Temperature-dependent magnetic properties of the room-temperature ferromagnetic Janus monolayer Fe2XY (X, Y = I, Br, Cl; X ≠ Y).

Excellent magnetic properties at room temperature are crucial for the application of ferromagnets in spintronic and topological quantum devices. Using first-principles calculations and atomistic spin model simulations, we investigate the temperature-dependent magnetic properties of the Janus monolayer Fe2XY (X, Y = I, Br, Cl; X ≠ Y), as well as the effects of different magnetic interactions within the next-nearest-neighbor shell on the Curie temperature (TC). A large isotropic exchange interaction between one Fe atom and its next-nearest-neighbor counterparts can significantly increase the TC, while an antisymmetric exchange interaction decreases it. More importantly, we employ the temperature rescaling method, which can obtain temperature-dependent magnetic properties quantitatively consistent with experimental values, and find that the effective uniaxial anisotropy constant and coercive field decrease with increasing temperature. Moreover, at room temperature, Fe2IY is a rectangular-loop magnetic material with a giant coercive field up to ∼8 T, demonstrating its potential for application in room-temperature memory devices. Our findings can advance the application of these Janus monolayers in room-temperature spintronic devices and through heat-assisted techniques.

Promising ultra-short channel transistors based on OM2S (M = Ga, In) monolayers for high performance and low power consumption.

It is hoped that two-dimensional (2D) semiconductors overcome the short channel effect and continue Moore's law. However, 2D material-based ultra-short channel devices still face the challenge of simultaneously achieving high-performance (HP) and low-power (LP) consumption. Here, we theoretically designed monolayer OM2S (M = Ga, In)-based metal-oxide-semiconductor field-effect transistors (MOSFETs), considering the gate length from 1 to 5 nm, doping concentration and underlap structure. We found that in HP (LP) applications, the on-state current exceeds 1000 (500) µA µm-1 under a 1 nm (2 nm) gate length, surpassing the needs of the International Technology Roadmap for Semiconductors (ITRS) in 2028. The subthreshold swing is close to the Boltzmann tyranny (60 mV dec-1) even as the gate length shrinks to 2 nm. The energy-delay product is two orders lower than 1.02 × 10-28 J s µm-1, indicating extraordinary high-speed manipulation and low-energy expending. Therefore, monolayer OM2S has great application in ultra-short scale devices with HP and LP consumption, and can be taken as a candidate to extend Moore's Law.

Effects of p-d orbital mixings on magnetocrystalline anisotropy for D3d-symmetric ferromagnetic semiconducting monolayers.

Understanding magnetic anisotropy based on electronic properties is vital for theoretical and applied research on ferromagnetic semiconductors. Here, for several representative D3d-symmetric ferromagnetic semiconducting monolayers, we investigate the effects of mixings between d-orbitals of central magnetic atoms and p-orbitals of ligands on magnetocrystalline anisotropy energy (MAE). For high-spin materials, the weakening of p-d mixing increases the electron occupation of spin-up bonding d-orbitals at the expense of the electron occupation in the corresponding spin-down orbitals, In contrast, the weakening of p-d mixing decreases the electron occupation of the spin-up antibonding d-orbitals and enhances the electron occupation in the corresponding spin-down orbitals. The weakening mixings also result in an overall shift of the spin-down band toward a higher energy with respect to the spin-up band. These changes are just the opposite in a low-spin material. More interestingly, we find that the transition point between the bonding and the antibonding spin-up bands plays a significant role in tuning the MAE. Its shift with strain is almost linearly related to the p-d bond strength and significantly affects both the electron occupation of occupied spin-up antibonding d-bands and the band shift of unoccupied spin-up d-bands. Furthermore, the correlation of these mixing-related changes in electronic structures with the MAE is qualitatively and quantitatively analyzed. Our findings can deepen the understanding of the correlation between MAE and p-d orbital mixings and provide theoretical guidance for modulating the MAE.

Magnetoelectric coupling effects on the band alignments of multiferroic In2Se3-CrI3 trilayer heterostructures.

Due to unique magnetoelectric coupling effects, two-dimensional (2D) multiferroic van der Waals heterostructures (vdWHs) are promising for next-generation information processing and storage devices. Here, we design theoretically multiferroic In2Se3/CrI3 trilayer vdWHs with different stacking patterns. For the CrI3/In2Se3/CrI3 trilayer vdWHs, whether ferroelectric upward or downward polarization, type-I and type-II band alignments are formed for spin-up and spin-down channels. However, for the CrI3/In2Se3/In2Se3 trilayer vdWHs, downward polarization induces the type-III band alignment, which is typical for spin-tunnel transistors. Moreover, nonvolatile ferroelectric polarization and stacking patterns can induce the conversion between a unipolar semiconductor and a bipolar (unipolar) half-metal. These results provide a possible route to realize nanoscale multifunctional spintronic devices based on 2D multiferroic systems.

Band offset trends in IV-VI layered semiconductor heterojunctions.

The band offsets between semiconductors are significantly associated with the optoelectronic characteristics and devices design. Here, we investigate the band offset trends of few-layer and bulk IV-VI semiconductors MX and MX2(M = Ge, Sn; X = S, Se, Te). For common-cation (anion) systems, as the atomic number increases, the valence band offset of MX decreases, while that of MX2has no distinct change, and the physical origin can be interpreted using band coupling mechanism and atomic potential trend. The band edges of GeX2system straddle redox potentials of water, making them competitive candidates for photocatalyst. Moreover, layer number modulation can induce the band offset of GeSe/SnS and GeSe2/GeS2heterojunction undergoing a transition from type I to type II, which makes them suitable for optoelectronic applications.