Effect Of High Magnetic Field Research Articles

Atomic resolution electron microscopy in a magnetic field free environment

Atomic-resolution electron microscopes utilize high-power magnetic lenses to produce magnified images of the atomic details of matter. Doing so involves placing samples inside the magnetic objective lens, where magnetic fields of up to a few tesla are always exerted. This can largely alter, or even destroy, the magnetic and physical structures of interest. Here, we describe a newly developed magnetic objective lens system that realizes a magnetic field free environment at the sample position. Combined with a higher-order aberration corrector, we achieve direct, atom-resolved imaging with sub-Å spatial resolution with a residual magnetic field of less than 0.2 mT at the sample position. This capability enables direct atom-resolved imaging of magnetic materials such as silicon steels. Removing the need to subject samples to high magnetic field environments enables a new stage in atomic resolution electron microscopy that realizes direct, atomic-level observation of samples without unwanted high magnetic field effects.

Safety of exposure to high static magnetic fields (2T-12T): a study on mice.

We aimed to evaluate the biological effects of high static magnetic field (HiSMF, 2-12Tesla [T]) exposure on mice in a stable and effective breeding environment in the chamber of a superconducting magnet. C57BL/6 mice were bred in the geomagnetic field and HiSMF with different magnetic field strengths (2-4T, 6-8T, and 10-12T) for 28days. The body weight, blood indices, organ coefficients, and histomorphology of major organs were analyzed. The results showed that the HiSMF had no significant effect on the body weight, organ coefficients, or histomorphology of major organs in mice. The HiSMF had no effect on most routine blood and biochemical indices, but the value of the mean corpuscular hemoglobin (MCH) was increased in the 2-4T group compared with that of the other groups, and the uric acid level (UA) was decreased in the three HiSMF groups compared with that of the control group. The C57BL/6 mice were not affected when they were exposed to different HiSMF environments for 28days. • No physiological problems were observed in mice with long-term whole-body exposure to HiSMF.

Evolutions of microstructure and magnetic property of wet-chemical synthesized FePt nanoparticles assisted by high magnetic field

A high magnetic field up to 6 T was introduced into the wet-chemical process to synthesize FePt nanoparticles. The effects of high magnetic field on the composition, crystal structure, shape, size and magnetic property of FePt nanoparticles were studied. Under the high magnetic fields, the grain size of FePt nanoparticles refined, and the shape transformed from cube to truncated-cube and concave-cube to cube. However, the high magnetic fields show no significance effects on the composition and crystal structure of FePt nanoparticles. As a result, the magnetic properties of FePt nanoparticles were tuned by high magnetic fields. The coercivity at low-temperature (10 K) and the blocking temperature both decreased at 6 T. The results highlight the feasibility of applying an in-situ high magnetic fields to tune magnetic properties of the wet-chemical synthesized nanoparticles.

Shape oscillation of a sessile drop under the effect of high frequency amplitude-modulated magnetic field

The shape oscillation behavior of a sessile mercury drop under the effect of high frequency amplitude-modulated magnetic field (AMMF) is investigated experimentally. It is an effective method to excite the shape oscillation of a liquid metal sessile drop. The high frequency AMMF is generated by a solenoid inductor fed by a specially designed alternating electric current. The surface contour of the sessile drop is observed by a digital camera. At a given modulation frequency and magnetic flux density of the high frequency AMMF, the edge deformations of the drop with azimuthal wave numbers (modes n = 2, 3, 4, 5, 6) were excited. A stability diagram of the shape oscillation of the drop is obtained by analysis of the experimental data. It turns out that when the modulation frequency and magnetic flux density reach a point in the stability diagram which can trigger shape oscillations of the drop of several modes, the shape oscillation of different modes may be seen alternatively.

Porphyrin-Based Triad with Exceptionally High Magnetic Field Effects (MFE) on Phosphorescence

Magnetic control over molecular emissivity presents interests for various fields of technology and medicine. Here, we report experiments exploring magnetic field effects (MFE) on phosphorescence in a new triad, consisting of phosphorescent Pt porphyrin (PtP), rosamine B (RosB) and trialkoxybenzene (TAB), covalently linked together by conductive oligophenylene bridges. Upon photoexcitation the system undergoes two sequential reversible electron transfer processes (ET), generating two radical pairs (RP). The first rate-limiting ET originates in the local PtP triplet state, and it is slightly endergonic, competing with, but not entirely quenching the PtP phosphorescence. The second ET is exergonic, resulting in the formation of the final RP with large inter-radial distance. The RPs recombine either to the ground state (singlet channel) or back to the emissive PtP triplet state (triplet channel). The net distribution over the recombination channels, and hence the phosphorescence decay lifetime and intensity, are governed by the spin dynamics in the RP(s) and, therefore, are sensitive to external magnetic fields. The triad was found to exhibit remarkably strong positive MFE on phosphorescence at ambient temperatures with the magnitude of ~10% in fields as low as 200 mT. The observed features are characteristic of the hyperfine mechanism, although at higher fields a slight negative MFE was also observed, presumably due to the Δg mechanism. The system was characterized by static and time-resolved optical spectroscopies in the fs, ns and μs-to-ms domains as well as by time-resolved EPR. These studies revealed peculiar dynamics of the system, whereby the initial population of the PtP triplet rapidly equilibrates with the RosB triplet, forming a long-lived triplet reservoir, existing in equilibrium with the RP states. A kinetic model has been developed that allowed us to accurately reproduce the observed charge and energy dynamics of the triad. The model makes it possible to predict how the MFE and the performance of the system can be improved. Overall, this work constitutes an important step forward towards the design of magnetically sensitive luminescent materials.

The effect of high magnetic field on the microstructure evolution of a Cu-Co alloy during non-equilibrium solidification

The effects of high magnetic field on the microstructure evolution of non-equilibrium solidified Cu80Co20 alloy have been investigated by glass fluxing combined with cyclic superheating and cooling method in a superconducting magnet. Results show that both the undercooling and magnetic field can affect the microstructure of Cu80Co20 alloy. The size of Co-rich phase increases with the enlarged undercooling. The Co-rich particles are elongated along the direction of 6 T magnetic field while these granules become more dispersed perpendicular to the direction of 6 T magnetic field. Moreover, the volume fraction of Co-rich phases perpendicular to the 6 T magnetic field reduces significantly.

Effect of an axial high static magnetic field on the crystal orientation and magnetic property of Fe-4.5 wt% Si alloy during bulk solidification

Fe-4.5 wt% Si alloy was solidified in the presence of an axial high static magnetic field (HSMF) to investigate the influence of magnetic field on the crystal orientation and magnetic property. With the increase of magnetic field intensity (MFI), the crystal orientation of the Fe-4.5 wt% Si alloy turns to 〈1 0 0〉 which is the easy magnetization axis. The specimen with strong Goss texture was obtained under a 6 T HSMF. Moreover, the saturation magnetic induction also increases with the increase of the MFI. The above results are attributed to the effect of the HSMF on the magnetocrystalline anisotropy during bulk solidification.

Three dimensional dendritic morphology and orientation transition induced by high static magnetic field in directionally solidified Al-10 wt.%Zn alloy

Effect of high static magnetic field on the dendritic morphology and growth direction in directionally solidified Al-10 wt.%Zn alloy were studied by three-dimensional (3D) X-ray micro-computed tomography, Electron Back-scattered Diffraction (EBSD) and X-ray Diffraction (XRD). The application of high static axial magnetic field (5T) during directional solidification was found to destabilize the solid/liquid interface and cause the growth direction of dendrite deviate from thermal gradient, leading to irregular solid/liquid interfacial shape and cellular to dendritic morphology transition. The thermoelectric magnetic convection (TEMC) caused by the interaction of thermoelectric effect and magnetic field was supposed to be responsible for the transition. In addition, the EBSD and XRD results confirm that the preferred growth direction of α-Al was found to transform from the traditionally expected <100> to <110>. The dendrite orientation transition (DOT) in Al-10 wt.%Zn alloy can be attributed to the effect of applied magnetic field on the anisotropy of crystal during solidification. The result indicates the potential application of high static magnetic field in altering the morphology and preferred growth direction of dendrite during directional solidification.

Effects of High Magnetic Fields on Phase Transformations in Amorphous Nd2Fe14B

We briefly summarize the results from a set of experiments designed to demonstrate the effects of high magnetic fields applied during thermal annealing of amorphous Nd2Fe14B produced through melt-spinning. A custom-built differential scanning calorimeter was used to determine the crystallization temperatures in zero-field and in applied fields of 20 kOe and 90 kOe, which guided subsequent heat treatments to evaluate phase evolution. X-ray diffraction was used for phase identification and transmission electron microscopy was employed for observation of the crystallite size and morphology. Magnetization measurements were also used to evaluate the resulting magnetic phases after thermomagnetic processing. While the applied magnetic fields do not appear to affect the crystallization temperature, significant effects on the kinetics of phase evolution are observed and correlated strongly to the magnetic behavior.

Effects of High Magnetic Field on the Energy Spectra of Two Donors in a Strained Zinc Blende Quantum Dot

Effects of High Magnetic Field on the Energy Spectra of Two Donors in a Strained Zinc Blende Quantum Dot

Effects of sintering in a high magnetic field on properties of vitrified bond and vitrified CBN composites

Vitrified bond CBN grinding wheels are being widely used due to their superior performance. Also, advantages of vitrified grinding wheels are high elastic modulus, stable chemical property, and low thermal expansion coefficient. Brittleness and low strength are key factors restricting the development of vitrified bond CBN grinding wheels. In this paper, the sintering in a high magnetic field was innovatively introduced into the manufacturing of vitrified bond CBN grinding wheels, and the effects of sintering in a high magnetic field on properties on vitrified bond and vitrified CBN composites were systematically investigated. Vitrified bond was characterized using three-point bending, scanning electron microscopy, X-ray diffraction. It was observed that microstructure of vitrified bond could be changed, grain orientation could be controlled and average grain size could be decreased in a high magnetic field, while vitrified bond strength could be simultaneously improved. High quality vitrified bond could be obtained by appropriately adjusting the strength and direction of high magnetic field. Results demonstrated that vitrified bond properties were improved when the magnetic field strength was 6 T. In order to highlight the high magnetic field effect on the vitrified CBN composites, the ordinary CBN abrasives and nickel plated CBN abrasives were used respectively. Microstructures, bending strengths of vitrified CBN composites were compared in different high magnetic fields. When the magnetic field strength was appropriate (less than 6 T), the binding characteristic of vitrified bond CBN composites with nickel plated CBN abrasives was greatly improved. The highest bending strength value of vitrified CBN composites was 79.5 MPa in 6 T high magnetic field.

Fabrication and magnetic properties of hexagonal BaFe12O19 ferrite obtained by magnetic-field-assisted hydrothermal process

High magnetic field effects on the microstructure and magnetic properties of BaFe12O19 hexaferrites synthesized hydrothermal method have been investigated. The obtained results indicate that the lattice constant decreases gradually as the magnetic field strength increases, which may be attributed to the lattice distortion resulted from the high magnetic field. Polycrystalline BaFe12O19 samples prepared under magnetic field strength at zero and 5 T are single phase. It is found that application of external magnetic field during synthesis can induce orientated growth of the hexaferrite crystals along the easy magnetic axis. The magnetic properties can be effectively regulated by an application of high magnetic fields. It is observed that the BaFe12O19 prepared under a 5 T magnetic field exhibits a higher room-temperature saturation magnetization (66.3 emu/g) than that of the sample (43.6 emu/g) obtained without magnetic field. The results can be explained as the enhanced crystalline, improvement of Fe3+ ions occupancy and the oriented growth induced by the external magnetic field. The growing orientation of particles gives rise to increased coercivity due to the enhancement in shape anisotropy. It is expected that an application of magnetic field during the formation of magnetic nanoparticles could be a promising technique to modify magnetic properties with excellent performance.

Effect of Magnetic state of Austenite on Martensitic transformation in Fe–Ni Alloys in High and Zero Magnetic Fields

The effect of high pulsed magnetic fields on the martensitic γ → α transformation in Fe–Ni and Fe–Ni–Mn alloys characterized by dual kinetics has been analyzed. It has been shown that the higher the iron content and the lower the martensitic transformation temperature, the more substantial the effect of pulsed magnetic field on the athermal martensitic transformation (MT) in the Fe–Ni alloys. The possibility of athermal martensite nucleation at magnetic inhomogenities of austenite, which is characterized by disordered magnetic moments (antiferromagnetic contribution) within a local area that assumes coherent conjugation at the interface, has been discussed. It has been suggested that athermal MT in Invar Fe–Ni alloys characterized by dual kinetics occurs in a pulsed magnetic field via a first-order magnetic phase transformation.

High magnetic-field-induced solute interception among dendrite arms in the mushy zone of a Mn–Sb alloy

The effect of high magnetic fields on the solute diffusion behavior in the mushy zone of a Mn–Sb alloy has been investigated. A hypoeutectic Mn–Sb alloy was heated in high magnetic fields to yield a mixture of primary MnSb dendrites and Mn/Sb liquid to simulate the mushy state, annealed isothermally for various times, and quenched to room temperature. Without a magnetic field or with a 1-T field, the quenched alloy had a microstructure that was composed of MnSb particles that were dispersed in MnSb/Sb eutectics. At higher magnetic fields, a multiple-phase mixed microstructure that consisted of fine MnSb particles, bulk Sb, and MnSb dendrites and eutectic was observed at relatively short annealing times. The amounts of fine MnSb particles and bulk Sb decreased with an increase in annealing time but increased with an increase in magnetic-flux density. The appearance of the multiple-phase mixed microstructure can be attributed to solute interception in the mushy zone, which can change the solute distribution among the dendrite arms and which is caused by a high magnetic field that is based on the Lorentz force. The application of a high magnetic field to the mushy state of the alloys is proposed as an effective route for the in-situ control of solute diffusion in the mushy zone.

Columnar growth structure dependent soft magnetic and electrical transport properties of Co nanocrystalline films evaporated with a high magnetic field

Control and improvement of the magnetic and electrical properties of magnetic nanocrystalline films are very essential for their applications in spintronics and magnetic storages. This paper studies the effects of high magnetic field (HMF) on the microstructure, soft magnetic and electrical transport properties of the Co nanocrystalline films. It was found that the Co films without HMF were disordered stack of spherical nanoparticles. The stack changed to columnar structure with the HMF application. Furthermore, this columnar crystal changed to columnar stack of spherical nanoparticles with the increase of evaporation temperature under HMF. HMF induced a part of the c-axis preferred orientation in the Co films aligning along the direction of HMF. The varied growth structure and preferred orientation led to the change from the in-plane magnetic anisotropy (without HMF) to isotropy in the Co films due to the application of HMF at a higher evaporation temperature. The saturation magnetization of the Co films with columnar crystals obtained by HMF was much larger than that of the films composed of spherical nanoparticles because of the dense atom arrangement. The decrease of the grain boundaries due to the changed growth structure under HMF remarkably reduced the coercivity and resistivity of the Co films. The changed growth structure under HMF also induced and improved the in-plane anisotropic magnetoresistance of the Co films. These results indicate that the adjustment of columnar growth structure by HMF effectively control and improve the soft magnetic and electrical transport properties of the Co films.

Effects of large gradient high magnetic field (LG-HMF) on the long-term culture of aquatic organisms: Planarians example.

Large gradient high magnetic field (LG-HMF) is a powerful tool to study the effects of altered gravity on organisms. In our study, a platform for the long-term culture of aquatic organisms was designed based on a special superconducting magnet with an LG-HMF, which can provide three apparent gravity levels (µ g, 1 g, and 2 g), along with a control condition on the ground. Planarians, Dugesia japonica, were head-amputated and cultured for 5 days in a platform for head reconstruction. After planarian head regeneration, all samples were taken out from the superconducting magnet for a behavioral test under geomagnetic field and normal gravity conditions. To analyze differences among the four groups, four aspects of the planarians were considered, including head regeneration rate, phototaxis response, locomotor velocity, and righting behavior. Data showed that there was no significant difference in the planarian head regeneration rate under simulated altered gravity. According to statistical analysis of the behavioral test, all of the groups had normal functioning of the phototaxis response, while the planarians that underwent head reconstruction under the microgravity environment had significantly slower locomotor velocity and spent more time in righting behavior. Furthermore, histological staining and immunohistochemistry results helped us reveal that the locomotor system of planarians was affected by the simulated microgravity environment. We further demonstrated that the circular muscle of the planarians was weakened (hematoxylin and eosin staining), and the epithelial cilia of the planarians were reduced (anti-acetylated tubulin staining) under the simulated microgravity environment. Bioelectromagnetics. 2018;39:428-440. © 2018 Wiley Periodicals, Inc.

Effect of High Magnetic Field on the Growth, Magnetic, and Electrical Properties of Nanocrystalline Ni Films with Different Thicknesses and Growth Rates

To realize the application of Ni films in magnetic recording media, giant magnetoresistive sensors and microelectromechanical systems, it is necessary to control and improve the magnetic and electrical properties of the films. In this paper, Ni nanocrystalline films with different thicknesses and growth rates are prepared with or without a high magnetic field (HMF). The effects of a HMF on the growth, magnetic and electrical properties of the Ni films are studied. The results show that HMF changes the growth structure of the Ni films from disordered stacked grains to columnar growth along the direction of the HMF. The columnar growth becomes more prominent at a high growth rate and large film thickness. The HMF increases the grain size but decreases the surface roughness of the Ni films. Due to changes in the growth structure, grain size and film quality, the saturation magnetization of the Ni films increase markedly (by 89%), and the resistivity and coercivity significantly decrease (by 89 and 58%, respectively) by the HMF. The remanence ratio of the Ni films is controlled by the HMF. This study shows that a HMF effectively controls the growth and improves the magnetic and electrical properties of Ni films.

The possible effect of high magnetic fields on the aqueous corrosion behaviour of Eurofer

In defining the corrosion control requirements for DEMO, the impact of the mixed Eurofer-97/AISI 316 steel system and plant specific effects should be considered throughout, in particular, the effect of the intense magnetic fields present. A substantial amount of data related to corrosion resistance of structural materials is available for industrial applications in fission, but applies to different materials and neutronic conditions. Experimental work is being carried out under the DEMO Breeding Blanket Project of the EUROfusion programme, which will further develop the understanding of irradiation effects. However, there is very limited information regarding magnetic field-assisted corrosion under conditions relevant for the fusion environment readily available in the literature. This work reviews current knowledge and progress in establishing the possible influence of the intense magnetic field on corrosion behaviour of the main structural material, Eurofer-97, in the breeding blanket. To support the relevance of this problem statement, preliminary corrosion experimental results of Eurofer-97 coupons, obtained by using a simple apparatus that allows exposure to a magnetic field intensity of 0.88 T and temperatures up to 80 °C in water at atmospheric pressure, are presented as an initial qualitative investigation of possible magnetic field related effects.

Effect of high magnetic field on the pearlite transformation of Al-containing steel

ABSTRACTComparative studies were carried out on the effect of high magnetic field on the pearlite transformation of Al-containing high carbon steels under the furnace slow cooling condition. For 1.37Al-bearing high carbon steel, the amount of pearlite was only 6 ± 3 vol.-% without magnetic field, whereas full pearlite was obtained under a 12-T high magnetic field. For free-Al high carbon steel, no pearlite transformation occurred, whereas lots of bainite were formed under a 12-T high magnetic field. In addition, the interlamellar spacing of pearlite increased from 100 ± 7 to 112 ± 18 nm by the application of a 12-T magnetic field. It has been proved that the pearlite transformation of high carbon steel was promoted by high magnetic field and by the addition of aluminium.This is part of a thematic issue on Pearlitic Steel Wires.

Effect of high static magnetic field on the microstructure and mechanical properties of directionally solidified alloy 2024

The commercial alloy 2024 was directionally solidified under different magnetic fields and its microstructure and tensile mechanical properties were investigated. The application of magnetic field during solidification and the following heat treatment were demonstrated to improve the tensile strength and elongation properties of alloy 2024. This is because the formation of microstructure during solidification and the distribution of secondary phase after heat treatment were alternated by the magnetic field. It was found that the primary dendrite arm spacing decreases first and then increases with the magnetic field raising. The result is ascribed to the influence of magnetic field on the fluid flow during solidification. In addition, the effect of high static magnetic field on the secondary phase fraction was also studied in both as-cast and heat treatment samples, the fraction of secondary phase increased in the sample solidified under magnetic field. However, after T6 heat treatment, more secondary phase was dissolved into the α-Al matrix due to the magnetic damping effect on the solute distribution during solidification process.