Pulsed High Magnetic Fields Research Articles

Function Design and Implementation of a Central Control System of a Pulsed High Magnetic Field Facility

A user-friendly Central Control System (CCS) for the pulsed high magnetic field facility has been designed and implemented at the Wuhan National High Magnetic Field Center (WHMFC). The CCS is composed of the server, the Human Machine Interface (HMI) and the configuration tool. The controlled objects and functions of the CCS are introduced first, and then the design and implementation of key functions are given. The CCS is developed on basis of a client/server mode, so multiple users can use the system simultaneously. To achieve higher pulsed magnetic fields, a synchronous trigger sequence is used, which can trigger up to 13 power modules to be discharged into a magnet with multiple coils. Benefiting from component technology and the TCP/IP communication protocol, the CCS can monitor signals in real time and receive experimental data from recording devices running on different platforms. The test results show that the CCS meets the requirements of experiments and simplifies the control operation.

Design of a Program-Controlled Precise Synchronous Triggering System Applied to Pulsed High Magnetic Field Facility

Recently, a Program-controlled Synchronous Triggering System (PSTS) is developed at Wuhan National High Magnetic Field Center. The designed system could generate triggering signal for thirteen power modules and eight magnets distributed in different experiment stations. By generating precise and synchronous triggering signals required for the facility, the multiple power modules could be discharged synchronously or in a preset time sequence. The PSTS is composed of triggering signal generator, fiber converter, expanded cell, and local sequence generator. The triggering signal generator, isolated from local device, is applied for sequential control of multi-module in the facility. The signal transmission is realized by optical fiber. A Digital Signal Processor (DSP) with specific type of TMS320F2812 is employed to design the triggering signal generator. The parameters of triggering channels and time-delay with the accuracy of 1 us could be configured through human machine interface. Local sequence generator unit is integrated in the local control unit on the basis of a Complex Programmable Logic Device (CPLD) with specific type of EPM7128. Local sequence generator is responsible for producing the time sequence signals to control and record the waveform of each power module, as well as the triggering signal waveform modulation for thyristor through expanded cell. Based on the designed system, the pulsed high magnetic field facility could be operated effectively. The test result illustrates that the system is of high performance.

Multiferroicity on the Zigzag-Chain Antiferromagnet MnWO4 in High Magnetic Fields

The electric polarization and magnetization of the zigzag-chain antiferromagnet MnWO 4 were measured in high pulsed magnetic fields of up to 53 T for the three principal directions x , y , and z , where x corresponds to the easy axis and y is the b * -direction. In addition to the AF1, AF2, and HF phases already known, two magnetic phases, IV and V, successively appear in high magnetic fields for B ∥ x at 4.2 K. We found that phase IV is ferroelectric with the electric polarization P parallel to the b * -axis, similar to the AF2 phase. It is also confirmed that phase IV is continuously connected to the previously reported X phase for the B ∥ y axis by changing the field direction. Interestingly, the successive field-induced phase transitions AF2–HF–IV in B ∥ x at a low temperature revealed that the signs of P ∥ b * for AF2 and phase IV are always opposite each other, in spite of the intervening paraelectric HF phase extending to over 20 T. This result implies that an unusual memory effect is present in th...

Optical imaging and magnetocaloric effect measurements in pulsed high magnetic fields and their application to Ni–Co–Mn–In Heusler alloy

► High-speed imaging system in pulsed magnetic field was developed. ► The phase diagram of Ni 45 Co 5 Mn 36.7 Al 13.3 was determined by the optical images. ► Magneto-caloric effect measurement system in pulsed magnetic field was developed. ► Magneto-caloric effect of Gd was consistent with the estimation from specific heat. ► Gigantic adiabatic heating larger than 60 K in Gd was observed. As novel tools to study magnetic shape memory alloys, a high-speed optical microscope system and a measurement system of magnetocaloric effects (MCEs) in pulsed magnetic fields are developed. Using the high-speed imaging system, successive changes in the surface morphology are visualized in the process of magnetic field-induced reverse martensitic transformation in Ni 45 Co 5 Mn 36.7 In 13.3 . The MCEs of Gd studied in pulsed fields show reasonable agreement with the earlier results obtained in steady fields. Application of high magnetic fields up to 55 T realizes a gigantic adiabatic heating of 63 K.

Effect of pulse magnetic field stimulation on calcium channel current

This study aimed to investigate the effect of low frequency and high amplitude pulse magnetic field (PMF) on Calcium ion channel current of cells. Measurements were done on the Human Embryonic Kidney 293 cells (HEK 293), which have only Calcium ion channels functioning. The whole cell current was measured by patch clamp method, with the clamped voltage ramping from −90mV to +50mV across the cell membrane. A PMF was generated by a 400-turn coil connected to a pulse current generator. The frequency of the pulse was 7Hz, the width of the pulse was 3ms, and the amplitude of the pulse, or the flux density, was ranging from 6 to 25mT. The results showed that the profile of the whole cell Calcium channel current could be modified by the PMF. With the PMF applied, the phase shifting occurred: the onset of the channel opening took place several mili-seconds earlier than that without the PWF and correspondingly, the whole cell current reached its maximum earlier, and the current returned back to zero earlier as well. When the PWF was stopped, these effects persisted for a period of time, and then the current profile “recovered” to its original appearance. The decrease of the onset time and peak current time could be due to the local electric potential induced by the PWF and the direct interaction between PMF and ion channels/ions. The exact mechanisms of the observed effects of PMF on the cell are still unknown and need to be further studied.

Magnetic field-induced spin-crossover transition in [MnIII(taa)] studied by x-ray absorption spectroscopy

X-ray absorption near-edge structure (XANES) spectra of Mn in a spin-crossover compound, [MnIII(taa)], was studied in pulsed high magnetic fields up to 37 T. The significant changes in the XANES spectra, related to the spin-crossover from the low-spin (LS) state to high-spin (HS) state, were found to be induced by magnetic fields at temperatures down to 17 K. The fraction of the field-induced HS states was, at most, 30%, and the magnetic field dependence of the HS fraction exhibited hysteresis. The observed field-induced spin-crossover at T = 17 K (T/Tc ∼ 0.4, where Tc (= 46 K) is the spin-crossover transition temperature) cannot be understood as the field-induced macroscopic phase transition, because the transition magnetic field is known to be higher than 55 T at low temperatures. The observed field-induced LS-HS transition is likely the local microscopic transition at the single-molecule level.

Precise measurement of magnetization characteristics in high pulsed field

Permanent magnets, especially Nd-Fe-B magnets, are very important engineering elements that are widely used in many applications. The detailed design of electrical and electronic equipment using permanent magnets requires the precise measurement of magnetization characteristics. High pulsed magnetic fields can be used to measure the magnetization characteristics of permanent magnets in the easy and hard magnetization directions. Errors influencing the measurements stem from the relationship between the tested material, pick-up sensor configuration, and excitation coil. We present an analysis of the effect of the sensor construction on the accuracy of the measurements of the material’s magnetic properties. We investigated the coaxial and series types sensor configurations.

Spin‐flip transition and non‐one‐dimensional magnetic coupling in quasi‐one‐dimensional oxygen deficient Sr6Co5O15–δ

AbstractHigh‐quality single‐crystal Sr6Co5O15–δ (δ = 1.33) was successfully synthesized with a flux method. Detailed crystalline structure was determined by single‐crystal X‐ray diffraction at 298 K, which revealed a quasi‐one‐dimensional Co–O chain‐like structure of this oxygen‐deficient material. The magnetizations were measured in a pulsed high magnetic field up to 32 T and with a Physical Property Measurement System (PPMS). A large anisotropy and a distinct spin‐flip transition were observed in the magnetization behavior. Theoretical calculation based on Botana's results suggests that interchain interaction (non‐one‐dimensional magnetic coupling) plays an important role in the magnetic properties of Sr6Co5O15–δ.

A Magnetic Flux Leakage and Magnetostrictive Guided Wave Hybrid Transducer for Detecting Bridge Cables

Condition assessment of cables has gained considerable attention for the bridge safety. A magnetic flux leakage and magnetostrictive guided wave hybrid transducer is provided to inspect bridge cables. The similarities and differences between the two methods are investigated. The hybrid transducer for bridge cables consists of an aluminum framework, climbing modules, embedded magnetizers and a ribbon coil. The static axial magnetic field provided by the magnetizers meets the needs of the magnetic flux leakage testing and the magnetostrictive guided wave testing. The magnetizers also provide the attraction for the climbing modules. In the magnetic flux leakage testing for the free length of cable, the coil induces the axial leakage magnetic field. In the magnetostrictive guided wave testing for the anchorage zone, the coil provides a pulse high power variational magnetic field for generating guided waves; the coil induces the magnetic field variation for receiving guided waves. The experimental results show that the transducer with the corresponding inspection system could be applied to detect the broken wires in the free length and in the anchorage zone of bridge cables.

Development of a Two-Axis Rotator in Pulsed High Magnetic Fields for a Magnetic Torque Measurement

We present a magnetic torquemeter utilizing a piezoresistive microcantilever for use in pulsed high magnetic fields. Pulsed high magnetic fields are generated with a non-destructive pulsed magnet, which has a large bore diameter (48 mm) and a large sample space size (33 mm). Since differential gears are built into the sample space of this apparatus, it is possible to change sample angles against the magnetic field direction freely. By using this apparatus, we have performed the de Haas–van Alphen (dHvA) measurement on a high-quality Pb single crystal.

Observation of quantum Hall effect in mono- and bi-layer graphene using pulse magnet

We report on the magnetotransport measurements of mono- and bi-layer graphene in pulsed high magnetic fields up to B = 53 T. In a mono-layer graphene, the Hall resistance RH is quantized to RH = (h/e2)ν−1 with ν = 2, 6, and 10 for either hole or electron doping. In a bi-layer graphene, RH is quantized to RH = (h/e2)ν−1 with ν = 4, 8, and 12. These results indicate that the precise magnetotransport measurements of the graphene can be conducted in the environment of pulse magnetic fields.

Probing the anisotropy constants of SmCo5 and PrCo5 by Hall resistance measurements in pulsed high magnetic fields up to 47 T

In order to assess the anisotropy constants of highly anisotropic thin film samples with anisotropy fields well above 10T, Hall resistance measurements were conducted in pulsed magnetic fields. These measurements also deliver the anomalous Hall data, which are proportional to the perpendicular magnetisation. This specific approach combines the high field values obtainable by pulsed fields with a measurement technique sensitive enough to be applied to thin film samples. Two epitaxial Rare Earth-Cobalt thin films with large in-plane uniaxial magnetocrystalline anisotropy at room temperature were studied. The resulting anisotropy fields and constants are discussed with respect to measurements on single crystals and similar films investigated in quasi-static magnetic fields well below the anisotropy field. The present technique proved to be very valuable to highly anisotropic samples, as the approach to saturation is fully monitored and the data thus provides a more extended view on the hard axis magnetisation process.

Quantum vacuum magnetic birefringence

In this contribution to EXA2011 congress, we present the status of the BMV (Birefringence Magnetique du Vide) experiment which is based on the use of a state-of-the-art optical resonant cavity and high pulsed magnetic fields, and it is hosted by the Laboratoire National des Champs Magnetiques Intenses in Toulouse, France.

Enhancement of the upper critical field in codoped iron-arsenic high-temperature superconductors

We present the first study of codoped iron-arsenide superconductors of the 122 family (Sr/Ba)1-xKxFe2-yCoyAs2 with the purpose to increase the upper critical field Hc2 compared to single doped Sr/BaFe2As2 materials. Hc2 was investigated by measuring the magnetoresistance in high pulsed magnetic fields up to 64 T. We find, that Hc2 extrapolated to T=0 is indeed enhanced significantly to ≈ 90 T for polycrystalline samples of Ba0.55K0.45Fe1.95Co0.05As2 compared to ≈75 T for Ba0.55K0.45Fe2As2 and BaFe1.8Co0.2As2 single crystals. Codoping thus is a promising way for the systematic optimization of iron-arsenic based superconductors for magnetic-field and high-current applications.

19F NMR study of LiTbF4 single crystals

The angular dependences of 19F NMR spectra have been measured in the external magnetic field of 0.5 T oriented in the basis plane of LiTbF4 at the room temperature. We have obtained the constants of transferred hyperfine interaction and the corrected set of crystal field parameters for the Tb3+ ions in LiTbF4. The results of simulations of the magnetization in high pulsed magnetic fields with taking into account magnetoelastic interactions agree satisfactorily with experimental data presented in the literature.

PHELIX: Design and Analysis of a Transformer-Driven Liner Implosion System

To provide substantial reduction in the size and energy of high-energy-density experiments, we have designed, built, and operated a liner implosion system that is driven by a multiturn-primary, single-turn-secondary, current step-up toroidal transformer. The Precision High Energy-density Liner Implosion eXperiment (PHELIX) pulsed-power driver, which is currently under development at Los Alamos National Laboratory, Los Alamos, NM, can provide >;400 kJ of capacitively stored energy and peak load currents of >;5 MA to implode centimeter-size liners in 10-20 μs, attaining speeds of 1-4 km/s. Diagnosis of scaled-down liner implosion experiments will be performed with the 800-MeV proton radiographic (pRad) system at Los Alamos Neutron Science Center (LANSCE); therefore, PHELIX is designed to be portable with a footprint of only 8 ×25 ft <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The multiframe, high-resolution imaging capability of pRad will be used to study hydrodynamic and material phenomena. Experiments with scaled-down electromagnetic railguns, pulsed high-field magnets, and magnetic flux compression are also under consideration. This paper discusses the overall PHELIX design concept and layout, and details of the electromechanical design needed to ensure repeatable operation.

In situ optical microscopic observation of NiCoMnIn metamagnetic shape memory alloy under pulsed high magnetic field

In situ microscopic imaging observation was performed on Ni45Co5Mn36.7In13.3 metamagnetic shape memory alloy. Magnetic field-induced reverse martensitic transformation and heating-induced martensitic transformation were directly observed for the first time. The fraction of martensite phase was evaluated by contrast change from micrographs and critical magnetic fields were determined. Isothermal growth of martensite after magnetic field application was also observed. Comparison between the micrographs after the application of a magnetic field and on cooling also revealed the nature of the adiabatic process under a strong driving force.

Magnetic properties of Cr‐doped ZnO nanorods fabricated by hydrothermal method in a high pulsed magnetic field

AbstractCr‐doped ZnO diluted magnetic semiconductor (DMS) nanorods with nominal composition of 1 at.% were synthesized by a hydrothermal method with the assistance of a high pulsed magnetic field (HHPMF). All the Cr‐doped ZnO samples obtained with or without the applied high magnetic field exhibited room‐temperature ferromagnetic behavior. It is observed that the high magnetic field plays an important role in saturation magnetization of the samples. The effects of high magnetic field on the morphology, structure, and magnetic properties of the samples were discussed.

Neutron Laue Diffraction Study on the Magnetic Phase Diagram of MultiferroicMnWO4under Pulsed High Magnetic Fields

We have combined time-of-flight neutron Laue diffraction and pulsed high magnetic fields at the Spallation Neutron Source to study the phase diagram of the multiferroic material MnWO(4). The control of the field-pulse timing enabled an exploration of magnetic Bragg scattering through the time dependence of both the neutron wavelength and the pulsed magnetic field. This allowed us to observe several magnetic Bragg peaks in different field-induced phases of MnWO(4) with a single instrument configuration. These phases were not previously amenable to neutron diffraction studies due to the large fields involved.

Thermal expansion and magnetostriction of GdAg 2, and relations to the magnetoelastic paradox

The antiferromagnet GdAg 2 has been shown to be a good model system for the magnetoelastic paradox (MEP), because it exhibits large symmetry conserving magnetoelastic strains and the antiferromagnetic propagation vector breaks the tetragonal lattice symmetry (therefore a large symmetry breaking magnetoelastic strain can be expected in a single q magnetic structure). As in many similar Gd based compounds no symmetry breaking strain has been found in the experiment. In order to investigate this MEP further, we have measured magnetostriction and magnetization on a textured polycrystal. The behaviour closely resembles that of GdNi 2B 2C, the prototype system for the magnetoelastic paradox (MEP). Our forced magnetostriction data indicate that the crystal distorts in applied magnetic field and gives further evidence that the MEP is a low field effect. The observed phase transitions are in agreement with available specific heat and neutron diffraction data. Moreover, the saturation magnetic field was measured in high pulsed magnetic fields and agrees well with the value calculated from the Standard Model of Rare Earth Magnetism (SMREM).