Magnetic and Distribution of Magnetic Moments in Amorphous Fe89.TP10.3 Alloy Nanowire Arrays

Binary amorphous Fe89.7P10.3 alloy nanowire arrays in been fabricated in an anodic aluminium oxide template diameter of about 40nm and length of about 3μm have by electrodeposition. Magnetic properties of the samples are investigated by mean of vibrating sample magnetometer, transmission Mossbauer spectroscopy and conversion electron Mossbauer spectroscopy at room temperature. It is found that the nanowire arrays have obvious perpendicular magnetic anisotropy, and are ferromagnetic at room temperature, with its Mossbauer spectra consisting of six broad lines. The average angles between the Fe and 28° at the end of the amorphous Fe89.7P10.3 alloy magnetic moment and the wire axis are about 14°inside nanowire arrays, respectively. The magnetic behaviour is decided by the shape anisotropy and the dipolar interaction between wires. In addition, the magnetic moments distribution is theoretically demonstrated by using the symmetric fanning mechanism of the spheres chain model.

Microwave Magnetic Properties and Natural Resonance of e-Co Nanoparticles

Owing to the novel crystal structure, ε-Co nanoparticles with an average diameter of 12 nm are synthesized and the microwave magnetic properties of the epoxy resin composite with 50voi% ε-Co particles are measured in the frequency range 0.1-7 GHz. The experimental resonance frequency （4.7 GHz） matches well with the values obtained by the theoretical calculation with the Kittel equation and fitting the experimental permeability dispersion curve via the Landan-Lifshitz equation. Hence the resonance peak is attributed to natural resonance mode. This work is believed to be beneficial for further understanding microwave applications of the novel ε-Co nanoparticles.

Electromagnetic wave absorption properties of Ba(CoTi)_(x)Fe_(12-2x)O_(19)@BiFeO_(3)in hundreds of megahertz band

The high-performance electromagnetic(EM)wave absorption material Ba(Co Ti)_(x)Fe_(12-2x)O19@Bi Fe O_(3)was prepared by solid-state reaction,and its EM wave absorption properties were deeply studied.The results revealed that Ba(Co Ti)x Fe12-2x O19@Bi Fe O_(3)could obtain excellent absorption properties in hundreds of megahertz by adjusting the Co^(2+)-Ti^(4+)content.The best comprehensive property was obtained for x=1.2,where the optimal reflection loss(RL)value reaches-30.42 d B at about 600 MHz with thickness of 3.5 mm,and the corresponding effective absorption band covers the frequency range of 437 MHz-1 GHz.Moreover,the EM wave absorption mechanism was studied based on the simulation methods.The simulated results showed that the excellent EM wave absorption properties of Ba(Co Ti)_(x)Fe_(12-2x)O19@Bi Fe O_(3)mainly originated from the internal loss caused by natural resonance,and the interface cancelation further improved the absorption properties and resulted in RL peaks.

Improvement in Structural and Magnetic Properties of Electrospun Ni_1-xCu_xFe₂O₄Nanofibers

A series of Ni1-xCuxFe2O4 (0.0 ≤ x ≤ 1.0) nanofibers have been synthesized employing electrospinning method at 650°C. The effect of Cu substitution on structural, morphology and magnetic properties of NiFe2O4 nanofibers is reported. The XRD analysis showed the formation of single-phase cubic spinel Ni-Cu ferrite and an increasing behavior of lattice constant. The surface morphology is characterized by SEM, it is investigated that nanofibers have uniform and continuous morphology. The VSM results showed Cu substitution played an important role in magnetic properties of Ni1-xCuxFe2O4. The saturation magnetization (Ms) decreases linearly with increasing Cu2+ content, while coercivity (Hc) has slowly decreased before x ≤ 0.5, and then sharply increased to 723.9 Oe for x = 1.0. The magnetic properties of Ni1-xCuxFe2O4 can be explained in Neel’s model, cation distribution and shape anisotropy.

Influence of high-pressure heat treatment on magnetocaloric effects and magnetic phase transition in single crystal Gd_(3)Ga_5O_(12)

The magnetic properties and magnetic phase transition critical behavior of Gd_(3)Ga_5O_(12)single crystals subjected to high-pressure heat treatment were investigated.The results show that high-pressure heat treatment reduces the Curie temperature and magnetization of the sample.Under a magnetic field change of 5 T,the maximum isothermal magnetic entropy of the sample is approximately 19.73 J/(kg·K).High-pressure heat treatment increases the phase transition temperature range and leads to an increase in the magnetic refrigeration power.Both Gd_(3)Ga_(5)O_(12)single crystals and the high-pressure heat-treated sample undergo a second-order phase transition.The critical behavior of the samples aligns with the mean field model acquired via critical model fitting.This indicates that the samples exhibit long-range exchange interactions in the system near the Curie temperature.Thus,this material can be used as a magnetic refrigerant for low-temperature applications.

Influence of nano-diamond content on the microstructure,mechanical and thermal properties of the ZK60 composites

The effect of nano diamond(ND)content on the microstructure,mechanical properties,and thermal conductivity of ZK60+x(x=0,0.05,0.1,0.15,0.2 wt.%)ND composites were investigated.The microstructures of ND/ZK60 composites were observed,which indicated that the nanoscale MgZn_(2) and ND particles distributed evenly in theα-Mg matrix.The tensile yield strength(TYS)and compressive yield strength(CYS)of the composites first increased remarkably and then decreased with further increasing the ND content.Due to the surface area of the matrix-diamond interface increased and the grains sizes of composites decreased with the amount of ND increase,which cause the coefficient of thermal expansion(CTE)of the composites reduced significantly.Meanwhile,the thermal conductivity of the composite material decreases from 129 W·m^(−1)·K^(−1) to 116 W·m^(−1)·K^(−1) with the content of ND increasing from 0.05%to 2.0%.The thermal conductivity of the composites increases to the maximum and then decrease with the increase of temperature(in temperature range of 273-573 K).The ZK60+0.05 ND showed superior mechanical and thermal conductivity property,TYS of 343.97 MPa,CYS of 341.74 MPa,elongation of 15.71%,CTE of 7.3×10^(−6)K^(−1),and thermal conductivity of 129 W·m^(−1)·K^(−1) at room temperature.It is demonstrated that the ND content has an obvious influence on the microstructure,mechanical properties,and thermal conductivity of ND/ZK60 composites.

Magnetic transition behavior of perovskite manganites Nd0.5Sr0.3Ca0.2MnO3 polycrystalline

A polycrystalline sample Ndo.5Sro.3Cao.2MnO3 is prepared by the conventional solid state reaction method. The structure and magnetic properties are investigated with x-ray diffraction （XRD） patterns, a superconducting quantum in- terference device （SQUID）, and electron spin resonance （ESR）. The sample is in single phase with the space group Pbnm symmetry. With the decrease of temperature, Ndo.sSro.3Cao.2MnO3 undergoes three magnetic transitions： ferromagnetic transition at Tc ≈ 210 K, charge-ordering at Tco ≈ 175 K, and antiferromagnetic transition at TN = 155 K. In addition, the activation energy Ea ≈ 52.78 meV can be extracted by curve fitting.

Calculation of High Frequency Complex Permeability of Carbonyl Iron Flakes in a Nonmagnetic Matrix

The carbonyl iron flakes are fabricated by high-energy ball milling. The effective permeability is measured and calculated for the composite consisting of flakes embedded in a nonmagnetic matrix. The magnetic flakes with a shape anisotropy and random spatial distribution of normal direction are considered to calculate the complex permeability of magnetic flake materials. Its analytical model is derived from the Landau-Lifshitz-Gilbert equation and Bruggeman ＇s effective medium theory. The calculated results agree well with the experiment.

Microwave Magnetic Properties of Nd2Fe17N3-δ with Planar Anisotropy

Microwave magnetic properties are studied for rhombohedral structure Nd2Fe17N3-δ with planar magnetic anisotropy. Its resin composites show the permeability μ＇0 = 4.15 at low frequency, the natural resonance frequency fT = 1.71 GHz and the resonance bandwidth 6.66 GHz. The calculated static permeability of Nd2Fe17N3-δ reaches 133. The microwave magnetic properties are determined by the c-axis anisotropy field, basal plane anisotropy field and high saturation magnetization. Based on microwave measurement and theoretical fitting on complex permeability spectra, Nd2Fe17N3-δ may be a promising microwave absorber with bandwidth wider than traditional hexaferrites materials in GHz ranges.

Influence of shape anisotropy on microwave complex permeability in carbonyl iron flakes/epoxy resin composites

To explore the mechanism of carbonyl iron flake composites for microwave complex permeability, this paper investigates the feature of the flakes. The shape anisotropy was certified by the results of the magnetization hysteresis loops and the Mossbauer spectra. Furthermore, the shape anisotropy was used to explain the origin of composite microwave performance, and the calculated results agree with the experiment. It is believed that the shape anisotropy dominates microwave complex permeability, and the natural resonance plays main role in flake.

Analyzing Bandwidth on the Microwave Absorber by the Interface Reflection Model

Metallic flaky sendust particles are prepared for use as fillers in electromagnetic attenuation composites. We report the interface reflection model to divide the broad bandwidth into electromagnetic loss and quarter-wavelength （λ/4） cancelation. Combining with the face reflection calculation, we identify the electromagnetic loss originated from skin effect, which is used to explain over half of the absorbed energy in high frequency band. Most impor- tantly, the unique electromagnetic loss cannot generate the reflection loss （RL） peak. Using the phase relation of face reflection, we show evidence that the λ/4 cancelation is vital to generate the RL peak. The calculated energy loss agrees well with the experimental data and lays the foundation for further research.

Microwave reflection properties of planar anisotropy Fe_(50)Ni_(50) powder/paraffin composites

The reflection properties of planar anisotropy Fe50Ni50 powder/paraffin composites have been studied in the microwave frequency range.The permeability of Fe50Ni50 powder/paraffin composites is greatly enhanced by introducing the planar anisotropy,and can be further enhanced by using a rotational orientation method.The complex permeability can be considered as the superposition of two types of magnetic resonance.The resonance peak at high frequency is attributed to the natural resonance,while the peak at low frequency is attributed to the domain-wall resonance.The simulated results of the microwave reflectivity show that the matching thickness,peak frequency,permeability,and permittivity are closely related to the quarter wavelength matching condition.The Fe50Ni50 powder/paraffin composites can be attractive candidates for thinner microwave absorbers in the L-band(1-2 GHz).

Magnetic properties and magnetic entropy change of perovskite manganites La_(0.9-x)Eu_xSr_(0.1)MnO_3(x=0.000,0.075) by experimental method and numerical fitting

Polycrystalline samples La_(0.9-x)EuxSr_(0.1)MnO_3(x = 0.000, 0.075) were prepared by the standard solid-state reaction method. The results show that the samples preform a characteristic of clusters spin-glass state at low temperature. The samples show a characteristic of ferromagnetism(FM) characteristic in the temperature range of 15-125 K and 15-150 K respectively; the samples show preformed clusters in the temperature range of 125-343 K and 150-325 K, respectively, the samples show paramagnetism(PM)characteristic above 343 and 325 K, respectively. The second-order transitions are found at 118 and 135 K for undoped and doped sample, respectively. When the applied magnetic field is 7 T, the maximum magnetic entropy change |△S_M| value of the samples is near the Curie temperature(Tc), and the value of|△S_M| reaches 2.76 and 3.03 J/(K kg), respectively. In addition, the relative cooling power(RCP) is found to be 425.28 and 443.53 J/kg. The numerical fitting data fit well with experimental data. These results indicate that both the samples have the potential to realize magnetic refrigeration in the high temperature region(T > 77 K).

Cation ratio and oxygen defects for engineering the magnetic transition of monodisperse nonstoichiometric zinc ferrite nanoparticles

Monodisperse nonstoichiometric zinc ferrite nanoparticles with a tunable size of 4.1–32.2 nm are fabricated via thermal decomposition. An extrinsic impurity phase of the ZnO component is present in the zinc ferrite nanoparticles with a size of <10 nm, but this phase can be eliminated after the air annealing treatment. The atom ratio of Zn/Fe and concentration of oxygen vacancies decrease as the particle size of zinc ferrite increases, causing magnetic transition from superparamagnetism to ferromagnetism. The X-ray magnetic circular dichroism spectra reveal that the spin magnetic moments of Fe^(3+)are reduced, and the orbital magnetic moments are frozen with the increasing atom ratio of Zn/Fe. Therefore,saturation magnetization decreases. The saturation magnetizations of all the zinc ferrite nanoparticles decrease after the air annealing treatment, suggesting that oxygen vacancies considerably influence the magnetic properties. The air annealing treatment can minimize the number of oxygen defects,which trigger some of the Fe^(3+)–OV–Fe^(3+)ferrimagnetic couplings to transfer into the Fe^(3+)–O^(2-)–Fe^(3+)antiferromagnetic couplings. This work provides new insights regarding the magnetic performance of spinel ferrites by tuning the stoichiometric ratio and oxygen defects.

Influence of deposition time on the morphology and optical properties of SiO_2-ZnO composite photonic crystals

SiO2 photonic crystal were successfully prepared by vertical deposition and then used as a template to fabricate SiO2-ZnO composite photonic crystals on ITO substrates by electrodeposition and subsequent calcination. A number of different deposition times were used. The morphologies of the silica opals and SiO2-ZnO composite photonic crystals were investigated by scanning electron microscopy. It was found that ZnO particles grew randomly on the surfaces of the silica spheres when the deposition time was short. As the deposition time was increased, the ZnO particles grew evenly on the surfaces of the silica spheres so that the interstitial space of the silica template was filled with ZnO particles. Reflectance spectra of the SiO2-ZnO composite crystals revealed that all of the fabricated photonic crystals exhibit a photonic band gap in the normal direction.

Macroscopic,artificial active matter

Artificial active matters on a macroscopic scale,including vibrating particles,robots,and camphor boats,have attracted increasing attentions due to their uniform properties,rich and easily controllable parameters,convenient observation,and the independence of biochemical processes from physical processes,especially providing these unique advantages for researching the collective behaviors under strong confinement and crowded surroundings.In this review,we present an overview of motion models,mechanisms,and dynamic characteristics of various active particles,both in free and complex media.Additionally,we delve into the collective behaviors of“dry”active matter,covering structural and dynamic properties observed in experiments and theoretical models.We summarize the impact of hydrodynamic interactions on the dynamics and structures of these active particles within hydrodynamic environments.Lastly,we discuss emerging opportunities and challenges for future advancement of macroscopic artificial active matter.

Covalent carbene modification of 2D black phosphorus

Black phosphorus(BP)has attracted an ever-growing interest due to its unique anisotropic two-dimensional structure,impressive photoelectronic properties and attractive application potential.However,the tools for bandgap engineering and passivation via covalent modification of BP nanosheets remain limited to diazonium salt and nucleophilic addition methods,so that developing new modification strategies for BP nanosheets is crucial to explore its physical and chemical properties and enrich the toolbox for functionalization.Herein,we report the covalent modification of liquid-phase exfoliated BP nanosheets based on a rational analysis of BP structure.The modification of BP is achieved via carbene,a highly reactive organic mediate.The carbene modification improves the solubility and stability of BP nanosheets.Detailed microscopic and spectroscopic characterizations including infrared spectra,Raman spectra,X-ray photoelectron spectra,SEM and TEM were conducted to provide insights for the reaction.The proof of the existence of covalent bonds between BP nanosheets and organic moieties confirms the successful modification.Moreover,theoretical calculations were conducted to unveil the reaction mechanism of the two different types of bonds and the chemical property of two-dimensional BP.

Quantitative reorientation behaviors of macro-twin interfaces in shape-memory alloy under compression stimulus in situ TEM

Twinning stress is known to be a critical factor for the actuating performance of magnetic shape memory alloys because of the harmful deterioration of their magnetic field-induced strain effect.However,the intrinsic origin of the high twinning stress is still in debate.In this work,we firstly fill this gap by precisely probing the reorientation behaviors of A-C and A-B two common macro-twin interfaces under the stimulus of uniaxial compression in-situ transmission electron microscope.The grain boundary is proved to be the main reason for large twinning stress.The twinning stress of the A-C and A-B type interfaces quantitatively are~0.69 and 1.27 MPa within the plate respectively.The A-C type interface evidently has smaller twinning stress and larger deformation variable than the A-B interface.Under the action of compression,not only the orientations of the crystals have changed,but also the roles of the major and minor lamellae have changed for both interfaces due to the movements of twinning dislocations.Combining insitu and quasi in-situ electron diffraction data,the reorientation process is clearly and intuitively shown by the stereographic projection.Atomic models and the theory of dislocation motion are proposed to phenomenologically clarify the intrinsic mechanism.This work is believed to not only provide a deeper understanding of the deformation mechanism of magnetic shape memory alloys under uniaxial compression testing,but also discover that compression training is not the mechanical training way to decrease the twinning stress of non-modulated martensite in single crystal shape memory alloys.

Regulated adsorption sites using atomically single cluster over biochar for efficient elemental mercury uptake

Carbon-based materials have been widely used in gaseous pollutant removal because of their sufficient surface functional groups;however,its removal efficiency for elemental mercury(Hg^(0))is low.In this study,we fabricated biomass using a chelated coupled pyrolysis strategy and further constructed the regulated adsorption sites for gaseous Hg^(0) uptake.A series of Mnδ-N_(2)O_(2)/BC with different manganese cluster sizes demonstrated that manganese clusters anchored on biochar acted as highly active and durable adsorbents for Hg^(0) immobilization,which increased the adsorption efficiency of Hg^(0) by up to 50%.Shrimp-and crab-based biochar adsorbents exhibited excellent Hg^(0) removal because of their chitosan-like structure.In particular,small Mn clusters and oxygen species around the defect led to a boost in the Hg^(0) adsorption by carbon.The results of density functional theory calculation revealed that the presence of oxygen in the carbon skeleton can tune the electrons of small-sized Mn clusters,thereby promoting the affinity of mercury atoms.The newly developed Mnδ-N_(2)O_(2)/BC_(shrimp) had an adsorption capacity of 7.98-11.52 mg g^(−1) over a broad temperature range(50-200℃)and showed a high tolerance to different industrial flue gases(H_(2)O,NO,HCl,and SO_(2)).These results provide novel green and low-carbon disposal methods for biomass resource utilization and industrial Hg^(0) emission control.

A micron-sized GMR sensor with a CoCrPt hard bias

A GMR（giant magneto-resistive） spin valve sensor for magnetic recording has been designed in an attempt to solve the Barkhausen noise problem in small-sized GMR sensors.In this study,the GMR ratio of the top-pinned spin valve is optimized to a value of 13.2%.The free layer is magnetized perpendicular to the pinned layer by a CoCrPt permanent magnetic bias so that a linear magnetic field response can be obtained.An obvious improvement on performance is observed when the permanent magnetic bias is magnetized,while the GMR sensor has a steadier MR-H loop and a smaller coercive field.