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Europium (Eu) metal has a body centered cubic crystal structure which, upon a paramagnetic-to-helical magnetic phase transition, undergoes a body centered tetragonal distortion. The magnetic helix appears below a Néel temperature (TN) of ∼90 K, and an applied magnetic field gives rise to conical magnet structure. We have prepared Eu metal thin films on Si (001) substrates using Eu metal as a target by pulsed laser deposition and studied the transport properties by a four-probe method. The resistance shows a sudden slope change at TN of 88 K. The magnetoresistance (MR) is positive at temperatures below 30 K and exhibits negative values above that. Our analyses show that the positive MR at low temperatures originates from magnetic field induced spin fluctuation, and the negative MR at higher temperature is a result of suppression of critical spin fluctuation of the Eu spins by the magnetic field. The Eu film also shows hysteretic MR behaviors in mid field range, which is a result of re-distribution of the helical antiferromagnetic domains by the magnetic fields. We have also studied the transverse magnetotransport in the Eu thin films. The observed anomalous Hall effect is believed to be associated with the magnetic moment induced by the field or due to the helical spin structure of Eu itself. 

Leveraging the reciprocal-space proximity effect between superconducting bulk and topological surface states (TSSs) offers a promising way to topological superconductivity. However, elucidating the mutual influence of bulk and TSSs on topological superconductivity remains a challenge. Here, we report pioneering transport evidence of a thickness-dependent transition from conventional to unconventional superconductivity in 2M-phase WS2 (2M-WS2). As the sample thickness reduces, we see clear changes in key superconducting metrics, including critical temperature, critical current, and carrier density. Notably, while thick 2M-WS2 samples show conventional superconductivity, with an in-plane (IP) upper critical field constrained by the Pauli limit, samples under 20 nm exhibit a pronounced IP critical field enhancement, inversely correlated with 2D carrier density. This marks a distinct crossover to unconventional superconductivity with strong spin-orbit-parity coupling. Our findings underscore the crucial role of sample thickness in accessing topological states in 2D topological superconductors, offering pivotal insights into future studies of topological superconductivity. 

Recent research has demonstrated the potential for topological superconductivity, anisotropic Majorana bound states, optical nonlinearity, and enhanced electrochemical activity for transition metal dichalcogenides (TMDs) with a 2M structure. These unique TMD compounds exhibit metastability and, upon heating, undergo a transition to the thermodynamically stable 2H phase. The 2M phase is commonly made at high temperatures using traditional solid-state methods, and this metastability further complicates the growth of large 2M WS2 crystals. Herein, a novel synthetic method was developed, focusing on a molten salt reaction to synthesize large 2H crystals and then inducing transformation to the 2M phase through intercalation and thermal treatment. The 2H crystals were intercalated via a room-temperature sodium naphthalenide solution, producing a previously unreported Na-intercalated 2H WS2 phase. Thermal heating was required to facilitate the phase transition to the intercalated 2M crystal structure. This phase transition was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), electron dispersive X-ray spectroscopy (EDS), and Raman spectroscopy, which confirmed the synthesis of the intercalated 2M phase. Upon deintercalation, crystal and powder samples showed superconductivity with a Tc of 8.6–8.7 K, similar to previously reported values. The generality of this process was further demonstrated using alkali metal triethyl borohydride to intercalate 2H WS2 and produced the desired 2M phase. This novel synthetic method has broad implications for discovering metastable phases in other TMD families and layered materials. Separation of the intercalation and phase transition also has the potential to allow for large-scale synthesis of this technologically important phase with greater control over each step of the reaction. 

Abstract The investigation of exotic properties in two-dimensional (2D) topological superconductors has garnered increasing attention in condensed matter physics, particularly for applications in topological qubits. Despite this interest, a reliable way of fabricating topological Josephson junctions (JJs) utilizing topological superconductors has yet to be demonstrated. Controllable structural phase transition presents a unique approach to achieving topological JJs in atomically thin 2D topological superconductors. In this work, we report the pioneering demonstration of a structural phase transition from the superconducting to the semiconducting phase in the 2D topological superconductor 2M-WS₂. We reveal that the metastable 2M phase of WS₂remains stable in ambient conditions but transitions to the 2H phase when subjected to temperatures above 150 °C. We further locally induced the 2H phase within 2M-WS₂nanolayers using laser irradiation. Notably, the 2H phase region exhibits a hexagonal shape, and scanning tunneling microscopy uncovers an atomically sharp crystal structural transition between the 2H and 2M phase regions. Moreover, the 2M to 2H phase transition can be induced at the nanometer scale by a 200 kV electron beam. The electrical transport measurements further confirmed the superconductivity of the pristine 2M-WS₂and the semiconducting behavior of the laser-irradiated 2M-WS₂. Our results establish a novel approach for controllable topological phase change in 2D topological superconductors, significantly impacting the development of atomically scaled planar topological JJs. 

Abstract Effective control of magnetic phases in two-dimensional magnets would constitute crucial progress in spintronics, holding great potential for future computing technologies. Here, we report a new approach of leveraging tunneling current as a tool for controlling spin states in CrI₃. We reveal that a tunneling current can deterministically switch between spin-parallel and spin-antiparallel states in few-layer CrI₃, depending on the polarity and amplitude of the current. We propose a mechanism involving nonequilibrium spin accumulation in the graphene electrodes in contact with the CrI₃layers. We further demonstrate tunneling current-tunable stochastic switching between multiple spin states of the CrI₃tunnel devices, which goes beyond conventional bi-stable stochastic magnetic tunnel junctions and has not been documented in two-dimensional magnets. Our findings not only address the existing knowledge gap concerning the influence of tunneling currents in controlling the magnetism in two-dimensional magnets, but also unlock possibilities for energy-efficient probabilistic and neuromorphic computing. 

Background: Magnetic nanoparticles are attracting much attention toward easyoperation and size controllable synthesis methods. We develop a method to synthesize MnO, Co,CoO, and Ni nanoparticles by thermal decomposition of metal 2,4-pentanedionates in the presenceof oleylamine (OLA), oleic acid (OA), and 1-octadecene (ODE). Methods: Similar experimental conditions are used to prepare nanoparticles except for the metalstarting materials (manganese 2,4-pentanedionate, nickel 2,4-pentanedionate, and cobalt 2,4-pentanedionate), leading to different products. For the manganese 2,4-pentanedionate startingmaterial, MnO nanoparticles are always obtained as the reaction is controlled with differenttemperatures, precursor concentrations, ligand ratios, and reaction time. For the cobalt 2,4-pentanedionate starting material, only three experimental conditions can produce pure phase CoOand Co nanoparticles. For the nickel 2,4-pentanedionate starting material, only three experimentalconditions lead to the production of pure phase Ni nanoparticles. Results: The nanoparticle sizes increase with the increase of reaction temperatures. It is observedthat the reaction time affects nanoparticle growth. The nanoparticles are studied by XRD, TEM,and magnetic measurements. Conclusion: This work presents a facile method to prepare nanoparticles with different sizes,which provides a fundamental understanding of nanoparticle growth in solution.