizing this phase. We also observe strongly anisotropic spin dynamics in the ground-state (IC-1) incommensurate magnetic phase of the material, indicating that it hosts a meronlike multi-q structure. In contrast, the higher-field, coplanar IC-2 phase is found to be single q with nearly isotropic spin dynamics.

We present the results of muon-spin relaxation (μ+SR) measurements of the van der Waals magnet NiI2, which probe magnetic phase transitions at TN1=73K and TN2=62K. Supporting density functional theory (DFT) calculations allow the determination of a single muon stopping site whose magnetic environment is consistent with the proposed ground-state magnetic structure. μ+SR measurements of the dynamics reveal behavior consistent with spin-wave excitations below TN2. In the region TN2

Understanding the formation of skyrmions in centrosymmetric materials is a problem of fundamental and technological interest. GdRu2Si2 is a candidate material that hosts a variety of multi-Q magnetic phases, including in zero-field. Here, inelastic neutron scattering is used to measure the spin excitations in the field-polarized phase of GdRu2Si2. Linear spin wave theory and a method of interaction invariant path analysis are used to derive a Hamiltonian accounting for the spectra. The Hamiltonian, dominated by bilinear (Ruderman-Kittel-Kasuya-Yosida) Heisenberg exchange, compares favorably to ab initio calculations. Dipolar interactions are a secondary energy scale to consider, with JD.D~ 0.05JRKKY. However, it is shown that in the field-polarized phase the dipolar interactions ‘self screen’ so that their effect is largely suppressed. No specific evidence for higher-order exchange is found. These aspects are discussed in the context of the lower field multi-Q states and the anisotropy of the system.

We present an extensive X-ray and neutron scattering study of the structure and magnetic excitations of Nd_2PdSi_3, a sister compound of Gd_2PdSi_3 which was recently found to host a skyrmion lattice phase despite its centrosymmetric crystal structure. Dispersive magnetic excitations were measured throughout the Brillouin zone and modeled to determine the magnetic interactions between Nd ions. Our analysis reveals that the magnetic interactions in this system extend over large distances and are significantly affected by a crystallographic superstructure formed by ordering of the Pd and Si atoms. The results suggest that the mechanism for the skyrmion phase formation in this family of materials, specifically Gd_2PdSi_3, is through the long-range RKKY interactions rather than short-range triangular-lattice frustration.

We report on the properties of SrTb2O4, a frustrated zigzag ladder antiferromagnet, studied by single crystal neutron diffraction (with polarised neutrons in zero field and unpolarised neutrons in an applied magnetic field), as well as by neutron spectroscopy on a polycrystalline sample. The neutron scattering results are supported by single crystal magnetisation and heat capacity measurements. In zero field, neutron diffraction data show no transition to a magnetically ordered state down to the lowest experimentally available temperature of 35 mK, and the material remains magnetically disordered down to this temperature. Polarised neutron diffraction measurements reveal the presence of a diffuse scattering signal suggesting only very weak spin-spin correlations in the ground state. For H // c (the easy magnetisation direction), we followed the magnetisation process using neutron diffraction measurements and observed the appearance of field-induced magnetic Bragg peaks with integer h and k indices in the (hk0) scattering plane. No magnetic peaks with a non-zero propagation vector were detected. The observed in-field data fit well to a simple two-sublattice model with magnetic moments aligned along the field direction but being significantly different in magnitude for the two inequivalent Tb3+ sites in the unit cell. Overall, the collected data point to a nonmagnetic ground state in SrTb2O4 despite the presence of strong interactions.

InBi is a semimetal with topologically non-trivial electronic surface states, which is also chemically and structurally compatible with conventional III-V semiconductors. Single crystal InBi has been grown and its (001) cleave surfaces studied. They do not conform to the single Bi-Bi cleave plane previously assumed in band structure studies of the material but instead expose both In- and Bi-terminated surface regions. Crystals cleaved in ultra-high vacuum have been used as substrates for ultra-low temperature homoepitaxy via periodic supply epitaxy (PSE) with alternate Bi and In fluxes. Homoepitaxial growth of good quality InBi was not achieved under these conditions. The 3D and 2D surface structures produced by PSE were studied by reflection high energy electron diffraction and atomic force microscopy. By studying InBi homoepitaxy for the first time, this work highlights the challenge of growing high quality InBi epilayers beyond the ultra-thin heteroepitaxial layers recently demonstrated [Molecules 2024, 29(12), 2825].

The Eu(Ga1−xAlx)4 series is composed of centrosymmetric structures which exhibit a wide range of rich topological phenomena, including some members hosting magnetic skyrmions. In this letter, we investigate the previously unreported intermediate compound EuGa2.4Al1.6, which hosts two distinct phase transitions under zero applied magnetic field. We have used resonant elastic x-ray scattering with full linear polarization analysis to unambiguously determine the zero-field magnetic structures, which consist of a transition between a basal plane transverse spin density wave at higher temperatures into a noncollinear helical ground state. Furthermore, we demonstrate a phase coexistence regime below the transition and reveal an elliptically modulated helical magnetic structure emerging from wavevector splitting. Published by the American Physical Society 2024

The rare-earth palladium silicides host an array of complex magnetic phases. In this paper, we report the growth of large single crystals of the R2PdSi3 family, (where R= Ce, Nd, Gd, Tb, Ho and Er) by the floating zone technique using a high-power xenon arc-lamp furnace. The crystal boules obtained have been examined for their quality using x-ray diffraction techniques, elemental analysis, and their magnetic properties have been investigated through temperature dependent magnetisation measurements.

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

Two-dimensional (2D) van der Waals (vdW) magnets have recently emerged as novel skyrmion hosts. This discovery has opened a new material platform for tuning the properties of topological spin textures, such as by exploiting proximity effects induced by stacking of 2D materials into heterostructures, or by directly manipulating the structural composition of the host material. Previous works have considered the effect of varied composition in the bulk crystals of the vdW magnet Fe3-xGeTe2 , but so far the effects on the hosted spin textures have not been thoroughly investigated. In this work, real-space x-ray microscopy is utilized to image magnetic stripe domain, skyrmion and composite skyrmion states in exfoliated flakes of Fe3-xGeTe2 with varying Fe deficiency x. In combination with supporting mean-field and micromagnetic simulations, the significant alterations in the magnetic phase diagrams of the flakes, and thus the stability of the observed spin textures, are revealed. These arise as a result of the varying temperature dependence of the fundamental magnetic properties, which are greater than can be explained by the removal of spins, and are consistent with previously reported changes in the electronic band structure via the Fe deficiency.