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.

The study of the shape anisotropy in patterned permalloy films

In this paper a systematic ferromagnetic resonance study shows that an in-plane magnetic anisotropy in the patterned micron octagon permalloy （Ni80Fe20） elements is mainly determined by the element geometry. The easy-axis is along the edge of the elements, and the hard-axis is along the diagonal. The shape anisotropy of the octagon elements is determined by square and equilateral octagon, and the theoretical calculation was studied on the shape anisotropy. The shape anisotropy of rectangular was calculated by using the same theory.

Shape Anisotropy and Resonance Mode Guided Reliable Interconnect Design for In-plane Magnetic Logic

Dipole coupled nanomagnets controlled by the static Zeeman field can form various magnetic logic interconnects.However, the corner wire interconnect is often unreliable and error-prone at room temperature. In this study, we address this problem by making it into a reliable type with trapezoid-shaped nanomagnets, the shape anisotropy of which helps to offer the robustness. The building method of the proposed corner wire interconnect is discussed,and both its static and dynamic magnetization properties are investigated. Static micromagnetic simulation demonstrates that it can work correctly and reliably. Dynamic response results are reached by imposing an ac microwave field on the proposed corner wire. It is found that strong ferromagnetic resonance absorption appears at a low frequency. With the help of a very small ac field with the peak resonance frequency, the required static Zeeman field to switch the corner wire is significantly decreased by ~21 m T. This novel interconnect would pave the way for the realization of reliable and low power nanomagnetic logic circuits.

Microwave Application Shape Anisotropy of Micro-sized Bamboo Blind Shape

Electromagnetic anisotropic characteristics in micro-sized water bamboo blind shape are observed by high frequency electromagnetic computation,which is applied to the material constants estimation.In assuming that the micro-sized unit structure is repeated in 3-dimensional space and its size is much smaller than the electromagnetic wave length,the micro-sized electromagnetic field calculation is carried out.If the micro-structure shapes of the material are different even if they are the same volume rate,different dielectric constant characteristics are provided.The reasons are considered to be a generation of de-electrification within the dielectric material.

Fabrication and magnetic properties of Ni_(0.5)Zn_(0.5)Fe_2O_4 nanofibres by electrospinning

NiZn ferrite/polyvinylpyrrolidone composite fibres were prepared by sol,el assisted electrospinning. Ni0.5Zn0.5Fe2O4 nanofibres with a pure cubic spinel structure were obtained subsequently by calcination of the composite fibres at high temperatures. This paper investigates the thermal decomposition process, structures and morphologies of the electrospun composite fibres and the calcined Ni0.5Zn0.5Fe2O4 nanofibres at different temperatures by thermo-gravimetric and differential thermal analysis, x-ray diffraction, Fourier transform infrared spectroscopy and field emission scanning electron microscopy. The magnetic behaviour of the resultant nanofibres was studied by a vibrating sample magnetometer. It is found that the grain sizes of the nanofibres increase significantly and the nanofibre morphology graduMly transforms from a porous structure to a necklace-like nanostructure with the increase of calcination tempera-ture. The Ni0.5Zn0.5Fe2O4 nanofibres obtained at 1000℃ for 2h are characterized by a necklace-like morphology and diameters of 100-200nm. The saturation magnetization of the random Ni0.5Zn0.5Fe2O4 nanofibres increases from 46.5 to 90.2 emu/g when the calcination temperature increases from 450 to 1000℃. The coercivity reaches a maximum value of 11.0 kA/m at a calcination temperature of 600℃. Due to the shape anisotropy, the aligned Ni0.5Zn0.5Fe2O4 nanofibres exhibit an obvious magnetic anisotropy and the ease magnetizing direction is parallel to the nanofibre axis.

Demagnetizing factors in patterned CoNiFe films with rectangular elements

CoNiFe patterned films with rectangular elements, all 600-nm wide but of different lengths, were fabricated and inves- tigated by ferromagnetic resonance experiment and micromagnetic simulation. An in-plane magnetic uniaxial anisotropy was exhibited, and its value increases with the increase of the aspect ratio of the elements, which was fitted by the model, including a quasi-ellipsoid demagnetizing field and a non-uniform demagnetizing field. The relative importance of the non- uniform demagnetizing field decreased from 0.26 to 0.16 with the increase of the length-width aspect ratio of the patterned element from 1.5 to 10. The demagnetizing factors in the three principal axes were determined from the experimental data of ferromagnetic resonance, which agreed reasonably well with the values calculated by micromagnetic simulation. The calculation also indicated that the interaction between elements could be neglected when the edge-to-edge spacing between neighboring elements was larger than 3 μm in our patterned films.

Shape anisotropic Fe3O4 nanotubes for efficient microwave absorption

Although Fe3O4 particles have exhibited excellent microwave absorbing capacity and widely used in practical application due to the synergistic effect of magnetic loss and dielectric loss,their applications are still limited for the required high mass fraction in absorbers.To overcome this problem,the development of Fe3O4 materials with low dimensional structures is necessary.In this study,the shape anisotropic Fe3O4 nanotubes(NTs)with low mass ratios were applied to realize efficient microwave absorption.The NTs with different aspect ratios were prepared through facile electrospinning followed by two-step thermal treatments and mechanical shearing.The cross-linked nanotubular structure enabled the absorbers to have much higher electrical conductivity,multiple scattering,polarization relaxation and better anti-reflection surface,while the shape anisotropic NTs maintained significant multiple resonances with stronger coercivity.These all were beneficial to microwave absorption with enhanced dielectric loss,magnetic loss and sterling impedance matching.Results showed that the absorber with 33.3 wt.%of short Fe3O4 NTs had minimum reflection loss of-58.36 dB at 17.32 GHz with a thickness of 1.27 mm,and had the maximum effective absorbing bandwidth(EAB)of 5.27 GHz when the thickness was 1.53 mm.The absorber with 14.3 wt.%of long Fe3O4 NTs presented the widest EAB in certain radar band with attenuated 80.75%X band and 85%Ku band energy bellow-10 dB at the thickness of 2.65 and 1.53 mm,respectively.This study provided an approach for the development of shape anisotropic magnetic absorbing materials,and broadened their practical applications as magnetic absorbers.

Controllable preparation and microwave absorption properties of shape anisotropic Fe_(3)O_(4) nanobelts

To substantially prevent electromagnetic threatens,microwave absorbing materials(MAMs)are required to eliminate surplus electromagnetic waves.As a typical MAM,Fe_(3)O_(4) particles with complex permittivity and permeability have been widely applied due to the coexistence of magnetic loss and dielectric loss.However,the necessary high mass fraction significantly limited its applications,thus Fe_(3)O_(4) nanostructures have been extensively investigated to overcome this problem.In this work,uniform Fe_(3)O_(4) nanobelts were prepared by electrospinning and two-step thermal treatment.By controlling the composition and viscosity of the electrospinning precursor solution,Fe_(3)O_(4) nanobelts with tunable lateral sizes(200 nme1 mm)were obtained.The samples with low content(only 16.7 wt%)Fe_(3)O_(4) exhibited wide maximum effective absorbing bandwidths(EAB)over 3 GHz,and Fe_(3)O_(4) nanobelts with smaller lateral sizes showed a maximum EAB of 4.93 GHz.Meanwhile,Fe_(3)O_(4) nanobelts with smaller lateral sizes presented superior reflection loss properties,the lowest reflection loss reached-53.93 dB at 10.10 GHz,while the maximum EAB was up to 2.98 GHz.The excellent microwave reflection loss of Fe_(3)O_(4) nanobelts was contributed to the enhanced synergistic effect of magnetic loss,dielectric loss,and impedance matching,originated from the hierarchically cross-linked networks and shape anisotropies.This study could broaden the practical applications of magnetic absorbers,and provided an approach for the development of shape anisotropic magnetic materials.

Magnetically Induced Anisotropic Interaction in Colloidal Assembly

The wide accessibility to nanostructures with high uniformity and controllable sizes and morphologies provides great opportunities for creating complex superstructures with unique functionalities.Employing anisotropic nanostructures as the building blocks significantly enriches the superstructural phases,while their orientational control for obtaining long-range orders has remained a significant challenge.One solution is to introduce magnetic components into the anisotropic nanostructures to enable precise control of their orientations and positions in the superstructures by manipulating magnetic interactions.Recognizing the importance of magnetic anisotropy in colloidal assembly,we provide here an overview of magnetic field-guided self-assembly of magnetic nanoparticles with typical anisotropic shapes,including rods,cubes,plates,and peanuts.The Review starts with discussing the magnetic energy of nanoparticles,appreciating the vital roles of magneto-crystalline and shape anisotropies in determining the easy magnetization direction of the anisotropic nanostructures.It then introduces superstructures assembled from various magnetic building blocks and summarizes their unique properties and intriguing applications.It concludes with a discussion of remaining challenges and an outlook of future research opportunities that the magnetic assembly strategy may offer for colloidal assembly.

Self-Assembled Plasmonic Pyramids from Anisotropic Nanoparticles for High-Efficient SERS

Surface-enhanced Raman scattering(SERS)substrates play important roles for the enhancement of inelastic scattering signals.Traditional substrates such as roughened electrodes and colloidal aggregates suffer from well-known signal reproducibility issues,whereas for current dominant two-dimensional planar systems,the hot spot distributions are limited by the zero-,one-or two-dimensional plane.The introduction of a three-dimensional(3D)system such as a pyramid geometry breaks the limitation of a single Cartesian SERS-active area and extends it into the z-direction,with the tip potentially offering additional benefits of strong field enhancement and high sensitivity.However,current 3D pyramidal designs are restricted to film deposition on prepared pyramid templates or self-assembly in pyramidal molds with spherical building blocks,hence limiting their SERS effectiveness.Here,we report on the fabrication of a new class of low cost and well-defined plasmonic nanoparticle pyramid arrays from different anisotropic shaped nanoparticles using combined top-down lithography and bottom-up self-assembly approach.These pyramids exhibit novel optical scattering properties that can be exploited for the design of reproducible and sensitive SERS substrate.The SERS intensity was found to decrease drastically in accordance with a power law function as the focal planes move from the apex of the pyramid structure towards the base.In comparison to sphere-based building blocks,pyramids assembled from anisotropic rhombic dodecahedral gold nanocrystals with numerous sharp tips exhibited the strongest SERS performance.Graphical Abstract Macroscale pyramidal array films with plasmonic tunability as a new class of SERS substrate for sensitive detection of chemicals.