Abstract ：

Two-dimensional (2D) layered materials have been studied in depth during the past two decades due to their unique structure and properties. Transition metal (TM) intercalation of layered materials have been proven as an effective way to introduce new physical properties, such as tunable 2D magnetism, but the direct growth of atomically thin heteroatoms-intercalated layered materials remains untapped. Herein, we directly synthesize various ultrathin heteroatoms-intercalated 2D layered materials (UHI-2DMs) through flux-assisted growth (FAG) approach. Eight UHI-2DMs (V1/3NbS2, Cr1/3NbS2, Mn1/3NbS2, Fe1/3NbS2, Co1/3NbS2, Co1/3NbSe2, Fe1/3TaS2, Fe1/4TaS2) were successfully synthesized. Their thickness can be reduced to the thinnest limit (bilayer 2D material with monolayer intercalated TM), and magnetic ordering can be induced in the synthesized structures. Interestingly, due to the possible anisotropy-stabilized long-range ferromagnetism in Fe1/3TaS2 with weak interlayer coupling, the layer-independent magnetic ordering temperature of Fe1/3TaS2 was revealed by magneto-transport properties. This work establishes a general method for direct synthesis of heteroatom-intercalated ultrathin 2D materials with tunable chemical and physical properties. The intercalation of heteroatoms has been demonstrated to be an effective approach to introduce new physical properties in 2D layered materials (2DMs). Here, the authors report a flux-assisted growth method to synthesize various ultrathin heteroatoms-intercalated 2DMs, showing evidence of anisotropy-stabilized long-range ferromagnetism in Fe1/3TaS2.

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Abstract ：

The discovery of room-temperature ferromagnetism in van der Waals (vdW) materials opens new avenues for exploring low-dimensional magnetism and its applications in spintronics. Recently, the observation of the room-temperature topological Hall effect in the vdW ferromagnet Fe3GaTe2 suggests the possible existence of room-temperature skyrmions, yet skyrmions have not been directly observed. In this study, real-space imaging was employed to investigate the domain evolution of the labyrinth and skyrmion structure. First, Neel-type skyrmions can be created at room temperature. In addition, the influence of flake thickness and external magnetic field (during field cooling) on both labyrinth domains and the skyrmion lattice is unveiled. Due to the competition between magnetic anisotropy and dipole interactions, the specimen thickness significantly influences the density of skyrmions. These findings demonstrate that Fe3GaTe2 can host room-temperature skyrmions of various sizes, opening up avenues for further study of magnetic topological textures at room temperature.

Keyword ：

magnetic domain magnetic force microscope van der Waals magnet Fe3GaTe2

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This work demonstrates that Mn can be a beneficial candidate for the performance modulation of permanent magnetic materials like SmCo 5 . Theoretical calculations reveal that Mn has a large positive contribution to the magnetization of SmCo 5 , owing to the strong ferromagnetic exchange interaction between Co and Mn atoms. It is also found that Mn could occupy both 2 c and 3 g crystal sites because of the minute energy difference between them can be easily overcome through thermal activation. Co atoms on the same site with Mn have increasing moments with the increase in Mn content, whereas those on the other sites show decreasing moments. The experimental substitution of Mn for Co leads to a contraction of the SmCo 5 single-phase region, and thus pure Sm (Co, Mn) 5 phase could only be obtained through subtle control of Sm content by annealing. Significantly, a 13 % increase in saturation magnetization of SmCo 5 is achieved through Mn substitution. A slight rise in the Curie temperature is also obtained, suggesting that Mn substitution does not strongly disturb the exchange interactions of the Co sublattice. This study offers a new option for enhancing magnetic properties in Sm-Co systems and introduces novel physical phenomena resulting from Mn substitution, which is worthy of further investigation.

Keyword ：

Magnetization enhancement SmCo5 permanent magnet Ferromagnetic exchange interaction Phase stability

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Parallel nanomaterials possess unique properties and show potential applications in industry. Whereas, vertically aligned 2D nanomaterials have plane orientations that are generally chaotic. Simultaneous control of their growth direction and spatial orientation for parallel nanosheets remains a big challenge. Here, a facile preparation of vertically aligned parallel nanosheet arrays of aluminum-cobalt oxide is reported via a collaborative dealloying and hydrothermal method. The parallel growth of nanosheets is attributed to the lattice-matching among the nanosheets, the buffer layer, and the substrate, which is verified by a careful transmission electron microscopy study. Furthermore, the aluminum-cobalt oxide nanosheets exhibit high-temperature ferromagnetism with a 919 K Curie temperature and a 5.22 emu g(-1) saturation magnetization at 300 K, implying the potential applications in high-temperature ferromagnetic fields.

Keyword ：

parallel nanosheet arrays high-temperature ferromagnetism 2D nanomaterials lattice-matching

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The term Ferrofluids is used to refer to the coherent colloidal suspension of nanometer size ferromagnetic particles or their oxides in base fluids such as oil, water etc. Due to decrease in size to nanometric level, the property of ferromagnetism shifts towards super-magnetism. It creates an opportunity to modify the thermophysical parameters of magnetic nanofluid when exposed to exterior magnetization field. A plethora of research on Ferrofluids has made way for varied applications ranging from dynamic loudspeakers, computer hard drives to room cleaning robots which exploit their exceptional operating characteristics. The field of thermal engineering in relation to the applications of ferrofluids have been explored extensively in the recent past. Innovative outlooks relating to thermal control of miniaturized systems have opened. Major properties which are under study by researchers are related to area of enhanced thermal conductivity along with improvement in thermal performance of the magnetic nanofluid. These studies involve analysis pertaining ferrofluid's heat transfer along with the controlling of parameters when external magnetic field is present. The alternative solutions to heat transfer can be provided with ferrofluids having improved thermal conductivity and the ability to externally control and change heat transfer coefficient. At present, the power supplied to miniaturized systems is being provided through batteries which have several limitations such as big size, shorter lifetime, holding hazardous and unsafe materials and troubles in replacement. Due to these limitations, an energy harvester based upon ferrofluid could provide an alternative source of energy. Recent studies also focus on the development of energy based harvester based upon vibrations. In this context, this paper will try to provide a wide-ranging review of present and developing applications of ferrofluids with special focus on the study of heat transfer and energy harvesters.

Keyword ：

Energy harvester Hybrid nanofluids Magnetism Ferro-magnetic fluids Heat transfer enhancement

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The quest for pragmatic room-temperature (RT) magnetic semiconductors (MSs) with a suitable bandgap constitutes one of the contemporary opportunities to be exploited. This may provide a materials platform for to bring new-generation ideal information device technologies into real-world applications where the otherwise conventionally separately utilized charge and spin are simultaneously exploited. Here we present RT ferromagnetism in an Fe-doped SnSe (Fe:SnSe) van der Waals (vdW) single crystalline ferromagnetic semiconductor (FMS) with a semiconducting bandgap of similar to 1.19 eV (comparable to those of Si and GaAs). The synthesized Fe:SnSe single crystals feature a dilute Fe content of <1.0 at%, a Curie temperature of similar to 310 K, a layered vdW structure nearly identical to that of pristine SnSe, and the absence of in-gap defect states. The Fe:SnSe vdW diluted magnetic semiconductor (DMS) single crystals are grown using a simple temperature-gradient melt-growth process, in which the magnetic Fe atom doping is realized uniquely using FeI2 as the dopant precursor whose melting point is low with respect to crystal growth, and which in principle possesses industrially unlimited scalability. Our work adds a new member in the family of long-searching RT magnetic semiconductors, and may establish a generalized strategy for large-volume production of related DMSs.

Keyword ：

Curie temperature Fe-doped SnSe Room-temperature ferromagnetism Semiconducting energy gap Magnetic semiconductor

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Evolution of diverse Hall effects due to successive magnetic transitions has been observed in Mn2.5Fe0.6Sn0.9 by suitable chemical substitution of Fe in Mn3.1Sn0.9. This noncollinear antiferromagnetic alloy exhibits a Neel temperature of 325 K. Upon cooling from 325 K, a magnetic phase transition from noncollinear antiferromagnetism to ferromagnetism occurs at 168 K due to the tilting of magnetization towards c axis. Above this temperature, anomalous Hall resistivity ranged from 0.6 to 1.3 mu omega cm has been observed in noncollinear antiferromagnetic state. Below this temperature, a topological Hall effect (THE) starts to appear due to the non-vanishing scalar spin chirality arising from the noncoplanar spin structure. Further decreasing temperature to 132 K, another magnetic transition happens, resulting in the coexistence of ferromagnetism and antiferromagnetism, so that a Hall plateau with large hysteresis below 70 K is yielded. A hysteresis as high as similar to 80 kOe is obtained in rho(xy)-H at 15 K. However, the Hall plateau disappears and only anomalous Hall effect (AHE) persists when further decreasing the temperature to 5 K. The present study provides a picture of diverse magneto-transport properties correlated to the variable spin structures driven by magnetic phase transitions.

Keyword ：

topological Hall effect anomalous Hall effect non-collinear antiferromagnet

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Microrobots capable of performing minimally invasive surgery, targeted drug delivery, and manipulation of micro-objects have shown great potentials in multiple application areas. However, microrobots assembled by nanoparticles with stable configuration and good performance on closed-loop control are still to be further studied. In this paper, ferromagnetic nanoparticles are used as experimental materials, rather than paramagnetic nanoparticles that require complex synthesis processes, and the advantage is demonstrated, for example, high pattern stability. The locomotion velocity as a function of the magnetic field frequency is modeled, analyzed and verified by experiment. Moreover, a path following experiment based on the arbitrary planar path following algorithm is performed. The nanoparticle microrobots are of great significance for biomedical applications. In the future works, experiments in bio-fluids, multimodal locomotion, and targeted drug delivery tasks will be investigated. © 2021 IEEE.

Keyword ：

Medical applications Synthesis (chemical) Targeted drug delivery Controlled drug delivery Closed loop control systems Microrobots Ferromagnetic materials Nanoparticles Ferromagnetism

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Electrides in a two-dimensional (2D) scale, especially those that capture inherent magnetism and have low work functions, have shown great application prospects in nanoscale spintronic devices and electronic emitters. However, searching for ideal 2D magnetic electrides is still a great challenge. Herein, based on first-principles calculations, we demonstrate that 2D CaCl is strippable from the heterostructure of experimental CaCl/graphene and reveal that the freestanding 2D CaCl has a novel electride phase. In this material, sufficient electrons are trapped in the lattice voids and act as anions within the positive crystalline framework, following the electride form of [CaCl](+)center dot e(-). Due to the unique electron behaviour of electrides, the 2D [CaCl](+)center dot e(-) possesses a series of interesting physical phenomena: (1) the electride [CaCl](+)center dot e(-) exhibits room-temperature ferromagnetism, where the magnetic moment originates from the excess electrons with an s-like orbital feature rather than the atomic orbital ones, which is drastically different from traditional 2D ferromagnets; (2) the electride [CaCl](+)center dot e(-) shows magnetic metal characteristics, and by doping with halogen elements, its electronic structure can be effectively regulated; (3) most remarkably, the FM electride [CaCl](+)center dot e(-) shows an extremely low work function (2.65 eV). This value is the lowest among the electrides in 2D materials reported so far. Besides, the dimension of excess electrons can be effectively regulated by controlling the temperature. This work provides an excellent candidate to investigate 2D magnetic electrides and their associated applications.

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Since the discovery of intrinsic ferromagnetism in atomically thin Cr(2)Gr(2)Te(6) and CrI3 in 2017, research on two-dimensional (2D) magnetic materials has become a highlighted topic. Based on 2D magnetic materials and their heterostructures, exotic physical phenomena at the atomically thin limit have been discovered, such as the quantum anomalous Hall effect, magneto-electric multiferroics, and magnon valleytronics. Furthermore, magnetism in these ultrathin magnets can be effectively controlled by external perturbations, such as electric field, strain, doping, chemical functionalization, and stacking engineering. These attributes make 2D magnets ideal platforms for fundamental research and promising candidates for various spintronic applications. This review aims at providing an overview of the structures, properties, and external controls of 2D magnets, as well as the challenges and potential opportunities in this field.

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