Magnetic Field Alignment Research Articles

Improved thermal conductivity of carbon-based thermal interface materials by high-magnetic-field alignment

Carbon-based fillers for thermal interface materials (TIMs) are attractive due to their advantages such as high thermal conductivity, low thermal expansion, mechanical strength, flexibility, and low weight. In this work, we report a 330% enhancement of the through-plane thermal conductivity (kth) of a graphite-polymer composite TIM film by vertically aligning the graphite fillers with a 10 T superconducting magnet. The filler alignment is based on the large anisotropy in the magnetic susceptibility of graphite platelets. As the filler content increases from 10 to 60 wt%, the anisotropy of thermal conductivity (kth/kin) increases from 1.2 up to 2.3 for a perpendicular magnetic field alignment, whereas it remains the same for a parallel magnetic field alignment. The increased anisotropy is associated with better filler alignment at high filler loadings. This work provides a simple and effective solution to improve the physical properties of composite films by controlling their microstructure.

Magnetohydrodynamic Mixed Convective Flow Due to a Vertical Plate With Induced Magnetic Field

The steady hydromagnetic flow of a viscous, incompressible, perfectly conducting, and heat absorbing fluid past a vertical flat plate under the influence of an aligned magnetic field is studied. The flow is subject to mixed convective heat transfer. The fluid is assumed to have a reasonably high magnetic Prandtl number which causes significant-induced magnetic field effects. Such fluid flows find application in many magnetohydrodynamic devices including MHD power-generation. The effects of viscous dissipation and heat absorption by the fluid are investigated. The governing nonlinear partial differential equations are converted into a set of nonsimilar partial differential equations which are then solved using a spectral quasi-linearization method (SQLM). The effects of the important parameters on the fluid velocity, induced magnetic field, fluid temperature and as well as on the coefficient of skin-friction and the Nusselt number are discussed qualitatively.

Relations of the structure and thermal stability of NdFeB magnet with the magnetic alignment

Relationships between the alignment magnetic field Halign of NdFeB powders and the thermal stability of their sintered magnets were investigated on the base of observing the domain structure and microstructure. The thermal stability increased before 0.6 T and then decreased with the enhancement of Halign. The action of Halign is manifested in rotating magnetic particles and higher Halign increases the alignment degree of matrix phase and optimizes the magnet microstructure, thus increasing the magnetic ordering and minimizing the magnetostatic energy of aligned particles. Better magnetic ordering and lower magnetostatic energy are sensitive to the temperature, accounting for the reduction of thermal properties after 0.6 T.

Effect of aligned magnetic field on Casson fluid flow over a stretched surface of non-uniform thickness

Abstract In the study, we inspect the impact of cross diffusion and aligned magnetic field on Casson fluid flow along a stretched surface of variable thickness. The differential equations explaining the flow situation have been transitioned with the succor of suited transfigurations. The solution of the problem is achieved by using bvp5c Matlab package. From the solution, it is perceived that the flow, temperature and concentration fields are affected by the sundry physical quantities. Results explored for the flow over a uniform and a non-uniform thickness surfaces. The influence of emerging parameters on the flow, energy and mass transport are discussed with graphical and tabular results. Results show that the thermal, flow and species boundary layers are uneven for the flow over a uniform and non-uniform thickness stretched surfaces.

Additive manufacturing of anisotropic hybrid NdFeB-SmFeN nylon composite bonded magnets

In this work, we demonstrate a novel method of extrusion-based 3D printing additive manufacturing of bonded magnets comprising 65 vol% anisotropic composite powders of Dy-free magfine Nd-Fe-B and Sm-Fe-N in nylon. The 3D printing was performed using a big area additive manufacturing (BAAM) process. The effects of various post-printing alignment with different magnetic field intensities and temperatures on the properties of the anisotropic bonded Nd-Fe-B + Sm-Fe-N composite magnets were investigated. Remanence increases with alignment magnetic field leading to an increase in energy product, (BH)max. For anisotropic Nd-Fe-B + Sm-Fe-N composite bonded magnets with a 65 vol% loading fraction, (BH)max of up to 11.3 MGOe are obtained. In addition, the magnetic properties of the bonded magnets can be tuned through the post-printing alignment of anisotropic particles in different directions without impairing the original shape-changing effect. This technique shows great promise for producing anisotropic bonded magnets with enhanced magnetic properties.

The impact of aligned magnetic field on Walters Liquid $B$ fluid over a stretching surface with Rosseland diffusion approximation

In the present article, we have investigated the influence of inclined magnetic field on Walter's Liquid B fluid flow through stretching sheet. Elastic deformation and Rosseland diffusion approximation for radiative heat flux are considered. With the help of similarity transformation the flow and energy equations are solved analytically by using confluent hypergeometric method. Results for various physical parameters are presented through graphs. It's also noted that the increasing values of elastic deformation parameter increase the local Nusselt number.

Magnetotransport signatures of three-dimensional topological insulator nanostructures

We study the magnetotransport properties of patterned 3D topological insulator nanostructures with several leads, such as kinks or Y-junctions, near the Dirac point with analytical as well as numerical techniques. The interplay of the nanostructure geometry, the external magnetic field and the spin-momentum locking of the topological surface states lead to a richer magnetoconductance phenomenology as compared to straight nanowires. Similar to straight wires, a quantized conductance with perfect transmission across the nanostructure can be realized across a kink when the input and output channels are pierced by a half-integer magnetic flux quantum. Unlike for straight wires, there is an additional requirement depending on the orientation of the external magnetic field. A right-angle kink shows a unique $\pi$-periodic magnetoconductance signature as a function of the in-plane angle of the magnetic field. For a Y-junction, the transmission can be perfectly steered to either of the two possible output legs by a proper alignment of the external magnetic field. These magnetotransport signatures offer new ways to explore topological surface states and could be relevant for quantum transport experiments on nanostructures which can be realized with existing fabrication methods.

Glycosylated superparamagnetic nanoparticle gradients for osteochondral tissue engineering

In developmental biology, gradients of bioactive signals direct the formation of structural transitions in tissue that are key to physiological function. Failure to reproduce these native features in an in vitro setting can severely limit the success of bioengineered tissue constructs. In this report, we introduce a facile and rapid platform that uses magnetic field alignment of glycosylated superparamagnetic iron oxide nanoparticles, pre-loaded with growth factors, to pattern biochemical gradients into a range of biomaterial systems. Gradients of bone morphogenetic protein 2 in agarose hydrogels were used to spatially direct the osteogenesis of human mesenchymal stem cells and generate robust osteochondral tissue constructs exhibiting a clear mineral transition from bone to cartilage. Interestingly, the smooth gradients in growth factor concentration gave rise to biologically-relevant, emergent structural features, including a tidemark transition demarcating mineralized and non-mineralized tissue and an osteochondral interface rich in hypertrophic chondrocytes. This platform technology offers great versatility and provides an exciting new opportunity for overcoming a range of interfacial tissue engineering challenges.

High magnetostriction with low saturation field in highly 〈0 0 1〉 textured CoFe2O4 by magnetic field alignment

We report the magnetostriction and 〈0 0 1〉 texture of anisotropic polycrystalline CoFe2O4. Slurries with well dispersion and low sintering shrinkage are aligned by the magnetic field of 2 T and sintered to prepare highly 〈0 0 1〉 textured CoFe2O4 samples. For the anisotropic sample, benefiting from the 〈0 0 1〉 fiber texture, a higher magnetostrictive property is achieved than that of isotropic polycrystalline sample prepared by dry compaction. The maximum magnetostriction up to −500 ppm at 1000 Oe is obtained, which reaches 85% of the highest value in single crystal (λ100 = −590 ppm). Meanwhile, the maximum strain-field derivative is also improved to −0.97 ppm/Oe at 250 Oe, which is highly beneficial for sonar detector and force sensor applications.

Numerical modelling of inverse wire array Z-pinch magnetic reconnection

In this paper, a relaxation magnetohydrodynamic model is used to study magnetic reconnection phenomena in pulsed-power-driven Z-pinch inverse wire arrays. We focus on certain characteristics of two distinct modes that differ by resistivity. A magnetic field alignment that is both anti-parallel and open is created in high-resistivity mode. This produces a pronounced slow/standing shock wave and outflows can be accelerated to super-magnetosonic velocities. In low-resistivity mode, the entire magnetic field is closed and there is no pronounced slow/standing shock wave. The outflow velocity along the neutral line is accelerated to magnetosonic velocities between the two magnetic islands, but slows afterwards. It is difficult to achieve steady or quasi-steady magnetic reconnection in pulsed-power-driven Z-pinch inverse wire arrays.

Low magnetic field-induced alignment of nickel particles in segregated poly(l-lactide)/poly(ε-caprolactone)/multi-walled carbon nanotube nanocomposites: Towards remarkable and tunable conductive anisotropy

Anisotropic conductive composites with segregated conductive networks were constructed in poly(l-lactide)/poly(ε-caprolactone)/multi-walled carbon nanotubes/nickel (PLLA/PCL/MWCNT/Ni) composites by aligning Ni particles using a low magnetic field. Firstly, MWCNTs were melt-mixed with PLLA to form PLLA/MWCNT composites and then pulverized into microscale PLLA/MWCNT particles 425–850 μm in size. Later, the Ni particles were dispersed in PCL to yield PCL/Ni composites and then mixed with PLLA/MWCNT particles at 100 °C, a temperature lying in between the melting temperatures of PCL and PLLA. The coated PLLA/MWCNT particles were compressed to form PLLA/PCL/MWCNTs/Ni composites with segregated structures. A remarkable conductive anisotropy was observed in the segregated samples after magnetic alignment in a low magnetic field of ∼47.5 mT at 100 °C for 30 min. The electrical conductivity of the segregated samples diametrically increased in the direction parallel to the magnetic field, but decreased in the direction perpendicular to the magnetic field after the magnetic alignment of Ni particles in the PCL phase. Electrical conductivity in the parallel direction was almost eight orders of magnitude higher than that in the perpendicular direction at 3.0 wt% Ni and 0.7 wt% MWCNTs. Conductive anisotropy in the segregated systems could also be easily regulated by controlling the treatment time or changing the direction of the magnetic field. However, electrical conductivity could be maintained in both vertical and parallel directions in conventional composites after magnetic treatment because Ni particles preferably dispersed in the continuous PLLA phase, in which the Ni particles cannot be aligned at 100 °C. In addition, these segregated samples with alignment of Ni particles also exhibited the mechanical enhancement and high-performance electromagnetic interference shielding.

Effect of the aligned magnetic field on the boundary layer analysis of magnetic-nanofluid over a semi-infinite vertical plate with ferrous nanoparticles

PurposeThe purpose of this paper is to investigate the momentum, heat and mass transfer characteristics of magnetic-nanofluid flow past a vertical plate embedded in a porous medium filled with ferrous nanoparticles. The analysis is carried out in the presence of pertinent physical parameters such as aligned magnetic field, thermal radiation, chemical reaction, radiation absorption, heat source/sink.Design/methodology/approachThe flow governing PDEs are transformed into ODEs using appropriate conversions. Further, the set of ODEs is solved analytically using the perturbation technique. The flow quantities such as velocity, thermal and concentration fields are discussed under the influence of above-mentioned pertinent physical parameters with the assistance of graphical depictions. Moreover, the friction factor, local Nusselt and Sherwood number are discussed in tabular form.FindingsThe results indicate that flow and thermal transport phenomenon is more effective in the case of the aligned magnetic field as compared with the transverse magnetic field. Also, the nanoparticle volume fraction plays a vital role in controlling the wall friction and heat transfer performance. The validation of the obtained results is done by comparing them with the results of various numerical techniques, and hence found them in excellent agreement.Originality/valueIn present days, the external magnetic fields are very effective to set the thermal and physical properties of magnetic-nanofluids and regulate the flow and heat transfer characteristics. The strength of the applied magnetic field affects the thermal conductivity of magnetic-nanofluids and makes it aeolotropic. With this incentive, the authors investigated the flow and heat transfer characteristics of electrically conducting magnetic-nanofluids over a vertical surface embedded in a porous medium. The authors discussed the dual nature of ferrous-water nanofluid in the presence of aligned magnetic field and transverse magnetic field cases. The influence of several physical parameters on velocity, thermal and concentration field converses with the succour of graphs.

Low-Field Nuclear Polarization Using Nitrogen Vacancy Centers in Diamonds.

It was recently demonstrated that bulk nuclear polarization can be obtained using nitrogen vacancy (NV) color centers in diamonds, even at ambient conditions. This is based on the optical polarization of the NV electron spin, and using several polarization transfer methods. One such method is the nuclear orientation via electron spin locking (NOVEL) sequence, where a spin-locked sequence is applied on the NV spin, with a microwave power equal to the nuclear precession frequency. This was performed at relatively high fields, to allow for both polarization transfer and noise decoupling. As a result, this scheme requires accurate magnetic field alignment in order preserve the NV properties. Such a requirement may be undesired or impractical in many practical scenarios. Here we present a new sequence, termed the refocused NOVEL, which can be used for polarization transfer (and detection) even at low fields. Numerical simulations are performed, taking into account both the spin Hamiltonian and spin decoherence, and we show that, under realistic parameters, it can outperform the NOVEL sequence.

A novel method for imitating nacre by utilizing magnetic graphene oxide and its magnetic field alignment in polymer nanocomposites

The way gas molecules penetrate the resin matrix composites are generally divided into diffusion penetration and destruction penetration. Through theoretical analysis, the larger the nanoscale layers, the smaller the penetration effect in the directional nanosheets reinforced resin matrix composites. To control destruction penetration, the cracks should be reduced by toughening resin matrix composites. In order to solve these two kinds of leakage, the magnetic graphene oxide is connected to mimic nacre while L- glutamic acid is used as binder and the directional solidification is also utilized. Compared with pure resin, only 0.13 wt% monolithic magnetic graphene oxide and its interbed reinforced composites can reduce the leakage of He by 36.4% and 52.0% respectively, and the toughness of composites is validated to increase 4.0% and 20.3% respectively. This toughening mechanism is similar to that of nacre.

Effect of High Magnetic Pulse Iteration on Electrical Property of CNT-Polypyrrole Composite: Alignment Mechanism

In this work, a pulsed magnetic field of 10 T with a duration of 1.5 ms is produced by a resistor-inductor-capacitor (RLC) discharge system. A carbon nanotube-polypyrrole (CNT-PPy) composite (9 wt%) is prepared. The influence of the pulsed magnetic field iteration on the alignment of CNTs embedded in polymer matrix is observed (up to 60 pulses). The microstructure of the magnetically aligned composites is probed by scanning probe microscopy technique. The behavior of a CNT in a magnetic field is theoretically studied, and the equivalent magnetic susceptibility for an anisotropic CNT is calculated. The theory of CNT alignment in a magnetic field is discussed. We found that the perpendicular diamagnetism of a CNT results in its alignment in a magnetic field. We showed that the magnetic torque, which is applied to a CNT, depends on the perpendicular and parallel susceptibilities of the CNT as well as on its initial orientation with respect to the magnetic direction. After exposure to magnetic pulses, the electrical property of the composites is enhanced. The results show that there is a positive correlation between the electrical conductance of CNTs and the number of applied pulses (for 30 pulses). Fourier transform infrared spectroscopy technique is used to control the polymer structure during the experiment. Our theoretical finding reveals the limited capacity of CNT’s alignment in magnetic fields.

Giant magnetocaloric effect in composites based on polymeric matrix and manganese arsenide

A field and/or temperature hysteresis is more than just an interesting incomprehensibility that occurs in materials with a first-order magnetic transition. Indeed, the reversibility of the magnetocaloric effect (MCE), being essential for magnetic heat pumps, strongly depends on the width of the thermal hysteresis and, therefore, it is necessary to find solutions to minimize losses associated with thermal hysteresis in order to maximize the efficiency of magnetic cooling devices. In this work, the polymer matrix composites with MnAs powder as reinforcing material were obtained and its MCE by direct method was studied. The influence of composite preparation process on the MCE was investigated. It was found that the MCE of bulk MnAs shows strong temperature hysteresis caused by magnetostructural transition from paramagnetic to ferromagnetic state, which also leads to an irreversible MCE at cooling at first magnetization. The reversible MCE of bulk MnAs in field 12.5 kOe is ΔT ∼ 0.4 K. It was shown that Mn-based polymeric composite cured in aligned magnetic field presents a reinforcement of the MCE temperature hysteresis. Thus, the MCE value in aligned composite is less than the value of the MCE in the bulk MnAs. It was shown that the decreasing of linear size of MnAs grains in the polymeric composite leads to sharp decreasing of the MCE to value of 0.05 K. It was established that the optimal properties, such as giant MCE and low temperature hysteresis, are found for composite hardened under pressure of 10 kBar. In this composite an increase of reversible MCE (compared to the bulk MnAs) till to the value of ΔT ∼ 1.2K was observed.

Flow and heat transfer of aligned magnetic field with Newtonian heating boundary condition

Influence of aligned magnetic field on the steady boundary layer flow and heat transfer over a stretching sheet with Newtonian heating boundary condition is considered. The transformed governing nonlinear boundary layer equations in the form of ordinary differential equations are solved numerically by Keller box method. The details on computation have been presented and elaborated. The obtained numerical solutions have been captured graphically in the form of velocity and temperature distributions for different values of aligned angle, magnetic field parameter, Prandtl number and conjugate parameter. It is found that, increases in aligned angle associated with magnetic field delayed the velocity profile of the flow and enhances the temperature profile.

Aligned magnetic field effect on unsteady liquid film flow of Casson fluid over a stretching surface

The heat and mass transfer in non-Newtonian fluids plays a major role in technology and in nature due to its stress relaxation, shear thinning and thickening properties. In this study, we investigated the heat and mass transfer in unsteady liquid film flow of Casson fluid in the presence of aligned magnetic field, thermophoresis and Brownian moment effects. The transformed governing boundary layer equations are solved numerically by employing shooting technique. Dual solutions are explored for Newtonian and non-Newtonian cases. The impact of pertinent parameters on the flow, thermal and concentration fields are discussed with the assistance of graphical illustrations. The reduced Nusselt number is reported and discussed through tabular results.

Dual solutions of cross diffusion effects on MHD Peristaltic flow in a conduit

The purpose of this study is to analyze the influence of wall flexibility and cross diffusion on the peristaltic transport of a MHD dissipative fluid in uniform channel in the presence of Joule heating. Dual solutions are obtained for aligned and transverse magnetic field cases. The exact solution is obtained for stream function and velocity. Further, shooting process is employed to solve the energy and concentration equations. The influence of main parameters on the present flow is explained graphically. The increase in magnetic field decreases the velocity of the fluid. Also Dufour and Soret numbers enhances the temperature while they reduses the concentration field.

Numerical study on slip effects on aligned magnetic field flow over a permeable stretching surface with thermal radiation and viscous dissipation

This work concentrates on the study of the unsteady hydromagnetic heat and mass transfer of a Newtonian fluid in a permeable stretching surface with viscous dissipation and chemical reaction. Thermal radiation, velocity slip, concentrate slip are also considered. The unsteady in the flow, velocity, temperature and concentration distribution is past by the time dependence of stretching velocity surface temperature and surface concentration. Appropriate similarity transformations are used to convert the governing partial differential equations into a system of coupled non-linear differential equations. The resulting coupled non-linear differential equations are solved numerically by using the fourth order Runge-Kutta method along with shooting technique. The impact of various pertinent parameters on velocity, temperature, concentration, skin friction coefficient, Nusselt number and the Sherwood number are presented graphically and in tabular form. Our computations disclose that fluid temperature has inverse relationship with the radiation parameter.