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Inverse spinel oxide NiCo2O4 is an excellent prototype to explore complex energy landscapes among exchange interactions, crystal field effects, and chemical/lattice disorders. In this work, periodi...

为满足实际应用, 自旋电子学器件需要自旋在特定方向发生自发取向, 但这通常是难以控制的. 在本文中, 我们观察了沿b轴的单晶Gd0.75La0.25FeO3在室温下伴随着弱铁磁(wFM)成分的反铁磁(AFM)磁有序. 与普通的AFM材料不同, 这里的wFM磁矩是离散的, 类似于二维量子阱, 可以通过一个小磁场在两个状态之间切换. 量子阱中的势垒使得矫顽力在50–350 K的宽温度范围内保持稳定, 并在17 K时产生独特的自旋翻转现象. 此外, 在RFeO3(R=稀土)中, 稀土和铁的次晶格之间普遍存在着一种AFM耦合. 而在Gd0.75La0.25-FeO3中, Gd与Fe次晶格之间的AFM耦合被破坏, 使得Gd被诱导出的磁矩与Fe磁矩方向不再相反, 而是表现出与Fe磁矩方向相同的诱导磁矩. 由于在GdFeO3或LaFeO3中不存在自旋翻转, 因此AFM耦合的破坏也被认为是材料表现出一种独特的自旋翻转现象的主要原因. 以上性质使得Gd0.75La0.25FeO3在信息存储方面具有更优良的可控性.

Controlling the phases and structure of nanostructured rare-earth-based permanent magnets is essential to develop magnets with high performance in clean energy technologies. Importantly, simultaneously controlling the texture and morphology of nano-grains can lead to both high coercivity and high maximum energy product in the nanostructured magnets. Here, we demonstrated the use of electron-beam exposure (EBE) as a rapid heating technique to control the crystallization of the Pr-Fe-B magnet. Due to the effect of the extremely high heating rate, EBE can be adapted to control the phase, grain size, and morphology of the amorphous precursor as well as the texture of Pr-Fe-B nano-grains. A quasi-texture nanostructure with optimal magnetic exchange interactions is thus achieved, leading to a record-high coercivity of 29.1 kOe at room temperature. We further applied the Landau model and Coble-Creep model to explain the positive impact of the EBE on the crystallization and microstructure of the Pr-Fe-B magnet.

Magnetic properties of single perovskite-structure epitaxial film are reported to have layered distribution recently. However, the different responses of spin configurations in individual layers to the variations of temperature and strain state, especially the subtle response of layered film due to structural phase transformation of SrTiO3 (STO) substrate around 105 K, have not been revealed completely. Drastic drop and concomitant abnormal increase of remnant magnetic moments (REM) and coercivity of low-doped La1-xSrxMnO3 (x = 0.175) /SrTiO3 film were observed around 105 K only in the in-plane direction, and layered magnetic structures were further inferred based on investigation of microstructure, strain distribution and chemical inhomogeneity. Abnormal change of magnetic properties around 105 K was discussed by a three-layer model, in which softer ferromagnetic layer was supposed to form in the middle layer of strain-induced layered structure, and the spin configuration of middle layer underwent non-synchronous transformation relative to other parts of the film, which may be attributed to the change of in-plane strain inside the film around 105 K. Our work reveals the variation of individual magnetic layers with the increase of temperature through utilizing the remnant magnetic field in measuring system, and the abrupt reversal of spin configurations at the intermediate layer can also serve the design of novel spintronics devices in the future.

In this work, we report the tuning effect of the Si substitution on the magnetic and high frequency electromagnetic properties of R2Fe17 compounds and their paraffin composites. It is found that the introduction of Si can remarkably improve the magnetic and electromagnetic properties of the R2Fe17 compounds, making the R2Fe17–xSix-paraffin composites excellent microwave absorption materials (MAMs). By introducing the Si element, their saturation magnetizations decrease slightly, while much higher Curie temperatures are obtained. Furthermore, better impedance match is reached due to the decrease of the high-frequency permittivity e′ by about 40%–50%, which finally enhances the performance of the microwave absorption. The peak frequency (fRL) of the reflection loss (RL) curve moves toward high frequency domain and the qualified bandwidth (QB, RL ≤ −10 dB) increases remarkably. The maximum QB of 3.3 GHz (12.0–15.3 GHz) is obtained for the Sm1.5Y0.5Fe15Si2-paraffin composite (d = 1.0 mm) and the maximum RL of −53.6 dB is achieved for Nd2Fe15Si2-paraffin composite (d = 2.2 mm), both surpassing most of the reported MAMs. Additionally, a distinguished dielectric microwave absorption peak is observed, which further increases the QB in these composites.

The crystal structures, magnetic properties and electronic structures of pseudo-binary compounds Pr5SixGe3-x were investigated. With the increase of the Ge content, structure of Pr5SixGe3-x gradually changes from the tetragonal Cr5B3-type to the hexagonal Mn5Si3-type. For the compounds with the tetragonal structure, the unit cell volumes as well as the magneto-crystalline anisotropy energy (MAE) increase with the Ge content, leading to the diminishing of the magnetization and the maximum magnetic entropy changes -ΔSM. As compared to the binary compound Pr5Si3, the intermetallic compounds with Ge doping show broader working temperature span and considerably large relative cooling power (213.9, and 184.8 J kg−1 at ΔH = 50 kOe for Pr5Si2.5Ge0.5 and Pr5Si2Ge, respectively). For the hexagonal compound Pr5Ge3, a large MAE and an easy magnetization direction close to c axis (polar angle θ ∼7°) were calculated, which is related to the macroscopic magnetic transition behavior at low temperature.

Multiferroic materials have the potential to be applied in novel magnetoelectric devices, for example, high-density non-volatile storage devices. During the last decades, research on multiferroic materials was focused on three-dimensional (3D) materials. However, 3D materials suffer from dangling bonds and quantum tunneling in nano-scale thin films. Two-dimensional (2D) materials might provide an elegant solution to these problems, and thus are highly in demand. Using first-principles calculations, we predicted ferromagnetism and electric-field-driving ferroelectricity in the monolayer and even in the few-layers of CuCrP2S6. Although the total energy of the ferroelectric phase of the monolayer is higher than that of the antiferroelectric phase, the ferroelectric phases can be realized by applying a large electric field. Besides the degrees of freedom in the common multiferroic materials, the valley degree of freedom is also polarized, according to our calculations. The spins, electric dipoles and valleys are coupled with each other as shown in the computational results. In our experiment, we observed the out-of-plane ferroelectricity in few-layer CuCrP2S6 (approximately 13 nm thick) at room temperature. 2D ferromagnetism of few-layers is inferred from the magnetic hysteresis loops of the massively stacked nanosheets at 10 K. The experimental observations support our calculations very well. Our findings may provide a series of 2D materials for further device applications.

As municipal solid waste severely threatens human health and the ecological environment, since 2019, China has started to fully practice MSW sorting in all prefecture-level cities. In this paper, we apply the event study and difference-in-difference methods to investigate how China’s green policy of promoting MSW sorting influences listed waste sorting companies from the perspective of investors’ short-term and long-term reactions. This paper finds that investors are not sensitive to the introduction of MSW sorting in the short term, the new environmental policy does not relieve the financing constraints of related enterprises in the long run, and the financing constraints of private enterprises are stricter than those of state-owned enterprises. These findings indicate that China’s current encouragement of garbage sorting is not efficient enough as it has not brought benefits to the waste classification industry yet. More measures need to be taken to eliminate uncertainties in urban waste sorting. Our paper enriches the research on China’s waste sorting practices and provides new evidence of the effects of environmental policy on related firms from the perspective of green industry.

Ce2Fe14B compound has a great potential to serve as a novel permanent magnet alternative thanks to the abundant and inexpensive rare-earth element (cerium), while its low magnetocrystalline anisotropy and energy product severely restrict its applications. In this work, a novel strategy combining melt-spinning and electron-beam exposure (EBE) aiming for fabricating high-performance Ce-Fe-B magnetic materials is reported to solve the above-mentioned problem. Remarkably, this strategy facilitates developing a suitable grain boundary configuration without using any additional heavy rare-earth element. Under the optimal EBE condition, the maximum energy product ((BH)max) of pure Ce-Fe-B alloy is 6.5 MGOe, about four times higher than that obtained after conventional rapid thermal processing method for the same precursor. The enhanced intergranular magnetostatic coupling effect in the EBE sample is validated by mapping the first-order-reversal-curve (FORC) diagrams. The in-situ observation of magnetic domain wall motion for Ce-Fe-B alloy using Lorentz transmission electron microscopy reveals that the boundary layers are very effective in pinning the motion of domain walls, leading to the increased coercivity under EBE, and this pinning effect is further verified by micromagnetic simulations. Our results suggest that CeFeB materials using EBE could be a promising candidate after further processing, which could fill the performance “gap” between hexaferrite and Nd-Fe-B-based magnets.

In this study alloys with stoichiometry of R2Fe17 and R10Fe90-xSix (x = 0, 10, 15, 20) (R = Y, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Er) have been prepared. Structural transition from the ordered rhombohedral (OR) Th2Zn17-type structure and the ordered hexagonal (OH) Th2Ni17-type structure to their disordered structures (DR and DH) has been observed according to the XRD patterns. The lattice parameters were obtained by Rietveld analysis and based on the changing characteristic of the parameters, these samples are divided into two categories: alloys with R = Ce, Pr, Nd, Sm and alloys with R = Y, Gd, Td, Dy, Ho, Er. The lattice parameters of the two categories show different changing behavior. For example, from R2Fe17 to R10Fe90, the lattice parameters a decrease and c increase for the latter category, whereas for the former the lattice parameters a and c nearly have no change. In addition, increase of the ratio c/a has been found with increasing Fe or Si content, indicating the introduction of extra Fe dumbbells into the crystal cells, forming the DR or DH intermetallic compounds of R2-y(Fe,Si)17+2y. The obtained samples with disordered structure have shown better stability than the TbCu7-type metastable materials and the higher Fe concentration gives promise of higher magnetization. The mixed-rare-earth effect has also been studied in the (Ce,R)10Fe75Si15 alloys and transition between the DR and DH structures has been realized by changing the mixed R-type or adjusting the Ce/R ratio. As for the magnetic properties, the Curie temperatures are increased remarkably by the introduction of Si and the saturation magnetizations of R10Fe90-xSix are often higher than that of the R2Fe17 alloys.

The compromise between intensity and resolution is the core issue for the powder neutron diffraction techniques. An investigation of the optimum configuration of a neutron instrument is necessary to meet the requirement for both the intensity and resolution before the final construction. In this paper, the performance of the high-intensity powder neutron diffractometer (HIPD) at China Advanced Research Reactor has been studied by Monte Carlo simulation and convolution methods. The virtual detector Monitor-nD with super fine recording elements was used to record the diffraction patterns of the simulated HIPD. In order to introduce the spatial resolution effect of the detector in the diffraction pattern, the convolution method was adopted. The diffraction peaks from the diffraction patterns were then used to calculate the minimum interplanar spacing difference $\Delta d$ that the HIPD can distinguish. It is obtained that the minimum resolution of the HIPD is $2.08 \times 10^{-3}$ ( $\Delta d/d$ ) for the current design. The resolution of the HIPD calculated above is consistent with the resolution actually measured according to the Ni sample diffraction experiment. This indicates that the above simulation method has high reliability. Finally, a movable $20^{\prime }$ Soller collimator and sample cans with 3 and 6 mm diameters are recommended to be used to optimize the ND experiment. After installing the $20^{\prime }$ Soller collimator, the minimum resolution can be $1.88 \times 10^{-3}$ ( $\Delta d/d$ ). The diffraction intensity of the 6-mm-diameter sample will be almost 3 times higher than that of the 3-mm-diameter sample.

Electron beam irradiation (EBI) technology has been widely used in industrial fields during the welding process, and the instantaneous high temperature produced during this process is a significant advantage for the synthesis of metallic materials. Here, we report a method to manufacture metal/oxide nanocomposite materials by EBI using oxide films. The CoO films are first prepared by a pulsed-laser deposition technique, and the as-prepared films are treated by EBI with different electron doses. CoO can be controllably reduced to metallic Co, and a Co/CoO nanocomposite is produced with a large number of oxygen vacancies after EBI. The self-assembled well-dispersed Co nanoparticles are formed on the film surface, and their sizes can be controlled by the electron dose and irradiation time. The obtained Co/CoO composited nanoparticle films exhibit an exchange bias effect, and their blocking temperature can be modified by variations in the electron dose and time.

The carbon doped RMn1.7Cr0.3Si2C (R = Nd, Sm, Dy) compounds were prepared by arc melting and investigated using room temperature (RT) X-ray diffraction (XRD), neutron powder diffraction (NPD) and magnetic measurements. Carbon atoms were found to occupy the interstitial site (0, 0, 0.125) in a superstructure with the space group P4/mmm at room temperature. There exists a disordered substitution between the R atoms and corresponding Si dumbbells on the same layer perpendicular to c direction in the carbides. The Mn/Cr sublattice of the carbides exhibits ferromagnetic characteristics at room temperature despite of a very short intralayer interatomic distance (dMn-Mn = 2.796 A for R = Dy), which is far below the critical distance for a ferromagnetic (dMn-Mn >2.87 A) ordering of Mn sublattice due to the strong hybridization between the interstitial C and the Mn/Cr atoms. Different phase transitions of the carbides have different response to the external magnetic field. These carbides provide the potential for further research on magneto-transport properties and magnetocaloric effect. Additionally, spin reorientation was observed in SmMn1.7Cr0.3Si2C owing to the competence of magnetocrystalline anisotropy between the Mn/Cr sublattice and the Sm sublattice.

We investigate the magnetic properties of a chemically heterogeneous binary-main-phase (BMP) Nd-Ce-Fe-B magnet with a core-shell structure via micromagnetic simulation. It is found that the coercivity strongly depends on the shell thickness. The BMP magnet's coercivity initially increases and then decreases with increasing Nd-rich shell thickness, and so there is the optimal shell thickness which shows the maximum coercivity for any given Ce concentration. The simulation shows the significant difference in coercivity and maximum energy product between the BMP and single-main-phase magnets. Notably, the magnetization reversal mechanism of the BMP magnet is revealed in the simulation. Local reversals in the BMP magnet first occur in the Ce-rich shells, followed by the Nd-rich cores. Then, the magnetization in Ce-rich core/Nd-rich shell typed grains is switched after reversed magnetization of all the Nd-rich core/Ce-rich shell typed grains. The BMP magnet represents a further increased coercivity for a larger GB thickness, which can be well explained by a maximum stray field.

In situ high-temperature XRD and magnetic field heat treatment (MFHT) under a magnetic field of 50 kOe have been used to investigate the structural and magnetic properties of the D022 Mn3−xGa (x = 0, 0.2, and 0.4). It was found that Mn3−xGa compounds maintain ferrimagnetic D022 phase in the temperature range of 300–700 K, and their magnetic properties were remarkably improved through MFHT. The saturation magnetization (Ms) of Mn3.0Ga at 300 K increased by 37% from 18.3 to 25.0 emu/g after MFHT. All Mn3-xGa samples showed superior thermal stability in magnetization from 300 to 500 K, and they still retained excellent magnetic properties at a temperature of up to 700 K. The magnetization of Mn3.0Ga and Mn2.8Ga showed a positive temperature coefficient from 300 to 400 K. Even at 700 K, Ms and Hc of 24.3 emu/g and 4.5 kOe were retained in Mn2.8Ga, which is excellent for high-temperature applications. In addition, the coercivity mechanism of Mn3−xGa at 700 K was illustrated by minor hysteresis loops measurement, and it was found that the coercivity mechanism of Mn3−xGa at 700 K was dominated by the pinning mechanism.

Nanostructural anisotropic MnBi films with strong out-of-plane orientation were prepared by pulsed laser deposition and subsequent heat treatment. The orientation and particle size of MnBi films can be controlled by altering those of the Bi template-layers. Under the optimal treatment, a room temperature coercivity as high as 27.4 kOe was obtained in the nanostructural MnBi films. This high coercivity stems from the complete isolation in Bi matrix of refined MnBi clusters, within which MnBi nanoparticles are magnetically coupled. As the size of MnBi clusters decreases, the magnetization process of the nanostructural MnBi films changes from non-uniform rotation to uniform rotation of magnetic moments.

A D0 22 -type super structure with a formula Mn 6‐y Ga 2 + y (0 ≤ y ≤ 1.64) is proposed to describe the structural evolution of tetragonal Mn 3‐x Ga (0 ≤ x ≤ 1.8) intermetallic compounds. Degree of site disorder is obtained based on the 2 b -site Mn and 2 a -site Ga disordering model. Neutron data refinement indicates that the structure transforms from a completely ordered state ( y = 0) to the 2 a and 2 b sites (Mn-Ga) disordered state ( y > 0.92) with increasing y . The ferrimagnetic ordering structure between Mn (4 d ) and Mn (2 a /2 b ) has been established, with the magnetic moment retaining almost 2.2 μ B and ranging from − 3.3 μ B ( y → 0) to − 2.3 μ B ( y → 1.64), respectively.

Valleytronics is a promising paradigm to explore the emergent degree of freedom for charge carriers on the energy band edges. Using ab initio calculations, we reveal that the honeycomb boron nitride (h-BN) monolayer shows a pair of inequivalent valleys in the vicinities of the vertices of hexagonal Brillouin zone even without the protection of the C3 symmetry. The inequivalent valleys give rise to a 2-fold degree of freedom named the valley pseudospin. The valley pseudospin with a tunable bandgap from deep ultraviolet to far-infrared spectra can be obtained by doping h-BN monolayer with carbon atoms. For a low-concentration carbon periodically doped h-BN monolayer, the subbands with constant valley Hall conductance are predicted due to the interaction between the artificial superlattice and valleys. In addition, the valley pseudospin can be manipulated by visible light for high-concentration carbon doped h-BN monolayer. In agreement with our calculations, the circularly polarized photoluminescence spectra...

Multiferroic materials have the potential to be applied in novel magnetoelectric devices, for example, high-density non-volatile storage devices. During the last decades, research on multiferroic materials was focused on three-dimensional (3D) materials. However, 3D materials suffer from dangling bonds and quantum tunneling in nano-scale thin films. Two-dimensional (2D) materials might provide an elegant solution to these problems, and thus are highly in demand. Using first-principles calculations, we predicted ferromagnetism and electric-field-driving ferroelectricity in the monolayer and even in the few-layers of CuCrP2S6. Although the total energy of the ferroelectric phase of the monolayer is higher than that of the antiferroelectric phase, the ferroelectric phases can be realized by applying a large electric field. Besides the degrees of freedom in the common multiferroic materials, the valley degree of freedom is also polarized, according to our calculations. The spins, electric dipoles and valleys are coupled with each other as shown in the computational results. In our experiment, we observed the out-of-plane ferroelectricity in few-layer CuCrP2S6 (approximately 13 nm thick) at room temperature. 2D ferromagnetism of few-layers is inferred from the magnetic hysteresis loops of the massively stacked nanosheets at 10 K. The experimental observations support our calculations very well. Our findings may provide a series of 2D materials for further device applications.

Magnetic properties of single perovskite-structure epitaxial film are reported to have layered distribution recently. However, the different responses of spin configurations in individual layers to the variation of temperature and strain state, especially the subtle response of layered film due to structural phase transformation of SrTiO3 (STO) substrate around 105 K, have not been revealed completely. Drastic drop and concomitant abnormal increase of remnant magnetic moments (REM) and coercivity of low-doped La1-xSrxMnO3 (x=0.175) /SrTiO3 film were observed for the first time around 105 K only in the in-plane direction, and layered magnetic structures were further inferred based on investigation of microstructure, strain distribution and chemical inhomogeneity. Abnormal change of magnetic properties around 105 K was discussed by a three-layer model, in which softer ferromagnetic layer was supposed to form in the middle layer of strain induced layered structure, and the spin configuration of middle layer underwent non-synchronous transformation relative to other parts of the film, which may be attributed to the change of in-plane strain inside the film around 105 K. Our work reveals the variation of individual magnetic layers with the increase of temperature through utilizing the remnant magnetic field in measuring system, and the abrupt reversal of spin configuration at the intermediate layer can also serve the design of novel spintronics devices in the future.

The sphericity, κ, is introduced to describe the morphology of the magnetic grains. The effect of κ on the magnetic properties of rare earth-transition metal (RE-TM) permanent magnets was investigated using the micromagnetic simulation, where randomly aligned, irregular-shaped grains with ferromagnetic/non-ferromagnetic grain boundary (GB) phases were considered. For the simulated RE-TM systems, the coercivity increases significantly with the increase in κ. In particular, with 10 nm thick non-ferromagnetic GB phase, the coercivity, 1.74 MA/m, for к = 0.9 increases by 22% compared to 1.43 MA/m for к = 0.6 in the Nd2Fe14B system. Among the simulated materials, the SmCo5 system displays the largest increment in coercivity, increasing by 0.82 MA/m from 7.61 MA/m for к = 0.6 to 8.43 MA/m for к = 0.9. Magnetization reversal patterns under different external fields indicate that the dependence of coercivity on κ is attributed to the formation of local reversals at different regions and mechanisms of reversal propagation. Meanwhile the effect of κ cannot be neglected even at elevated temperatures. The simulated results of (Dy0.47Nd0.53)2Fe14B systems with the non-ferromagnetic GB layer of 4 nm at a temperature of 450 K show that the coercivity for к = 0.9 (1.88 MA/m) increased by 23% compared with that of к = 0.6 (1.52 MA/m). Our study demonstrates that the sphericity can be used as a key parameter to design high-coercivity RE-TM magnets.

A comprehensive study of the structural and magnetic properties of the Ni2Mn1.48Sb0.52 compound is presented using neutron diffraction and magnetic measurements. It is found that Mn atoms on 4a and 4b sites are ferrimagnetic coupled in the austenitic phase. At 300 K, the magnetic moments of Mn (4a) and Mn (4b) are determined to be 2.72(3) μB and − 2.67(5) μB, respectively. From 260 K to 4 K, the compound is in martensite phase and the magnetic moments of Mn (2a), Mn (2f), Mn (2b), Mn (2e) at 4 K are 2.2(5) μB, 2.3(5) μB, − 2.1(5) μB, and − 2.6(5) μB, respectively.