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Magnetocaloric effect (MCE) exhibits highly efficient and ecological cooling abilities for solid-state refrigeration in contrast to traditional vapor-compression refrigeration. Successive emerging two-dimensional (2D) magnetic materials provide a fertile platform for exploring low-dimensional MCE systems. Here, we focus on a series of 2D transition metal dihalides MX2 (M = Fe, Ru, Os; X = Cl, Br) to explore the maximum isothermal magnetic entropy change (− Δ S mag max ) and adiabatic temperature change (Δ T ad max ) under external magnetic field. It is found that FeCl2, FeBr2, and RuCl2 have intrinsically sizable − Δ S mag max , Δ T ad max , and high thermal conductivity near room temperature, demonstrating superior comprehensive refrigeration performance in comparison with other 2D magnets. It is revealed that strong nearest-neighbor ferromagnetic exchange interaction plays a decisive role in − Δ S mag max , and the high lattice thermal conductivities of FeCl2 and RuCl2 are attributed to the longer phonon lifetime and larger group velocity of low-frequency acoustic branch. Moreover, moderate strain and carriers doping are able to effectively regulate Curie temperature and magnetocrystalline anisotropy energy and correspondingly enhance − Δ S mag max . The present work provides important insights for the exploration of 2D magnets for magnetocaloric refrigeration near room temperature. [ABSTRACT FROM AUTHOR]

The Dzyaloshinskii–Moriya interactions (DMIs) of Cr2O2ClI Janus monolayer are investigated using the first‐principles calculations. There are three DMI mechanisms (namely, the Half–Fert–Levy mechanism, the Fert–Levy mechanism, and the Rashba mechanism) in Cr2O2ClI Janus monolayer. The Half–Fert–Levy mechanism, by which the I atoms enhance the spin orbit coupling interaction on the type‐I Cr atoms but have no such effect on the type‐II Cr atoms, contributes to the y‐component of the DMI vector between two nearest‐neighbor Cr atoms. Originating from the strong spin orbit coupling interaction of the I atoms, the Fert–Levy mechanism results in a significant DMI vector via the Cr–I–Cr exchange path between two type‐I next‐nearest‐neighbor Cr atoms. Induced by the intrinsic electric field of the Janus structure, the Rashba mechanism results in nonzero in‐plane components of the DMI vectors. This work provides the first‐principles calculations of the DMIs of Cr2O2ClI Janus monolayer and reveals insight into the physics behind the calculated DMIs, which promote the understanding of the complicated DMIs due to multiple mechanisms in 2D magnetic Janus monolayers. [ABSTRACT FROM AUTHOR]

Modern electronic devices are moving toward miniaturization and integration. Therefore, achieving electrical control of magnetization effectively in 1D materials represents a promising field for the practical applications in memory elements. Herein, it is discovered, from first‐principles calculations, that an electric‐field‐tunable bipolar linear magnetoelectric effect can be realized in 1D antiferromagnets based on double‐Gd‐adsorbed graphene nanoribbon with four zigzag carbon chains (2Gd‐4ZGNR). It is found that, compared with the bare 4ZGNR, the adsorption of two Gd atoms on the 4ZGNR reduces the bandgap. As a result, 2Gd‐4ZGNR transits from antiferromagnetic semiconductor to ferrimagnetic metal at a relatively low critical external transverse (perpendicular) electric field, where the net magnetic moment can be induced. The antiferromagnetism and inversion‐symmetrical crystal structure further allow to realize a bipolar linear magnetoelectric effect, where the 2Gd‐4ZGNR forms two groups of independent linear magnetic response states, acting as a magnetoelectric memory element. [ABSTRACT FROM AUTHOR]

The present study systematically investigated the effects of a laser welding speed and a defocusing amount on the microstructure and mechanical properties of low alloy high strength Q345 steel joints. The macro-morphology, microstructure, Vickers microhardness, and tensile properties of as-welded joints were analyzed. The results indicated a significant correlation between the laser welding speed and the size of individual zones within the welded joint. As the laser welding speed increased, the size of each zone decreased noticeably. The microstructure of the fusion zone was composed of proeutectoid ferrite, ferrite side-plate, and acicular ferrite. An increase in welding speed and defocusing amount facilitated microstructural changes towards formation of ferrite side-plate and acicular ferrite. Maximum tensile strength and maximum elongation of as welded joints were measured to be 669 MPa and 21.8%, respectively. The joints with maximum tensile strength tended to fracture within the fusion zone. The increase in welding speed and defocusing amount caused a significant decrease in normalized enthalpy and volumetric energy density. [ABSTRACT FROM AUTHOR]

Magnetic units with large magnetic anisotropy energy (MAE) and high Curie temperature (Tc) are crucial for spintronic and quantum computing devices, which are a persisting demand for miniaturization of magnetic units. Using first-principles calculations and Monte Carlo simulation, it is found that monolayer 1T-CrTe2 exhibits strong perpendicular magnetic anisotropy with a MAE of approximately 5.29 meV and high Tc of ∼136 K. Interestingly, we find that the MAE and Tc of monolayer 1T-CrTe2 are tunable through electron/hole doping, strain, and heterostructure engineering. The magnetic easy-axis can be adjusted from out of plane to in plane, which is mainly attributed to the coupling between Te atomic orbitals ( p x , p y ). Second-order perturbation theory reveals that the spin–orbit coupling interaction between the occupied p x and unoccupied p y orbitals in opposite spin channel near Fermi level gives rise to negative contribution of MAE. Moreover, Tc can be enhanced to ∼230 K through super–superexchange mechanism of heterostructure due to the electron hopping between t 2 g / e g orbitals of Cr4+ ions and e 1 / a 1 orbitals of Fe2+ ions. Importantly, we find that Tc can be boosted above room temperature by applying moderate strain (6%), ascribing to significant enhancement of MAE and exchange coupling constant. The present work indicates that monolayer 1T-CrTe2-based two-dimensional materials are very promising for room temperature application in magnetic storage and information processing. [ABSTRACT FROM AUTHOR]

In the context of the national strategy of high-quality development of the Yellow River Basin, studying the distribution characteristics, environmental behavior and the ecological risks of emerging pollutants in the sediments of the Yellow River Basin is an important basis for improving the environmental pollution control system and the water environment of the basin. This paper discusses the distribution characteristics and sources of emerging pollutants in the sediments of the Yellow River Basin, expounds their environmental behavior and ecological risk, and proposes the future research directions, namely, the monitoring and traceability of emerging pollutants, the multi-media and multi-path environmental behavior and fate of emerging pollutants in sediments, the composite pollution mechanism of emerging pollutants in sediments, ecological risk and control, etc., which would provide a reference for pollution control and water environment protection in the Yellow River Basin. [ABSTRACT FROM AUTHOR]