Spin disorder control of topological spin texture.

Stabilization of topological spin textures in layered magnets has the potential to drive the development of advanced low-dimensional spintronics devices. However, achieving reliable and flexible manipulation of the topological spin textures beyond skyrmion in a two-dimensional magnet system remains challenging. Here, we demonstrate the introduction of magnetic iron atoms between the van der Waals gap of a layered magnet, FeGaTe, to modify local anisotropic magnetic interactions.

Reversible non-volatile electronic switching in a near-room-temperature van der Waals ferromagnet.

Non-volatile phase-change memory devices utilize local heating to toggle between crystalline and amorphous states with distinct electrical properties. Expanding on this kind of switching to two topologically distinct phases requires controlled non-volatile switching between two crystalline phases with distinct symmetries. Here, we report the observation of reversible and non-volatile switching between two stable and closely related crystal structures, with remarkably distinct electronic structures, in the near-room-temperature van der Waals ferromagnet FeGeTe.

Room-Temperature, Current-Induced Magnetization Self-Switching in A Van Der Waals Ferromagnet.

2D layered materials with broken inversion symmetry are being extensively pursued as  spin source layers to realize high-efficiency magnetic switching. Such low-symmetry layered systems are, however, scarce. In addition, most layered magnets with perpendicular magnetic anisotropy show a low Curie temperature.

Discovery of Charge Order in the Transition Metal Dichalcogenide Fe_{x}NbS_{2}.

The Fe intercalated transition metal dichalcogenide (TMD), Fe_{1/3}NbS_{2}, exhibits remarkable resistance switching properties and highly tunable spin ordering phases due to magnetic defects. We conduct synchrotron x-ray scattering measurements on both underintercalated (x=0.32) and overintercalated (x=0.

Long-range, non-local switching of spin textures in a frustrated antiferromagnet.

Antiferromagnetic spintronics is an emerging area of quantum technologies that leverage the coupling between spin and orbital degrees of freedom in exotic materials. Spin-orbit interactions allow spin or angular momentum to be injected via electrical stimuli to manipulate the spin texture of a material, enabling the storage of information and energy. In general, the physical process is intrinsically local: spin is carried by an electrical current, imparted into the magnetic system, and the spin texture will then rotate in the region of current flow.

Ordering of room-temperature magnetic skyrmions in a polar van der Waals magnet.

Control and understanding of ensembles of skyrmions is important for realization of future technologies. In particular, the order-disorder transition associated with the 2D lattice of magnetic skyrmions can have significant implications for transport and other dynamic functionalities. To date, skyrmion ensembles have been primarily studied in bulk crystals, or as isolated skyrmions in thin film devices.

Discovery of charge density wave in a kagome lattice antiferromagnet.

A hallmark of strongly correlated quantum materials is the rich phase diagram resulting from competing and intertwined phases with nearly degenerate ground-state energies. A well-known example is the copper oxides, in which a charge density wave (CDW) is ordered well above and strongly coupled to the magnetic order to form spin-charge-separated stripes that compete with superconductivity. Recently, such rich phase diagrams have also been shown in correlated topological materials.

Pervasive beyond Room-Temperature Ferromagnetism in a Doped van der Waals Magnet.

The existence of long-range magnetic order in low-dimensional magnetic systems, such as the quasi-two-dimensional van der Waals (vdW) magnets, has attracted intensive studies of new physical phenomena. The vdW Fe_{N}GeTe_{2} (N=3, 4, 5; FGT) family is exceptional, owing to its vast tunability of magnetic properties. In particular, a ferromagnetic ordering temperature (T_{C}) above room temperature at N=5 (F5GT) is observed.

Room-temperature skyrmion lattice in a layered magnet (FeCo)GeTe.

Novel magnetic ground states have been stabilized in two-dimensional (2D) magnets such as skyrmions, with the potential next-generation information technology. Here, we report the experimental observation of a Néel-type skyrmion lattice at room temperature in a single-phase, layered 2D magnet, specifically a 50% Co-doped FeGeTe (FCGT) system. The thickness-dependent magnetic domain size follows Kittel's law.

Gate-Tunable Transport in Quasi-One-Dimensional α-BiI Field Effect Transistors.

BiI belongs to a novel family of quasi-one-dimensional (1D) topological insulators (TIs). While its β phase was demonstrated to be a prototypical weak TI, the α phase, long thought to be a trivial insulator, was recently predicted to be a rare higher order TI. Here, we report the first gate tunable transport together with evidence for unconventional band topology in exfoliated α-BiI field effect transistors.

Tunable room-temperature ferromagnetism in Co-doped two-dimensional van der Waals ZnO.

The recent discovery of ferromagnetism in two-dimensional van der Waals crystals has provoked a surge of interest in the exploration of fundamental spin interaction in reduced dimensions. However, existing material candidates have several limitations, notably lacking intrinsic room-temperature ferromagnetic order and air stability. Here, motivated by the anomalously high Curie temperature observed in bulk diluted magnetic oxides, we demonstrate room-temperature ferromagnetism in Co-doped graphene-like Zinc Oxide, a chemically stable layered material in air, down to single atom thickness.

Structural, magnetic, and electronic evolution of the spin-ladder system BaFeS Se with isoelectronic substitution.

We report experimental studies of a series of BaFeS Se (0 ⩽ ⩽ 3) single crystals and powder specimens using x-ray diffraction, neutron-diffraction, muon-spin-relaxation, and electrical transport measurements. A structural transformation from (BaFeS) to (BaFeSe) was identified around = 0.7 - 1.

Short-Range Nematic Fluctuations in Sr_{1-x}Na_{x}Fe_{2}As_{2} Superconductors.

Interactions between nematic fluctuations, magnetic order and superconductivity are central to the physics of iron-based superconductors. Here we report on in-plane transverse acoustic phonons in hole-doped Sr_{1-x}Na_{x}Fe_{2}As_{2} measured via inelastic x-ray scattering, and extract both the nematic susceptibility and the nematic correlation length. By a self-contained method of analysis, for the underdoped (x=0.

In-plane uniaxial pressure-induced out-of-plane antiferromagnetic moment and critical fluctuations in BaFeAs.

A small in-plane external uniaxial pressure has been widely used as an effective method to acquire single domain iron pnictide BaFeAs, which exhibits twin-domains without uniaxial strain below the tetragonal-to-orthorhombic structural (nematic) transition temperature T. Although it is generally assumed that such a pressure will not affect the intrinsic electronic/magnetic properties of the system, it is known to enhance the antiferromagnetic (AF) ordering temperature T ( < T) and create in-plane resistivity anisotropy above T. Here we use neutron polarization analysis to show that such a strain on BaFeAs also induces a static or quasi-static out-of-plane (c-axis) AF order and its associated critical spin fluctuations near T/T.

Strain-Induced Spin-Nematic State and Nematic Susceptibility Arising from 2×2 Fe Clusters in KFe_{0.8}Ag_{1.2}Te_{2}.

Spin nematics break spin-rotational symmetry while maintaining time-reversal symmetry, analogous to liquid crystal nematics that break spatial rotational symmetry while maintaining translational symmetry. Although several candidate spin nematics have been proposed, the identification and characterization of such a state remain challenging because the spin-nematic order parameter does not couple directly to experimental probes. KFe_{0.

Observation of a -type short-range antiferromagnetic order in layer spacing expanded FeS.

We report neutron diffraction studies of FeS single crystals obtained from Rb Fe S single crystals via a hydrothermal method. While no iron vacancy order or block antiferromagnetic order typical of Rb Fe S is found in our samples, we observe -type short-range antiferromagnetic order with moments pointed along the axis hosted by a different phase of FeS with an expanded interlayer spacing. The Néel temperature for this magnetic order is determined to be 170 ± 4 K.

Charge ordering in superconducting copper oxides.

Charge order has recently been identified as a leading competitor of high-temperature superconductivity in moderately doped cuprates. We provide a survey of universal and materials-specific aspects of this phenomenon, with emphasis on results obtained by scattering methods. In particular, we discuss the structure, periodicity, and stability range of the charge-ordered state, its response to various external perturbations, the influence of disorder, the coexistence and competition with superconductivity, as well as collective charge dynamics.

Intertwined Magnetic and Nematic Orders in Semiconducting KFe_{0.8}Ag_{1.2}Te_{2}.

Superconductivity in the iron pnictides emerges from metallic parent compounds exhibiting intertwined stripe-type magnetic order and nematic order, with itinerant electrons suggested to be essential for both. Here we use x-ray and neutron scattering to show that a similar intertwined state is realized in semiconducting KFe_{0.8}Ag_{1.

Gradual enhancement of stripe-type antiferromagnetism in the spin-ladder material BaFeS under pressure.

We report pressure-dependent neutron diffraction and muon spin relaxation/rotation measurements combined with first-principles calculations to investigate the structural, magnetic, and electronic properties of BaFeS under pressure. The experimental results reveal a gradual enhancement of the stripe-type ordering temperature with increasing pressure up to 2.6 GPa and no observable change in the size of the ordered moment.

Local Orthorhombicity in the Magnetic C_{4} Phase of the Hole-Doped Iron-Arsenide Superconductor Sr_{1-x}Na_{x}Fe_{2}As_{2}.

We report on temperature-dependent pair distribution function measurements of Sr_{1-x}Na_{x}Fe_{2}As_{2}, an iron-based superconductor system that contains a magnetic phase with reentrant tetragonal symmetry, known as the magnetic C_{4} phase. Quantitative refinements indicate that the instantaneous local structure in the C_{4} phase comprises fluctuating orthorhombic regions with a length scale of ∼2  nm, despite the tetragonal symmetry of the average static structure. Additionally, local orthorhombic fluctuations exist on a similar length scale at temperatures well into the paramagnetic tetragonal phase.

Spin-polarized surface resonances accompanying topological surface state formation.

Topological insulators host spin-polarized surface states born out of the energetic inversion of bulk bands driven by the spin-orbit interaction. Here we discover previously unidentified consequences of band-inversion on the surface electronic structure of the topological insulator BiSe. By performing simultaneous spin, time, and angle-resolved photoemission spectroscopy, we map the spin-polarized unoccupied electronic structure and identify a surface resonance which is distinct from the topological surface state, yet shares a similar spin-orbital texture with opposite orientation.

Atomic-scale control of magnetic anisotropy via novel spin-orbit coupling effect in La2/3Sr1/3MnO3/SrIrO3 superlattices.

Magnetic anisotropy (MA) is one of the most important material properties for modern spintronic devices. Conventional manipulation of the intrinsic MA, i.e.