Abstract Cobalt-doped Fe _5 GeTe _2 possesses a rich magnetic phase diagram as a function of Co concentration. The nature of magnetic order in (Co _{0 .5} Fe _{0 .5} ) _5 GeTe _2 is especially interesting, as it has been shown to exhibit ferromagnetic order, A-type antiferromagnetic (AFM) order, or potentially both at the same time. Here we present magnetoresistance measurements on AFM (Co _{0 .5} Fe _{0 .5} ) _5 GeTe _5 at a series of pressures and extract the anisotropy and interlayer exchange fields using the two-sublattice model. We show a 50% increase of the interlayer exchange at 2 GPa, highlighting the sensitivity of magnetic properties to interlayer distance. In addition, we find that the sharp hysteretic transitions observed within the AFM state can be qualitatively described by a linear chain model, which suggests an even–odd effect as a function of layer number instead of a coexisting ferromagnetic phase.

We present a comprehensive analysis of magnetotransport across monolayer 1T'-WTe2, highlighting the role of nonsymmorphic symmetries in governing edge-state spin behavior. By comparing the electronic transmission in nanoribbons with edges along the crystallographic y and x directions, our analysis reveals a pronounced anisotropy in the magnetic-field response. The y-edge ribbon exhibits significant spin splitting of the edge-state bands in both energy and momentum space, together with a strong angular dependence of the conductance. The observed magnetotransport response indicates a spin quantization axis that aligns with the out-of-plane spin quantization axis reported in previous experimental studies. In contrast, the x-edge ribbon shows negligible spin splitting with magnetic fields, which is attributed to nonsymmorphic symmetries such as glide mirror and screw rotation, which protects degeneracies along the P-X direction, even when time-reversal symmetry is broken. The energy-resolved current density and angular transmission analysis confirm that this anisotropy originates from edge states, while bulk states remain largely insensitive to the field orientation. Our results establish direct transport spectroscopy based evidence of nonsymmorphic symmetry-protected spin degeneracy in 1T'-WTe2, and underscore its promise for spintronic devices that leverage symmetry-protected and directionally selective transport channels.

Two-dimensional (2D) semiconductors have emerged as exciting candidates for the development of low-power and multifunctional computing applications, thanks to their qualities such as layer-dependent band gap tunability, high carrier mobility, and excellent electrostatic control. Here, we explore a pair of 2D semiconductors with nearly broken-gap (Type-III-like) band alignment and demonstrate a highly gate-tunable p-MoTe2/n-SnS2 heterojunction with multifunctional behavior. Employing a dual-gated asymmetric device geometry, we unveil its functionality as both a forward and backward rectifying device. Moreover, we observe a highly gate-tunable negative differential resistance (NDR), with a gate-coupling efficiency of η ≃ 0.5 and a peak-to-valley ratio of ∼ 3 down to 150 K. By employing density functional theory, we determine that the observed NDR is dominated by valence band-to-valence band tunneling, while additional interband tunneling contributions arise at higher bias. The combination of tunneling driven transport and gate controllability of NDR opens the pathway for realizing gate-tunable 2D material-based neuromorphic and energy-efficient electronics.

Cobalt-doped Fe_5GeTe_2 possesses a rich magnetic phase diagram as a function of Co concentration. The nature of magnetic order in (Co_0.5Fe_0.5)_5GeTe_2 is especially interesting, as it has been shown to exhibit ferromagnetic order, A-type antiferromagnetic (AFM) order, or potentially both at the same time. Here we present magnetoresistance measurements on antiferromagnetic (Co_0.5Fe_0.5)_5GeTe_2 at a series of pressures and extract the anisotropy and interlayer exchange fields using the two-sublattice model. We show a 50

While the growing utilization of polymers in flexible electronic devices has sparked significant interest in polymer/metal interfaces, spintronic studies of such interfaces remain limited. Here, spin pumping across a polymer/ferromagnet metal interface is systematically studied between hydrogen silsesquioxane (HSQ) oligomer layers (t HSQ = 30, 36, 48 nm) and NiFe (t NiFe = 4, 5, 7, 10 nm) thin films. Using ferromagnetic resonance measurements, strong spin pumping (large linewidth broadening) and a giant spin mixing conductance, reaching 19.8 nm −2 for HSQ = 48 nm are observed, i.e. comparable to that of heavy metals. The results suggest efficient spin transfer across the HSQ/NiFe interface, possibly originating from a combination of spin and orbital pumping, and provide valuable insights for designing self‐powered and flexible spintronic devices utilizing polymers in combination with ferromagnetic materials.

Spin Hall nano-oscillators (SHNOs) are emerging spintronic oscillators with significant potential for technological applications, including microwave signal generation, and unconventional computing. Despite their promising applications, SHNOs face various challenges, such as high energy consumption and difficulties in growing high-quality thin film heterostructures with clean interfaces. Here, single-layer topological magnetic Weyl semimetals open a possible solution as they possess both intrinsic ferromagnetism and a large spin-orbit coupling due to their topological properties. However, producing such high-quality thin films of magnetic Weyl semimetals that retain their topological properties and Berry curvature remains a challenge. We address these issues with high-quality single-layer epitaxial ferromagnetic Co2MnGa Weyl semimetal thin film-based SHNOs. We observe a giant spin Hall conductivity, σSHC = (6.08 ± 0.02) × 105 (ℏ/2e) Ω-1 m-1, which is an order of magnitude higher than previous reports. Theoretical calculations corroborate the experimental results with a large intrinsic spin Hall conductivity due to presence of a strong Berry curvature. Further, self spin-orbit torque driven magnetization auto-oscillations are demonstrated for the first time, at an ultralow threshold current density of Jth = 6.2 × 1011 A m-2. These findings indicate that magnetic Weyl semimetals have tremendous application potential for developing energy-efficient spintronic devices.

Altermagnets are a new class of magnetic materials characterized by fully compensated spins arranged in alternating local structures, allowing for spin-split bands similar to those found in ferromagnets without net magnetism. Recently, MnTe has emerged as a prototypical altermagnetic material exhibiting spin-polarized electronic bands and anomalous transport phenomena. Although recent work has explored the magnetic and structural properties of MnTe, detailed experimental investigations into the relationship between altermagnetic order and crystal symmetry are lacking. Here, we report the relationship between altermagnetic order and crystal symmetry by investigating magnetotransport properties of MnTe epitaxial altermagnetic thin films grown by molecular beam epitaxy. We observe a spontaneous anomalous Hall effect and show the control of Hall response with the altermagnetic order using the magnetic field and the crystallographic angle dependence. Detailed measurements establish that both the longitudinal and transverse electronic responses depend on the relative orientation of the applied current and Néel vector as well as on the crystal orientation and altermagnetic order. These results provide new insights into the interplay between crystal symmetry and altermagnetism for future device applications.

Spin-orbit torque (SOT) magnetization switching is crucial for next-generation energy-efficient spintronic technologies. The recent discovery of van der Waals (vdW) magnets holds promise for such SOT phenomena because of their tunable magnetic properties. However, a demonstration of energy-efficient and field-free SOT switching of vdW magnets is required for their potential applications. Here, we demonstrate field-free and deterministic switching using an intrinsic canted vdW magnet Fe5GeTe2 in a heterostructure with Pt having a larger spin Hall conductivity up to room temperature. Using anomalous Hall electrical detection for magnetization readout, we reveal that field-free deterministic SOT switching in the Fe5GeTe2/Pt Hall devices can be attributed to the canted magnetic anisotropy of Fe5GeTe2, originating from its crystal and magnetic structures. Detailed second harmonic Hall measurements exhibit a high spin Hall conductivity σSH ∼ 3 × 105ℏ/2e Ω-1m-1 with an SOT effective damping-like field of 0.06 mT per MA/cm2. These findings reveal efficient and field-free SOT phenomena in the canted vdW magnet Fe5GeTe2 up to room temperature and highlight their usefulness in spintronic devices.

Current-induced switching of magnetization states in ferromagnet/spin-orbit material heterostructures has attracted significant attention, driven by the increasing need for low power consumption and a more efficient mechanism for magnetization switching. However, current shunting for the used metallic ferromagnets remains challenging in achieving low switching current densities. Thulium iron garnet, Tm3Fe5O12 (TmIG), is promising for such devices as it exhibits strong perpendicular magnetic anisotropy (PMA) and fast magnetization dynamics. However, there still remains a technological challenge in the growth of TmIG films using industry-compatible magnetron sputtering in a simple on-axis geometry for spintronic device applications. Here, we demonstrated the spin-orbit torque (SOT) magnetization switching of TmIG thin film grown by on-axis radio-frequency magnetron sputtering. Robust and deterministic SOT magnetization switching is achieved using TmIG/Pt heterostructures at a current density as low as $$0.7\times {10}^{11}\,{\rm{A}}/{{\rm{m}}}^{2}$$ . Anomalous Hall and second harmonic Hall measurements were performed to quantify effective spin-orbit fields. The effective field inducing damping-like torque is estimated to be 21±1 Oe per 107 A/cm2, higher than previous reports. These findings show a growth method for ferrimagnetic insulators with strong PMA in industry-compatible on-axis sputtering methods and its utilization for achieving energy-efficient SOT non-volatile memory applications.

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have received significant interest for use in tunnel field-effect transistors (TFETs) due to their ultrathin layers and tunable band gap features. In this study, we used density functional theory (DFT) to investigate the electronic properties of six TMD heterostructures, namely, MoSe2/HfS2, MoTe2/ZrS2, MoTe2/HfS2, WSe2/HfS2, WTe2/ZrS2, and WTe2/HfS2, focusing on variations in band alignments. We demonstrate that WTe2/ZrS2 and WTe2/HfS2 have the smallest band gaps (close to 0 or broken) from the considered set. Furthermore, combining DFT with the nonequilibrium Green's function method (DFT-NEGF), we analyzed the output I-V characteristics, revealing increased current as band gap closes across all studied heterostructures. Notably, WTe2/ZrS2 and WTe2/HfS2 show a potential negative differential resistance (NDR) even without a broken gap. Importantly, the inclusion of a p-doped gate effect in WTe2/ZrS2 enhances the current flow and band-to-band tunneling. The rapidly increasing tunneling current under low applied voltage indicates that the WTe2/ZrS2 and WTe2/HfS2 heterostructures are promising for applications in TFETs.

The discovery of van der Waals (vdW) magnetic materials exhibiting non-trivial and tunable magnetic interactions can lead to exotic magnetic states that are not readily attainable with conventional materials. Such vdW magnets can provide a unique platform for studying new magnetic phenomena and realizing magnetization dynamics for energy-efficient and non-volatile spintronic memory and computing technologies. Here, the coexistence of ferromagnetic and antiferromagnetic orders in vdW magnet (Co0.5Fe0.5)5-xGeTe2 (CFGT) above room temperature, inducing an intrinsic exchange bias and canted perpendicular magnetism is discovered. Such non-trivial intrinsic magnetic order enables to realize energy-efficient, magnetic field-free, and deterministic spin-orbit torque (SOT) switching of CFGT in heterostructure with Pt. These experiments, in conjunction with density functional theory and Monte Carlo simulations, demonstrate the coexistence of non-trivial magnetic orders in CFGT, which enables field-free SOT magnetization dynamics in spintronic devices.

Semiconducting transition metal dichalcogenides (TMDs) have attracted significant attention for their potential to develop high-performance, energy-efficient, and nanoscale electronic devices. Despite notable advancements in scaling down the gate and channel length of TMD field-effect transistors (FETs), the fabrication of sub-30 nm narrow channels and devices with atomic-scale edge control still poses challenges. Here, we demonstrate a crystallography-controlled nanostructuring technique to fabricate ultranarrow tungsten disulfide (WS2) nanoribbons as small as sub-10 nm in width. The WS2 nanoribbon junctions having different widths display diodic current-voltage characteristics, providing a way to create and tune nanoscale device properties by controlling the size of the structures. The transport properties of the nanoribbon FETs are primarily governed by narrow channel effects, where the mobility in the narrow channels is limited by edge scattering. Our findings on nanoribbon devices hold potential for developing future-generation nanometer-scale van der Waals semiconductor-based devices and circuits.

Two-dimensional quantum material heterostructures can offer a promising platform for energy-efficient non-volatile spin-based technologies. However, spin dynamics experiments to understand the basic spin-orbit torque phenomena are so far lacking. Here, we demonstrate unconventional out-of-plane magnetization dynamics, and energy-efficient and field-free spin-orbit torque switching in a van der Waals heterostructure comprising out-of-plane magnet Fe3GaTe2 and topological Weyl semimetal TaIrTe4. We measured non-linear second harmonic Hall signal in TaIrTe4/Fe3GaTe2 devices to evaluate the magnetization dynamics, which is characterized by large and tunable out-of-plane damping-like torque. Energy-efficient and deterministic field-free SOT magnetization switching is achieved at room temperature with a very low current density. First-principles calculations unveil the origin of the unconventional charge-spin conversion phenomena, considering the crystal symmetry and electronic structure of TaIrTe4. These results establish that van der Waals heterostructures provide a promising route to energy-efficient, field-free, and tunable spintronic devices.

Spin Hall nano oscillators (SHNOs) are promising candidates for neuromorphic computing due to their miniaturized dimensions, non-linearity, fast dynamics, and ability to synchronize in long chains and arrays. However, tuning the individual SHNOs in large chains/arrays, which is key to implementing synaptic control, has remained a challenge. Here, we demonstrate circular memristive nano-gates, both precisely aligned and shifted with respect to nano-constriction SHNOs of W/CoFeB/HfO x , with increased quality of the device tunability. Gating at the exact center of the nano-constriction region is found to cause irreversible degradation to the oxide layer, resulting in a permanent frequency shift of the auto-oscillating modes. As a remedy, gates shifted outside of the immediate nano-constriction region can tune the frequency dramatically (>200 MHz) without causing any permanent change to the constriction region. Circular memristive nano-gates can, therefore, be used in SHNO chains/arrays to manipulate the synchronization states precisely over large networks of oscillators.

Topological insulators (TIs) are emerging materials for next-generation low-power nanoelectronic and spintronic device applications. TIs possess non-trivial spin-momentum locking features in the topological surface states in addition to the spin-Hall effect (SHE), and Rashba states due to high spin-orbit coupling (SOC) properties. These phenomena are vital for observing the charge-spin conversion (CSC) processes for spin-based memory, logic and quantum technologies. Although CSC has been observed in TIs by potentiometric measurements, reliable nonlocal detection has so far been limited to cryogenic temperatures up to T = 15 K. Here, we report nonlocal detection of CSC and its inverse effect in the TI compound Bi1.5Sb0.5Te1.7Se1.3 at room temperature using a van der Waals heterostructure with a graphene spin-valve device. The lateral nonlocal device design with graphene allows observation of both spin-switch and Hanle spin precession signals for generation, injection and detection of spin currents by the TI. Detailed bias- and gate-dependent measurements in different geometries prove the robustness of the CSC effects in the TI. These findings demonstrate the possibility of using topological materials to make all-electrical room-temperature spintronic devices.

Dirac fermions, particles with zero rest mass, are believed to play a key role in the exotic science and the advancement of quantum technology. Their proximity to correlated electrons leads to kink (waterfall) in the Dirac bands.

Atomically thin 2D films and their van der Waals heterostructures have demonstrated immense potential for breakthroughs and innovations in science and technology. Integrating 2D films into electronics and optoelectronics devices and their applications in electronics and optoelectronics can lead to improve device efficiencies and tunability. Consequently, there has been steady progress in large-area 2D films for both front- and back-end technologies, with a keen interest in optimizing different growth and synthetic techniques. Parallelly, a significant amount of attention has been directed toward efficient transfer techniques of 2D films on different substrates. Current methods for synthesizing 2D films often involve high-temperature synthesis, precursors, and growth stimulants with highly chemical reactivity. This limitation hinders the widespread applications of 2D films. As a result, reports concerning transfer strategies of 2D films from bare substrates to target substrates have proliferated, showcasing varying degrees of cleanliness, surface damage, and material uniformity. This review aims to evaluate, discuss, and provide an overview of the most advanced transfer methods to date, encompassing wet, dry, and quasi-dry transfer methods. The processes, mechanisms, and pros and cons of each transfer method are critically summarized. Furthermore, we discuss the feasibility of these 2D film transfer methods, concerning their applications in devices and various technology platforms.

The layered van der Waals material ZrTe5 is known as a candidate topological insulator (TI), however its topological phase and the relation with other properties such as an apparent Dirac semimetallic state is still a subject of debate. We employ a semiclassical multicarrier transport (MCT) model to analyze the magnetotransport of ZrTe5 nanodevices at hydrostatic pressures up to 2 GPa. The temperature dependence of the MCT results between 10 and 300 K is assessed in the context of thermal activation, and we obtain the positions of conduction and valence band edges in the vicinity of the chemical potential. We find evidence of the closing and re-opening of the band gap with increasing pressure, which is consistent with a phase transition from weak to strong TI. This matches expectations from ab initio band structure calculations, as well as previous observations that CVT-grown ZrTe5 is a weak TI in ambient conditions.

Abstract The unique electronic properties of topological quantum materials, such as protected surface states and exotic quasiparticles, can provide an out-of-plane spin-polarized current needed for external field-free magnetization switching of magnets with perpendicular magnetic anisotropy. Conventional spin–orbit torque (SOT) materials provide only an in-plane spin-polarized current, and recently explored materials with lower crystal symmetries provide very low out-of-plane spin-polarized current components, which are not suitable for energy-efficient SOT applications. Here, we demonstrate a large out-of-plane damping-like SOT at room temperature using the topological Weyl semimetal candidate TaIrTe4 with a lower crystal symmetry. We performed spin–torque ferromagnetic resonance (STFMR) and second harmonic Hall measurements on devices based on TaIrTe4/Ni80Fe20 heterostructures and observed a large out-of-plane damping-like SOT efficiency. The out-of-plane spin Hall conductivity is estimated to be (4.05 ± 0.23)×104 (ℏ ⁄ 2e) (Ωm)−1, which is an order of magnitude higher than the reported values in other materials.

AbstractThermal conductivity enhancement in polymers is vital for advanced applications. This study introduces a novel method to align hexagonal boron nitride (hBN) nanosheets within polydimethylsiloxane (PDMS) matrices using a Halbach array to create a highly uniform magnetic field. This technique achieves significant improvements in thermal conductivity by effectively aligning hBN nanosheets. This research shows that hBN nanosheets, when aligned, can drastically enhance thermal conductivity in PDMS composites. Specifically, 10 wt.% vertically aligned hBN nanosheets in a rotating magnetic field achieve a thermal conductivity of 3.58 W mK−1, an impressive 1950% increase over pure PDMS. Additionally, the study explores the effects of orientation on dielectric properties, finding that the orientation of hBN nanosheets also improves electrical insulation and increases the dielectric constant while maintaining extremely low dielectric losses. For a vertically oriented sample, the dielectric constant reaches ≈14, and dielectric losses are as low as 0.0049 at 100 Hz, highlighting their potential for energy storage capacitors. This approach not only enhances thermal management but also maintains or improves electrical insulation, offering promising advances for polymer composites in various technological applications.