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Two-dimensional ferromagnet Cr 2 Ge 2 Te 6 (CGT) is so resistive below its Curie temperature that probing its magnetism by electrical transport becomes extremely difficult. By forming heterostructures with Pt, however, we observe clear anomalous Hall effect (AHE) in 5 nm thick Pt deposited on thin (< 50 nm) exfoliated flakes of CGT. The AHE hysteresis loops persist to ~ 60 K, which matches well to the Curie temperature of CGT obtained from the bulk magnetization measurements. The slanted AHE loops with a narrow opening indicate magnetic domain formation, which is confirmed by low-temperature magnetic force microscopy (MFM) imaging. These results clearly demonstrate that CGT imprints its magnetization in the AHE signal of the Pt layer. Density functional theory calculations of CGT/Pt heterostructures suggest that the induced ferromagnetism in Pt may be primarily responsible for the observed AHE. Our results establish a powerful way of investigating magnetism in 2D insulating ferromagnets which can potentially work for monolayer devices.

To magnetize surfaces of topological insulators without damaging their topological feature is a crucial step for the realization of the quantum anomalous Hall effect (QAHE) and remains as a challenging task. Through density functional calculations, we found that adsorption of a semiconducting two-dimensional van der Waals (2D-vdW) ferromagnetic CrI3 monolayer can create a sizable spin splitting at the Dirac point of the topological surface states of Bi2Se3 films. Furthermore, general rules that connect different quantum and topological parameters are established through model analyses. This work provides a useful guideline for the realization of QAHE at high temperatures in heterostructures of 2D-vdW magnetic monolayers and topological insulators.

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Since catalytic performance of platinum-metal (Pt-M) nanoparticles is primarily determined by the chemical and structural configurations of the outermost atomic layers, detailed knowledge of the distribution of Pt and M surface atoms is crucial for the design of Pt-M electrocatalysts with optimum activity. Further, an understanding of how the surface composition and structure of electrocatalysts may be controlled by external means is useful for their efficient production. Here, we report our study of surface composition and the dynamics involved in facet-dependent oxidation of equilibrium-shaped PtCo nanoparticles in an initially disordered state via in situ transmission electron microscopy and density functional calculations. In brief, using our advanced in situ gas cell technique, evolution of the surface of the PtCo nanoparticles was monitored at the atomic scale during their exposure to an oxygen atmosphere at elevated temperature, and it was found that Co segregation and oxidation take place on {111} surfaces but not on {100} surfaces.

The intrinsic spin-dependent transport properties of two types of lateral VS2|MoS2 heterojunctions are systematically investigated using first-principles calculations, and their various nanodevices with novel properties are designed. The lateral VS2|MoS2 heterojunction diodes show a perfect rectifying effect and are promising for the applications of Schottky diodes. A large spin-polarization ratio is observed for the A-type device and pure spin-mediated current is then realized. The gate voltage significantly tunes the current and rectification ratio of their field-effect transistors (FETs). In addition, they all have sensitive photoresponse to blue light, and could be used as photodetector and photovoltaic device. Moreover, they generate the effective thermally-driven current when a temperature gratitude appears between the two terminals, suggesting them as potential thermoelectric materials.Hence, the lateral VS2|MoS2 heterojunctions show a multifunctional nature and have various potential applications in spintronics, optoelectronics, and spin caloritronics.

Recent experiments reveal that the honeycomb ruthenium trichloride -RuCl 3 is a prime candidate of the Kitaev quantum spin liquid (QSL). However, there is no theoretical model which can properly describe its experimental dynamical response, due to the lack of a full understanding of its magnetic interactions. Here, we propose a general scheme to calculate the magnetic interactions in systems (e.g., -RuCl 3 ) with non-negligible orbital moments by constraining the directions of orbital moments. With this scheme, we put forward a minimal J 1 -K 1 -1 -J 3 -K 3 model for -RuCl 3 and find that: (I) The third nearest neighbor (NN) antiferromagnetic Heisenberg interaction J 3 stabilizes the zigzag antiferromagnetic order; (II) The NN symmetric off-diagonal exchange 1 plays a pivotal role in determining the preferred direction of magnetic moments and generating the spin wave gap. Exact diagonalization study on this model shows that the Kitaev QSL can be realized by suppressing the NN symmetric off-diagonal exchange 1 and the third NN Heisenberg interaction J 3 . Thus, we not only propose a powerful general scheme for investigating the intriguing magnetism of J eff =1/2 magnets, but also point out future directions for realizing the Kitaev QSL in the honeycomb ruthenium trichloride -RuCl 3 . 71.15.Am, 75.50.Ee, 75.30.Ds, 02.70.Uu Introduction.−Quantum spin liquid is one of the most exotic and elusive topological states of frustrated magnets showing remarkable collective phenomena, such as emergent gauge fields and fractional particle excitations [1][2][3]. Of particular interest is the S=1/2 Kitaev model on the honeycomb lattice which has an exactly solvable QSL ground state [4]. It was proposed that such model may be realized by the J eff =1/2 state in the honeycomb iridium oxides, for instance, Na 2 IrO 3 and -Li 2 IrO 3 [5-10]. Unfortunately, various experiments show that Na 2 IrO 3 has a zigzag antiferromagnetic (AFM) order below 15 K [5,9,10] while -Li 2 IrO 3 has an incommensurate counter-rotating magnetic order [11]. PACS number(s):Excitingly, some up-to-date experiments [2,12,13] indicate that the honeycomb ruthenium trichloride -RuCl 3 is closer to the Kitaev QSL than the widely studied iridium oxides. It has been demonstrated that -RuCl 3 exhibits frustrated magnetic interactions [12] and can be described by the J eff =1/2 state [13,14] which is the prerequisite for realizing the Kitaev model. Most importantly, Banerjee et al. reported that -RuCl 3 is a proximate Kitaev QSL magnet because its dynamical response measurements above interlayer energy scale are explained in terms of deconfinement physics expected for the QSL [2]. 3 4 2 2 6.4 E J J K K J K

Two-dimensional (2D) magnetic materials are essential for the development of the next-generation spintronic technologies. Recently, layered van der Waals (vdW) compound MnBi2Te4 (MBT) has attracted great interest, and its 2D structure has been reported to host coexisting magnetism and topology. Here, we design several conceptual nanodevices based on MBT monolayer (MBT-ML) and reveal their spin-dependent transport properties by means of the first-principles calculations. The pn-junction diodes and sub-3-nm pin-junction field-effect transistors (FETs) show a strong rectifying effect and a spin filtering effect, with an ideality factor n close to 1 even at a reasonably high temperature. In addition, the pip- and nin-junction FETs give an interesting negative differential resistive (NDR) effect. The gate voltages can tune currents through these FETs in a large range. Furthermore, the MBT-ML has a strong response to light. Our results uncover the multifunctional nature of MBT-ML, pave the road for its applications in diverse next-generation semiconductor spin electric devices.