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Transition metal and rare earth intermetallics have been a fertile playground for the study of various quantum states. In this work, we report detailed magnetic studies on SmMn2Ge2, an anisotropic itinerant magnet with multiple magnetic phases. We investigated the critical behavior of the ferromagnetic phase transition by the modified Arrott plot (MAP) and Kouvel-Fisher (KF) method. The critical temperature T C is determined to be around 342.7 K with critical exponents of β = 0.417 and γ = 1.122, and the interaction function is found to be J(r)~r -4.68, suggesting the coexistence of long-range and short-range magnetic interactions. Our results contribute to the understanding of complex magnetism in SmMn2Ge2, which may provide fundamental guidance in future spintronic applications.

Charge neutrality and their expected itinerant nature makes excitons potential transmitters of information. However, exciton mobility remains inaccessible to traditional optical experiments that only create and detect excitons with negligible momentum. Here, using angle-resolved photoemission spectroscopy, we detect dispersing excitons in the quasi-one-dimensional metallic trichalcogenide, TaSe3. The low density of conduction electrons and the low dimensionality in TaSe3 combined with a polaronic renormalization of the conduction band and the poorly screened interaction between these polarons and photo-induced valence holes leads to various excitonic bound states that we interpret as intrachain and interchain excitons, and possibly trions. The thresholds for the formation of a photo-hole together with an exciton appear as side valence bands with dispersions nearly parallel to the main valence band, but shifted to lower excitation energies. The energy separation between side and main valence bands can be controlled by surface doping, enabling the tuning of certain exciton properties., 18 pages, 4 figures, modified version. Nat. Mater. (2022)

We report differential phase contrast scanning transmission electron microscopy (TEM) of nanoscale magnetic objects in Kagome ferromagnet Fe3Sn2 nanostructures. This technique can directly detect the deflection angle of a focused electron beam, thus allowing clear identification of the real magnetic structures of two magnetic objects including three-ring and complex arch-shaped vortices in Fe3Sn2 by Lorentz-TEM imaging. Numerical calculations based on real material-specific parameters well reproduced the experimental results, showing that the magnetic objects can be attributed to integral magnetizations of two types of complex three-dimensional (3D) magnetic bubbles with depth-modulated spin twisting. Magnetic configurations obtained using the high-resolution TEM are generally considered as two-dimensional (2D) magnetic objects previously. Our results imply the importance of the integral magnetizations of underestimated 3D magnetic structures in 2D TEM magnetic characterizations.

The effects of typical acid and alkaline aroma additives on the release characteristics of aroma components from reconstituted tobacco were studied. In this study, the pyrolysis of reconstituted tobacco samples loaded with different aroma components was carried out, and the aroma components in the smoke were analyzed by the GC-MS. The results showed that adding a certain amount of acid aroma components in reconstituted tobacco could promote the release of aroma components in smoke. However, excessive acid aroma additives could inhibit the Maillard reaction to decrease the formation of additional aroma components during pyrolysis. The addition of ethanol in reconstituted tobacco could promote the release of olefin and acid aroma components in smoke. Alkaline aroma additives (sodium bicarbonate and potassium carbonate) could promote the release of all kinds of aroma components in smoke, because potassium and sodium ions could catalyze the pyrolysis of tobacco, which was preferred to generate aroma components. According to these results, the best promoting effect of the aroma components released in smoke was performed by adding 0.078 wt% of potassium carbonate and 0.01 wt% of citric acid in reconstituted tobacco.

Magnetic skyrmions are localized particle-like nontrivial swirls that are promising in building high-performance topological spintronic devices. The read-out functions in skyrmionic devices require the translation of magnetic skyrmions to electrical signals. Here, we report combined real-space magnetic imaging and anisotropic magnetoresistance studies on dipolar skyrmions. A single skyrmion chain and single skyrmion are observed using Lorentz transmission electron microscopy imaging. Meanwhile, the field, helicity, and skyrmion count dependence of anisotropic magnetoresistance of the Fe3Sn2 nanostructures are obtained simultaneously. Our results demonstrate that the anisotropic magnetoresistance of skyrmions is independent of the helicity and proportional to the skyrmion count. Our work could promote read-out operations in skyrmion-based spintronic devices.

Magnetic van der Waals (vdW) materials are poised to enable all-electrical control of magnetism in the two-dimensional limit. However, tuning the magnetic ground state in vdW itinerant ferromagnets by voltage-induced charge doping remains a significant challenge, due to the extremely large carrier densities in these materials. Here, by cleaving the vdW itinerant ferromagnet Fe

We studied effects of tilted magnetocrystalline anisotropy on the magnetic domains in a bubble-hosting magnet ${\mathrm{Fe}}_{3}{\mathrm{Sn}}_{2}$. With increasing the in-plane uniaxial magnetocrystalline anisotropy, the magnetic ground state in ${\mathrm{Fe}}_{3}{\mathrm{Sn}}_{2}$ thin plates changes from disordered stripe domains to stripe domains with preferred orientation. Through transport of intensity equation analysis, we further characterized the transition from skyrmion bubbles to biskyrmionlike configurations with increase in the tilted in-plane magnetocrystalline anisotropy when an out-of-plane magnetic field was applied. In addition, differential phase contrast scanning transmission electron microscopy (DPC-STEM) observations and micromagnetic simulations were carried out to confirm that the biskyrmionlike configurations were type-II bubbles. We show that, in addition tilting a magnetic field to induce misalignment between the magnetic field and the easy magnetization axis, tilting the uniaxial magnetic anisotropy can also be used to stabilize type-II bubbles. Our results also indicate DPC-STEM can help to distinguish between type-II bubbles and biskyrmions.

Zr-Te compounds are an ideal platform to investigate novel electrical transport properties. Here we report the Kondo effect in single-crystalline ${\mathrm{ZrTe}}_{2}$. When $Tl8$ K, ${\mathrm{ZrTe}}_{2}$ exhibits a $\mathrm{log}T$ dependence of resistivity, which may derive from three different mechanisms, including electron-electron interaction, weak localization, and Kondo effect. By measuring transport properties with magnetic field along different directions, the former two mechanisms were excluded. Isotropic negative magnetoresistance was extracted by subtracting different quadratic background signals caused by Lorentz force, which reveals the existence of a weak Kondo effect in this material.

Topological magnetic charge Q is a fundamental parameter that describes the magnetic domains and determines their intriguing electromagnetic properties. The ability to switch Q in a controlled way by electrical methods allows for flexible manipulation of electromagnetic behavior in future spintronic devices. Here we report the room-temperature current-controlled topological magnetic transformations between Q = -1 skyrmions and Q = 0 stripes or type-II bubbles in a kagome crystal Fe$_3$Sn$_2$. We show that the reproducible and reversible skyrmion-bubble and skyrmion-stripe transformations can be achieved by tuning the density of nanosecond pulsed current of the order of ~10$^{10}$ A$^{-2}$. Further numerical simulations suggest that spin-transfer torque combined with Joule thermal heating effects determine the current-induced topological magnetic transformations.

The topological nodal-line semimetal (TNLS) $\mathrm{ZrSi}M$ $(M=\mathrm{S}, \mathrm{Se}, \mathrm{Te})$ is a promising platform to study the TNLS phase by tuning chalcogens. In this work, we study the evolution of the Fermi surface (FS) by tuning the Se/Te ratio in ${\mathrm{ZrSiSe}}_{1\ensuremath{-}x}{\mathrm{Te}}_{x}$ compounds. Transport properties and magnetometry results present signatures of Fermi surface topology change by the sudden changes in symmetry and carrier densities, as well as singularity of FSs at the critical chemical potentials. A $2\frac{1}{2}$-order Lifshitz transition occurs when 0.20 $\ensuremath{\le}\phantom{\rule{4pt}{0ex}}x\phantom{\rule{4pt}{0ex}}\ensuremath{\le}$ 0.33. Another $3\frac{1}{2}$-order electron topological transition is revealed by a large diamagnetic anomaly of susceptibility at $x\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}$ 0.80. In combination with first-principles calculations, this study reveals the vital roles of spin-orbit coupling, charge transfer, and shifts of the chemical potential in the evolution of FSs in this system. Our results demonstrate how the FSs evolve in ${\mathrm{ZrSiSe}}_{1\ensuremath{-}x}{\mathrm{Te}}_{x}$ compounds, providing fundamental clues for designing topological state switchable devices.

Magnetic van der Waals (vdW) materials, including ferromagnets (FM) and antiferromagnets (AFM), have given access to the investigation of magnetism in two-dimensional (2D) limit and attracted broad interests recently. However, most of them are semiconducting or insulating and the vdW itinerant magnets, especially vdW itinerant AFM, are very rare. Here, we studied the anomalous Hall effect of a vdW itinerant magnet Fe$_5$GeTe$_2$ (F5GT) with various thicknesses down to 6.8 nm (two unit cells). Despite the robust ferromagnetic ground state in thin-layer F5GT, however, we show that the electron doping implemented by a protonic gate can eventually induce a magnetic phase transition from FM to AFM. Realization of an antiferromagnetic phase in F5GT highlights its promising applications in high-temperature antiferromagnetic vdW devices and heterostructures., 27 pages

Transition metal dichalcogenides with nontrivial band structures exhibit various fascinating physical properties and have sparked intensively research interest. Here, we performed systematic magnetotransport measurements on mechanical exfoliation prepared ZrTe2 nanoplates. We revealed that the negative longitudinal magnetoresistivity observed at high field region in the presence of parallel electric and magnetic fields could stem from the conductivity fluctuations due to the excess Zr in the nanoplates. In addition, the parametric plot, the planar Hall resistivity as function of the in-plane anisotropic magnetoresistivity, has an ellipse-shaped pattern with shifted orbital center, which further strengthen the evidence for the conductivity fluctuations. Our work provides some useful insights into transport phenomena in topological materials., Comment: 23 pages, 5 figures

Charge neutrality and their expected itinerant nature makes excitons potential transmitters of information. However, exciton mobility remains inaccessible to traditional optical experiments that only create and detect excitons with negligible momentum. Here, using angle-resolved photoemission spectroscopy, we detect dispersing excitons in the quasi-one-dimensional metallic trichalcogenide, TaSe

We report a vortex-like magnetic configuration in uniaxial ferromagnet Fe

The weak interlayer coupling in van der Waals (vdW) magnets has confined their application to two dimensional (2D) spintronic devices. Here, we demonstrate that the interlayer coupling in a vdW magnet Fe_{3}GeTe_{2} (FGT) can be largely modulated by a protonic gate. With the increase of the protons intercalated among vdW layers, interlayer magnetic coupling increases. Because of the existence of antiferromagnetic layers in FGT nanoflakes, the increasing interlayer magnetic coupling induces exchange bias in protonated FGT nanoflakes. Most strikingly, a rarely seen zero-field cooled (ZFC) exchange bias with very large values (maximally up to 1.2 kOe) has been observed when higher positive voltages (V_{g}≥4.36 V) are applied to the protonic gate, which clearly demonstrates that a strong interlayer coupling is realized by proton intercalation. Such strong interlayer coupling will enable a wider range of applications for vdW magnets.

We report differential phase contrast scanning transmission electron microscopy (TEM) of nanoscale magnetic objects in Kagome ferromagnet Fe3Sn2 nanostructures. This technique can directly detect the deflection angle of a focused electron beam, thus allowing clear identification of the real magnetic structures of two magnetic objects including three-ring and complex arch-shaped vortices in Fe3Sn2 by Lorentz-TEM imaging. Numerical calculations based on real material-specific parameters well reproduced the experimental results, showing that the magnetic objects can be attributed to integral magnetizations of two types of complex three-dimensional (3D) magnetic bubbles with depth-modulated spin twisting. Magnetic configurations obtained using the high-resolution TEM are generally considered as two-dimensional (2D) magnetic objects previously. Our results imply the importance of the integral magnetizations of underestimated 3D magnetic structures in 2D TEM magnetic characterizations., We demonstrate three-dimensional magnetic bubbles for the first time from the view of integral magnetizations, which clarify the physics behind complex multi-ring and arc-shaped vortices obtained from two-dimensional transmission electron microscopy magnetic imaging.

The weak interlayer coupling in van der Waals (vdW) magnets has confined their application to two dimensional (2D) spintronic devices. Here, we demonstrate that the interlayer coupling in a vdW magnet Fe_{3}GeTe_{2} (FGT) can be largely modulated by a protonic gate. With the increase of the protons intercalated among vdW layers, interlayer magnetic coupling increases. Because of the existence of antiferromagnetic layers in FGT nanoflakes, the increasing interlayer magnetic coupling induces exchange bias in protonated FGT nanoflakes. Most strikingly, a rarely seen zero-field cooled (ZFC) exchange bias with very large values (maximally up to 1.2 kOe) has been observed when higher positive voltages (V_{g}≥4.36 V) are applied to the protonic gate, which clearly demonstrates that a strong interlayer coupling is realized by proton intercalation. Such strong interlayer coupling will enable a wider range of applications for vdW magnets.

Understanding the mechanisms for forming skyrmionic spin configurations at room temperature is essential for exploring the applicable spintronics devices based on topological spin textures. In this work, the anisotropic magnetic properties and critical behavior are investigated in noncollinear itinerant magnet PrMn2Ge2. The strongly anisotropic magnetic interactions and magnetic field and temperature induced antiferromagnetic to ferromagnetic transition are observed. The critical behavior of high temperature ferromagnetic transition at 331 K was analyzed, and the critical exponents β = 0.335, γ = 0.878, and δ = 3.617 are extracted by the modified Arrott plot method, which lie between the values of long-range mean-field and short-range three-dimensional theories, demonstrating that PrMn2Ge2 possesses multiple magnetic interactions. This is also confirmed by the moderated interaction function, which is decay as J( r) ∼ [Formula: see text]. Therefore, the competition of multiple magnetic interactions in PrMn2Ge2 is analogous to what has been observed in GdRu2Si2 and could be the origin of skyrmionic bubbles observed at room temperature.

The vapor-/solid-phase interactions are the inevitable phenomenon in biomass pyrolysis process, which significantly affects the formation of heavy components (molecular weight > 200 Da) in bio-oil (HCO). In this study, to deeply understand the mechanism of the formation of HCO during biomass pyrolysis, the effects of the vapor-/solid-phase interactions among cellulose, hemicellulose, and lignin (biomass three components) on the formation of HCO during pyrolysis were studied in a fixed-bed reactor system. The HCO were analyzed by the FT-ICR MS spectrometer and the UV-F spectrometer. The results showed that the vapor-phase interactions mainly promoted the formation of heavy phenolic compounds at a slow heating rate, and the total content of HCO was increased. The vapor-phase interactions decreased the total content and the O content of HCO obviously at a fast heating rate; meanwhile, the highly reactive compounds (e.g., furans, acids, and ketones) generated from the pyrolysis of cellulose and hemicellulose could interact with the phenol monomers. Thus the phenolic compounds were transformed into large aromatic compounds via the vapor-phase interactions. The solid-phase interactions facilitated the transformation of O-containing structures of the HCO into the char via cross-condensation reaction, decreasing the yield of HCO, especially the phenolic compounds and the saccharides.

Interstitial iron ( Fe i ) has strong influence on physical properties of Fe 1 + x Sb (0.08 ⩽ x ⩽ 0.38) compounds. We synthesized Fe 1.08 Sb single crystals with Fe i content close to the lower limit of solution area and investigated its transport and magnetic properties. The ac susceptibility and field dependence of magnetization measurements demonstrate that the transition at ∼9 K is a spin glass transition. By analyzing temperature dependence of susceptibility ( χ vs T) and resistivity (d2 ρ /dT2 vs T) results, we found a change of scattering in transport properties caused by the ordering of Fe i moments in this compound. In addition, the Hall resistivity results reveal that the hole-type carrier is dominant and the topological Hall effect induced by spin chirality is negligible in Fe 1.08 Sb.

The physical properties of itinerant ferromagnet [Formula: see text]-Co

Electrocatalytic hydrogenation is a potential means to upgrade bio-oil under mild working conditions. Here we report the formation of a carbonaceous solid (coke) on the surface of the electrode and its impacts during the electrochemical upgrading of bio-oil. The electrolytic experiments were conducted under the condition of 200 mA cm−2, 25 °C, and ambient pressure. As the electrolytic experiments progressed, the aromatic structures in the bio-oil were decreasing, while the radicals were increasing in their types and concentrations. The aromatic structures in the bio-oil were polymerized to form coke with heteroatom-containing radicals. The coke-covered electrode would enhance the oxidation process and inhibit the transformation of the aromatic structures in bio-oil. Moreover, the heteroatom-containing radicals contained in the initial coke would further enhance the coke formation. Last, an initial strategy was reported to remove the coke deposited on the surface of the electrode during the electrochemical upgrading of bio-oil.

Recently discovered massive Dirac fermions and room temperature skyrmions in the ferromagnetic kagome metal Fe3Sn2 have attracted extensive attention due to the potential applications in topological and spintronic devices. Because of its centrosymmetric lattice, the topological spin texture in Fe3Sn2 arises primarily from the competition between anisotropy and exchange interaction. In this Letter, we have identified the spin-reorientation at around 80 K by the magnetization and AC-susceptibility measurements. The evolution of the anisotropy is revealed by neutron powder diffraction data from 18 to 700 K, where the “breathing”-like kagome structure evolves into an ideal kagome lattice at higher temperature. Meanwhile, the deviation between the experimental and calculated results on heat capacity at high temperature and the softening of optical phonon modes in Raman spectra suggest the presence of anharmonic phonons in Fe3Sn2, which is responsible for the degeneracy of lattice thermal conductivity at high temperature. Our study indicates that Fe3Sn2 possesses a promising future in the design and development of topological, spintronic as well as thermoelectric devices.

Magnetic k π -skyrmions are rotationally symmetric vortex-like solitons, whose magnetization rotates by an angle of k π from its center to outermost boundary. Here, we report k π -skyrmions (k = 2, 3, and 4) and their field-driven magnetic evolutions in centrosymmetric uniaxial ferromagnetic Fe3Sn2 nanodisks. We show that zero-field non-axisymmetric k π -skyrmions turn to be axisymmetric after applying an out-of-plane field. The collapses of ( k + 1 ) π -skyrmions to k π -skyrmions induced by external field are also experimentally identified. Furthermore, numerical simulations well reproduce experimental magnetization mapping of k π -skyrmions and further demonstrate their three-dimensional magnetic structures.

Magnetic bubbles are cylinder domains found in a wide variety of uniaxial ferromagnets. They are categorized into two types based on the rotational sense of their domain walls. These two types of bubbles have the potential to be binary states in a skyrmion-bubble-based magnetic memory. Experimental realization of a single bubble along with single bubble transformations in nanostructures is important for single bit operations in such a memory but has not yet been demonstrated. In this study, effects of geometrical confinement on stabilization and transformation of magnetic bubbles in Fe3Sn2 disks were explored. We observed magnetic bubble cluster states with a tunable bubble number based on the disk size and tilted field angle. By tracking the size dependence of the bubble number, we further demonstrate how both types of single bubbles can be realized and transformed into each other in a controlled manner without bubble number variation.

For some 3d transition-metal monopnictides, their physical properties are strongly affected by interstitial 3d transition-metal atoms, such as Fe1+δSb, in which the electrical transport, magnetic properties and carrier concentrations have strong dependence on the composition of interstitial Fe (Shiomi et al. Phys. Rev. Lett. 108(5), 056601 2012), Therefore, it is important to study the influence of interstitial Co on the physical properties of Co1+δSb. Here, the magnetic and transport properties have been studied on Co1.05Sb single crystals. The magnetic and electrical transport measurements reveal that stoichiometric CoSb is a nonmagnetic metal. The interstitial Co in this compound exhibits a paramagnetic behaviour and weak antiferromagetic correlations. However, it has no effect on transport properties. A very low magnetoresistance (≤ 0.2%) was observed under the magnetic field up to 14 T, which suggests that Co1+δSb could be a potential material of electronic devices for the application at a high magnetic field.

The electronic structures of rubrene films deposited on CH3NH3PbI3 perovskite have been investigated using in situ ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS). It was found that rubrene molecules interacted weakly with the perovskite substrate. Due to charge redistribution at their interface, a downward ‘band bending’-like energy shift of ∼0.3 eV and an upward band bending of ∼0.1 eV were identified at the upper rubrene side and the CH3NH3PbI3 substrate side, respectively. After the energy level alignment was established at the rubrene/CH3NH3PbI3 interface, its highest occupied molecular orbital (HOMO)–valence band maximum (VBM) offset was found to be as low as ∼0.1 eV favoring the hole extraction with its lowest unoccupied molecular orbital (LUMO)–conduction band minimum (CBM) offset as large as ∼1.4 eV effectively blocking the undesired electron transfer from perovskite to rubrene. As a demonstration, simple inverted planar solar cell devices incorporating rubrene and rubrene/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hole transport layers (HTLs) were fabricated in this work and yielded a champion power conversion efficiency of 8.76% and 13.52%, respectively. Thus, the present work suggests that a rubrene thin film could serve as a promising hole transport layer for efficient perovskite-based solar cells.

Nontrivial spin configurations tend to bring about novel transport properties in magnetic materials. We report the magnetic anisotropy and topological Hall effect in trigonal ${\mathrm{Cr}}_{5}{\mathrm{Te}}_{8}$ single crystals. Below the magnetic transition temperature, the spins are canted ferromagnetic aligned along $c$ axis with antiferromagnetic components in $ab$ plane. This peculiar magnetic structure gives rise to the anisotropic anomalous Hall effect (AHE) in ${\mathrm{Cr}}_{5}{\mathrm{Te}}_{8}$. When the current flows along the $ab$ plane, ${\mathrm{Cr}}_{5}{\mathrm{Te}}_{8}$ exhibits a conventional AHE depicted by skew scattering mechanism. On the other hand, the topological Hall effect appears with current along $c$ axis, which stems from the noncoplanar spin configuration with scalar spin chirality during the spin flop process.

Fundamental understanding on the spin transport properties of semiconducting organic-inorganic hybrid perovskites (OIHP) is of great importance for advancing their applications for spin-optoelectronic devices. Herein, the study of spin-pumping induced inverse spin Hall effect in Ni80Fe20(Py)/CH3NH3PbCl3-xIx/Pt trilayers with different OIHP spacer thicknesses concludes the spin diffusion length in CH3NH3PbCl3-xIx as large as 61 ± 7 nm at room temperature. In addition, spin-valves with a structure of Ni80Fe20(Py)/CH3NH3PbCl3-xIx/AlOx/Co was fabricated as well. Using a ∼160 nm-thick CH3NH3PbCl3-xIx spacer, the present spin valve exhibits a positive magnetoresistance (MR) of 0.57% at 10 K. Thus, the present spin related results demonstrate that electrical spin-polarized carrier injection, transport, and detection, which are essential in spintronic devices, can be successfully established in OIHP films. The outstanding spin transport in the present CH3NH3PbCl3-xIx should be owing to its highly out-of-plane oriented crystalline texture and Rashba spin splitting at domain boundaries between crystallographic orientations. These results demonstrate OIHP as very attractive materials for spintronics.

Magnetic memories based on localized magnetic objects with high performance are potentially applicable to future memory devices. In such devices, binary data bits “1” and “0” are suggested to be represented by skyrmions or skyrmion bubbles and ferromagnetic gaps, respectively. However, thermal fluctuations and interactions between skyrmions can induce interruptions in the stored data, and additional pinning sites must be fabricated. Here, we suggest that a pinning site-free magnetic memory, called skyrmion-bubble-based memory, can be realized in bubble-hosting magnets. In skyrmion-bubble-based memory, topologically trivial bubbles are used to replace ferromagnetic gaps to represent the other binary bits. A data bitstream can, thus, be represented by a skyrmion-bubble chain, and interactions between two neighbored magnetic objects can naturally suppress undesired motion of data bits. Further, a single skyrmion-bubble chain representing a data bitstream is realized experimentally in a typical bubble-hosting material, Fe3Sn2 nanostripe.