Pulsed High Magnetic Fields Research Articles

A concise 40 T pulse magnet for condensed matter experiments

There is a growing interest in using pulsed high magnetic field as a controlling parameter of physical phenomena in various scientific disciplines, such as condensed matter physics, particle physics, plasma physics, chemistry, and biological studies. We devised a concise and portable pulsed magnetic field generator that produces a 40 T field with a pulse duration of 2 ms. It is assembled using only off-the-shelf components and a homemade coil that leverages small computers, Raspberry Pi, and Python codes. It allows for straightforward modification for general purposes. As working examples, we show representative applications in condensed matter experiments of magnetoresistance, magnetization, and magnetostriction measurements for graphite, NdNi2P2, and NdCo2P2, respectively, with the maximum magnetic field of 41 T and the lowest temperature of 4.2 K.

Why the pyrochlore-like antiferromagnet NaCu3F7 is magnetically non-frustrated

We present a theoretical study of the magnetic properties for the pyrochlore-like NaCu3F7 compound, which surprisingly experience little or no frustration. The magnetic effective exchange interactions were calculated using ab-initio methods explicitly treating the electronic correlation. A model Hamiltonian (quantum Heisenberg Hamiltonian, and for comparison a spin 1/2 Ising Hamiltonian) was built from these interactions and used to determine the zero temperature magnetic order versus magnetic field. The magnetic order at zero magnetic field is non frustrated and associated with the propagation vector q→=(0,0,0) . The magnetization versus magnetic field reveals the existence of a 1/3 plateau that could be observed in high-pulsed magnetic field experiments. Analyzing the magnetic interactions, we highlight the importance of the magnetic ion nature, and the lattice distortion, in the non-frustrated nature of the NaCu3F7 magnetic structure, despite its triangular/Kagome subnetworks. We believe that this non-frustrated behavior could also take place in other triangular copper-based systems.

Origin of the metamagnetic transitions in Y0.9Tb0.1Fe2D4.3

Deuterium insertion was used to tune the magnetic properties of Y0.9Tb0.1Fe2 Laves phase towards an itinerant electron metamagnetic (IEM) behavior. The latter is highly sensitive to chemical changes and external parameters. The structural and magnetic properties of Y0.9Tb0.1Fe2D4.3 were investigated using various neutron powder diffraction experiments in addition to magnetic measurements under steady and pulsed high magnetic fields up to 60 T. The deuteride crystallizes in a monoclinic structure (Pc space group) with 4.3 D atoms located in 18 tetrahedral interstitial sites. At zero field, it undergoes a ferrimagnetic-antiferromagnetic (FiM-AFM) transition at TM0 = 90 K, accompanied by an anisotropic magnetostriction and a negative cell volume expansion of 0.6 %. A second AFM-PM transition is observed at 146 K. Under pulsed magnetic field at 4.2 K, the deuteride displays a multistep magnetic behavior from ferrimagnetic to a ferromagnetic state, which can be attributed to a stepwise rotation of the Tb moments. The ZFC-FC magnetization curves at low fields exhibit an irreversibility below 90 K, followed by a sharp decrease in magnetization at the FM-AFM transition. Between 90 K and 130 K, the magnetization curves display an IEM behavior, with the transition field increasing linearly with temperature.

Laser-plasma accelerated proton beam transport system using high-field pulsed solenoid magnet

An energetic proton beam with a high divergence cone angle of ∼10°, generated by the interaction of a 25 fs, 800 nm Ti: Sapphire laser pulse with a thin metal foil target, was transported and focused at a specified distance from the source. A pulsed high-voltage solenoid, which generates a magnetic field of 5.7 T at a current of 8 kA, was developed in-house for this purpose. The profile of the proton beam was monitored online at various positions using a combination of a fast thin plastic scintillator and a CCD camera. The effect of solenoid misalignment on the focused proton beam was also investigated experimentally. In addition, the proton beam was transported out of the vacuum chamber into the ambient air for radiography application. A proton flux of ∼2 × 108 protons (energy >4 MeV) was transported and focused at a distance of 1.27 m from the target with a transmission efficiency of 30 % in a single shot. Detailed simulations incorporating particle tracing and transfer matrix method were performed to highlight the role of beam chromaticity and the impact of spherical harmonics on the focusing characteristics of the solenoid. The simulation results qualitatively reproduce the experimental observations. The solenoid provides energy-selective proton focusing for a broad energy proton beam. The proton beam was used for the radiography of reference meshes and has the potential to be used for radiobiological irradiation studies.

Mechanical Behaviors of Polymer-Based Composite Reinforcements within High-Field Pulsed Magnets.

The development of pulsed magnets capable of generating magnetic fields exceeding 100 Tesla has been recognized as a crucial pursuit for advancing the scientific research on high magnetic fields. However, the operation of magnets at ultra-high magnetic fields often leads to accidental failures at their ends, necessitating a comprehensive exploration of the underlying mechanisms. To this end, this study investigates, for the first time, the mechanical behaviors of Zylon fiber-reinforced polymers (ZFRPs) within pulsed magnets from a composite perspective. The study begins with mechanical testing of ZFRPs, followed by the development of its constitutive model, which incorporates the plasticity and progressive damage. Subsequently, in-depth analyses are performed on a 95-T double-coil prototype that experienced a failure. The outcomes reveal a notable reduction of approximately 45% in both the radial and axial stiffness of ZFRPs, and the primary reason for the failure is traced to the damage incurred by the end ZFRPs of the inner magnet. The projected failure field closely aligns with the experiment. Additionally, two other magnet systems, achieving 90.6 T and 94.88 T, are analyzed. Finally, the discussion delves into the impact of transverse mechanical strength of the reinforcement and axial Lorentz forces on the structural performance of magnets.

Unconventional room-temperature negative magnetoresistance effect in Au/n-Ge:Sb/Au devices

Non-magnetic semiconductor materials and their devices have attracted wide attention since they are usually prone to exhibit large positive magnetoresistance (MR) effect in a low static magnetic field environment at room temperature. However, how to obtain a large room-temperature negative MR effect in them remains to be studied. In this paper, by designing an Au/n-Ge:Sb/Au device with metal electrodes located on identical side, we observe an obvious room-temperature negative MR effect in a specific 50 T pulsed high magnetic field direction environment, but not in a static low magnetic field environment. Through the analysis of the experimental measurement of the Hall effect results and bipolar transport theory, we propose that this unconventional negative MR effect is mainly related to the charge accumulation on the surface of the device under the modulation of the stronger Lorentz force provided by the pulsed high magnetic field. This theoretical analytical model is further confirmed by regulating the geometry size of the device. Our work sheds light on the development of novel magnetic sensing, magnetic logic and other devices based on non-magnetic semiconductors operating in pulsed high magnetic field environment.

Fe doping induced cluster/spin glass state and metamagnetic transition in phase separated La0.5Sr0.5Mn1−xFexO3

We report the impurity doping effects in manganites La0.5Sr0.5Mn1−xFexO3 (0 ≤ x ≤ 0.2) and the field-induced metamagnetic transition in which the antiferromagnetic insulating phase transforms into ferromagnetic metallic phase. The Rietveld refined results of XRD data display no obvious structure change with a significant degree of Fe3+ doping on Mn sites. Significant ferromagnetism suppression and magnetic inhomogeneity tendency upon Fe3+-doping are evidenced, phase separated and spin-glass like states are identified. With applying a pulsed high magnetic field up to 50 T, a metamagnetic transition was induced, especially clear for x ≥ 0.1 compounds, which exhibited an irreversible phase transition from antiferromagnetic to ferromagnetic phase, and a saturation magnetization was obtained. The replacement of Mn3+ by Fe3+ ions eliminates the effects of lattice structure change on the magnetic and electronic properties because of the very similar ionic size of Mn3+ and Fe3+, but reduces the Mn3+/Mn4+ ratio and depopulates the number of available hopping sites and the hopping electrons, thus weakens the double exchange interaction. The occurrence of the AFM superexchange interaction via Fe3+–O2−–Fe3+ and Fe3+–O2−–Mn3+ bonds may bring about the competition between the antiferromagnetic ordering and the ferromagnetic ordering, leading to a cluster/spin-glass behavior in the samples with high Fe dopants concentration.

Non-stoichiometric TbFe2Mnx compounds: Magnetic anisotropy, magnetostriction and thermal expansion

In magnetostrictive RFe2 (R – rare earth) materials, magnetic properties such as magnetocrystalline anisotropy and Curie temperature can have a profound impact on the magnetostriction, often reducing its value in practically applicable magnetic field at normal conditions. Tuning the atomic structure by Mn alloying is one of the research strategies that allows to improve both elastic and magnetoelastic properties. Here we investigate novel non-stoichiometric TbFe2Mnx (0 ≤ x ≤ 0.25) compounds in which Mn partially replaces both Tb and Fe. Curie temperature and magnetic moment values decrease with manganese alloying. We interpret these effects as a consequence of lowered Fe-Fe exchange interactions which is confirmed within two-sublattice molecular field model. Magnetocrystalline anisotropy estimated by law of approach to magnetic saturation in high pulsed magnetic fields shows trend of decrease with Mn doping. Notably, this cause significant increase of linear magnetostriction (up to 25%) for TbFe2Mnx compounds at liquid nitrogen temperature. Thermal expansion declined due to growth of magnetic contribution in magnetically ordered state, which is linked to volume magnetostriction. These changes make TbFe2Mnx promising material for practical application. Thus, it was shown that manganese alloying opens new way for tuning magnetocrystalline anisotropy and magnetostriction in non-stoichiometric Laves phase compounds.

Piston-cylinder cell made of Ni–Cr–Al alloy for magnetic susceptibility measurements under high pressures in pulsed high magnetic fields

We developed a metallic pressure cell made of 56Ni–40Cr–4Al (Ni–Cr–Al) alloy for use with a non-destructive pulse magnet and a magnetic susceptibility measurement apparatus with a proximity detector oscillator (PDO) in pulsed magnetic fields of up to 51 T under pressures of up to 2.1 GPa. Both the sample and sensor coil of the PDO were placed in the cell so that the magnetic signal from Ni–Cr–Al would not overlay the intrinsic magnetic susceptibility of the sample. A systematic investigation of the Joule heating originating from metallic parts of the pressure cell revealed that the increase in sample temperature is negligible at 1.4 K in magnetic fields of up to 40 T in the field-ascending process for the maximum applied magnetic field of 51 T. The effectiveness of our apparatus was demonstrated by investigating the pressure dependence of the magnetization process of the triangular-lattice antiferromagnet Ba3CoSb2O9.

Strong magnetoelastic coupling in MnCoSi compounds studied in pulsed magnetic fields

The orthorhombic MnCoSi compounds have been found to present a large magnetoelastic coupling, which is regarded as the source for the magnetocaloric effect (MCE) and the magnetostrictive effect. As a result, these compounds are potential materials for caloric applications such as solid-state refrigeration. In the present study, we offer fundamental insights in the magnetoelastic coupling in these compounds based on their structural, metamagnetic, and MCE behavior. The directly measured adiabatic temperature change ($\mathrm{\ensuremath{\Delta}}{T}_{\mathrm{ad}}$) in different initial temperatures (down to 18 K) and pulsed magnetic fields (up to 40 T) presents a moderate MCE performance (the maximum $\mathrm{\ensuremath{\Delta}}{T}_{\mathrm{ad}}=--3.1\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ for a field change of 13 T), which results from the metamagnetic behavior of these compounds. Furthermore, the magnetization measurements in pulsed (and static) magnetic fields indicate that the magnetoelastic coupling is significantly enhanced for increasing fields resulting in an improved saturation magnetization. The metamagnetic transition is continuously pushed to lower temperatures in higher fields. The phase diagram constructed from the experimental transition temperatures ${T}_{t}$ and the critical magnetic fields ${\ensuremath{\mu}}_{0}{H}_{\mathrm{cr}}$ indicate that the transition is terminated below 18 K and that ferromagnetism is stabilized for fields above 22.3 T. Our results provide unique insights into the strong magnetoelastic coupling under high pulsed magnetic fields, providing guidelines for the design of giant magnetocaloric materials for future caloric applications.

High field magnetism of the triangular lattice antiferromagnet CsFeCl$_3$ under high pressure

Magnetization measurements of the triangular lattice antiferromagnet CsFeCl_{3}3 at 1.4 K for H \parallel cH∥c were performed in pulsed high magnetic fields of up to 51 T under high pressures of up to 0.80 GPa. At ambient pressure, the magnetization below H_{c1}Hc1 = 4 T is small, and then it changes steeply between H_{c1}Hc1 and H_{c2}Hc2 = 12 T, followed by a gradual increase in magnetization up to H_{m}Hm = 33 T where a two-step metamagnetic transition occurs. With increasing pressure, the H_{c1}Hc1 and H_{m}Hm shifted to the low-field side, while the H_{c2}Hc2 shifted to the opposite side. The change in H_{m}Hm may depend on the difference in the single-ion anisotropies on pressure in the lowest JJ = 1 and the excited J=2J=2 states.

Effect of high intensity pulsed magnetic field (30 T) on microstructure and tribological properties of Ni-based coatings

Pulsed magnetic fields can improve ferromagnetic and paramagnetic materials by improving their stress structure, domain variation, phase structure distribution and grain size of both solid and molten metals. Therefore, we strengthened the Ni-based wear-resistant coating by using the high-intensity (30 T) pulsed magnetic field equipment independently developed by our research group. The results show that the magnetic domains appeared as sheet domains and showed sinusoidal distribution after pulsed magnetic field intensification. The crystal structure is improved, the residual compressive stress is increased and the tribological coefficient is decreased. This study provides a new perspective on the design of high-strength metal base coatings for various applications.

Realisation of the reconfigurable pulsed high magnetic field facility and its scientific application at Wuhan National Pulsed High Magnetic Field Centre

AbstractTo generate arbitrary shape magnetic field waveforms for advanced scientific research, a reconfigurable pulsed high magnetic field facility (PHMFF) was developed at Wuhan National Pulsed High Magnetic Field Centre (WHMFC). First, the basic elements of PHMFF are introduced, and a ternary physical model composed of energy storage unit, magnet, transmission circuits and other auxiliary units is summarised to describe various magnetic field systems. Second, in order to realise the reconfiguration of magnetic field systems based on detailed elements, the control system with the ability of dynamic construction and control sequence reconfiguration is designed. On this basis, the PHMFF has been realised and various magnetic field systems are constructed to produce arbitrary shape magnetic field waveforms, such as half‐sine, ultra‐high, flat‐top and repetitive field pulses, which not only enhances the capability and efficiency of PHMFF, but also makes more scientific research possible in pulsed magnetic fields. So far, a peak magnetic field of 94.8 T, a flat‐top magnetic field of 64 T/10 ms and a repetitive magnetic field waveform of 20 T/60 Hz have been achieved, and some experiments and studies on the physical properties of materials have been carried out at WHMFC.

High-field magnetization and electronic spin resonance study in the twisted honeycomb lattice α-Mn2V2O7

We report the single-crystal growth of Mn2V2O7 and the results of magnetic susceptibility, high-field magnetization up to 55 T and high-frequency electric spin resonance (ESR) measurements for its low-temperature α phase. Two antiferromagnetic (AFM) ordering at 17.5 K and 3 K and obvious magnetic anisotropy are observed in α-Mn2V2O7 upon cooling. In pulsed high magnetic fields, the compound reaches the saturation magnetic moment of ∼10.5 μ B for each molecular formula at around 45 T after two undergoing AFM phase transitions at H c1 ≈ 16 T, H c2 ≈ 34.5 T for H//[] and H sf1 = 2.5 T, H sf2 = 7 T for H//[]. In these two directions, two and seven resonance modes are detected by ESR spectroscopy, respectively. The ω 1 and ω 2 modes of H//[] can be well described by two-sublattice AFM resonance mode with two zero-field gaps at 94.51 GHz and 169.28 GHz, indicating a hard-axis feature. The seven modes for H//[] are partially separated by the critical fields of H sf1 and H sf2, displaying the two signs of spin-flop transition. The fittings of ω c1 and ω c2 modes yield zero-field gaps at 69.50 GHz and 84.73 GHz for H//[], confirming the axis-type anisotropy. The saturated moment and gyromagnetic ratio indicate the Mn2+ ion in α-Mn2V2O7 is in a high spin state with orbital moment completely quenched. A quasi-one-dimensional magnetism with a zig-zag-chain spin configuration is suggested in α-Mn2V2O7, due to the special neighbor interactions caused by a distorted network structure with honeycomb layer.

CHIMERA Fusion Technology Facility: Testing and Virtual Qualification

The Combined Heating and Magnetic Research Apparatus (CHIMERA) fusion technology test facility is under construction. The facility will be uniquely capable of semi-integral testing of fusion materials and component modules up to the size of the ITER test blanket module box, under combined conditions of in-vacuum high heat flux, static and pulsed magnetic fields, and high-temperature/high-pressure water cooling. This paper reports the high-level capabilities of the CHIMERA baselined design and the planned program of testing and describes the proposed strategy for use of simulations for virtual testing, qualification, and in-situ monitoring. The first step in testing of a component mock-up is to take data from as-built geometry and other measurements and transmit them to an integrated computational model that can closely mimic the physical asset and form a digital replica. Not only can this digital replica be queried in advance of physical testing in the facility, allowing optimization of the test program, but combined with subsequent test data, it also can deliver much greater insight into experimental results than can be obtained using test data alone. The digital replica is used as the basis for a digital twin, which is live coupled to the running experiment, and is under development as a proposed key facet of fusion reactor surveillance in-service. Physical mock-ups for testing can be subjected to in-vacuum heat flux up to 0.5 MW/m2 over the entire surface while within a strong horizontal magnetic field. The central field can be up to 4 T with a peak in the test region of 5 T. The same component mock-ups can also be subjected to repeated magnetic field pulses with ramp rate 12 T/s, which can simulate loading conditions of a plasma disruption. Facility upgrades are underway to include a liquid metal circulation loop to allow the study of magnetohydrodynamics effects and to add a high-heat-flux system using a very high-power continuous-wave laser to achieve divertor-relevant heat fluxes of 20 MW/m2 over the area of a small-scale mock-up. Four examples are given to illustrate the physical testing program that is currently foreseen.

Measurement System for Short-Pulsed Magnetic Fields.

A measurement system based on the colossal magnetoresistance CMR-B-scalar sensor was developed for the measurement of short-duration high-amplitude magnetic fields. The system consists of a magnetic field sensor made from thin nanostructured manganite film with minimized memory effect, and a magnetic field recording module. The memory effect of the La1-xSrx(Mn1-yCoy)zO3 manganite films doped with different amounts of Co and Mn was investigated by measuring the magnetoresistance (MR) and resistance relaxation in pulsed magnetic fields up to 20 T in the temperature range of 80-365 K. It was found that for low-temperature applications, films doped with Co (LSMCO) are preferable due to the minimized magnetic memory effect at these temperatures, compared with LSMO films without Co. For applications at temperatures higher than room temperature, nanostructured manganite LSMO films with increased Mn content above the stoichiometric level have to be used. These films do not exhibit magnetic memory effects and have higher MR values. To avoid parasitic signal due to electromotive forces appearing in the transmission line of the sensor during measurement of short-pulsed magnetic fields, a bipolar-pulsed voltage supply for the sensor was used. For signal recording, a measurement module consisting of a pulsed voltage generator with a frequency up to 12.5 MHz, a 16-bit ADC with a sampling rate of 25 MHz, and a microprocessor was proposed. The circuit of the measurement module was shielded against low- and high-frequency electromagnetic noise, and the recorded signal was transmitted to a personal computer using a fiber optic link. The system was tested using magnetic field generators, generating magnetic fields with pulse durations ranging from 3 to 20 μs. The developed magnetic field measurement system can be used for the measurement of high-pulsed magnetic fields with pulse durations in the order of microseconds in different fields of science and industry.

Quantum transport phenomena in magnetic topological insulators

In the past decade, magnetic topological insulators have been an important focus in condensed matter physics research. The intricate interplay between the nontrivial band topology and spin, orbit, charge, and dimensionality degrees of freedom can give rise to abundant exotic topological quantum states and topological phase transitions. Measuring the transport properties of magnetic topological insulators is a crucial approach to exploring their exotic properties, which is of significant scientific importance in deepening our understanding of topological quantum states. Simultaneously, it also holds substantial potential applications in the development of novel low-power electronic devices. In this work, experimental progress of transport researches of magnetic topological insulators is reviewed, including quantum anomalous Hall effect and topological quantum phase transitions in magnetically doped topological insulators, the quantum anomalous Hall phase, axion insulator phase and Chern insulator phase in intrinsic antiferromagnetic topological insulator MnBi<sub>2</sub>Te<sub>4</sub>, as well as the helical phase emerged from the Chern insulator in pulsed high magnetic fields. Finally, this work analyzes the future direction of development in magnetic topological insulators, and the transport phenomena that have not been understood in these systems, offering an insight into and perspectives on the potential breakthroughs to be achieved in this area of research.

Nuclear Magnetic Resonance Measurements in High Flat-Top Pulsed Magnetic Field Up to 40 T at WHMFC

Nuclear magnetic resonance (NMR) technique benefits from the high magnetic field not only due to the field-enhanced measurement sensitivity and resolution, but also because it is a powerful tool to investigate field-induced physics in modern material science. In this study, we successfully performed NMR measurements in the high flat-top pulsed magnetic field (FTPMF) up to 40 T. A two-stage corrected FTPMF with fluctuation of less than 10 mT and duration of longer than 9 ms was established. Besides, a Giga-Hz NMR spectrometer and a sample probe suitable for the pulsed-field condition were developed. Both free-induction-decay and spin-echo sequences were exploited for the measurements. The derived <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">93</sup> Nb NMR results show that the stability and homogeneity of the FTPMF reach an order of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ppm / 10 ms and 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ppm / 10 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> respectively, which is approaching a degree of maturity for some researches on condensed matter physics.

Comprehensive analyses of buckling and stress failure of high-field pulsed magnets under biaxial Lorentz force body load

This paper will discuss the failure mechanism of high field pulsed magnets based on a failed pulsed magnet of 85 T. Firstly, the stress failure possibility is analyzed by an ANSYS-ACP finite element model. The results show that the stress failure risk is low. Then a comprehensive model including both stress failure and structural buckling is proposed and discussed. It is found that the structural buckling and stress failure would co-exist and interact with each other. The model predicts the pulsed magnet suffered from stress failure after structural buckling and finally collapsed at 79 T. The consistency of the theoretical results with that in experiments show the validity of the comprehensive model.

Possible stripe phases in the multiple magnetization plateaus in TbB4 from single-crystal neutron diffraction under pulsed high magnetic fields

We present a single-crystal neutron diffraction study on the Shastry-Sutherland lattice system TbB$_4$ at zero magnetic field and under pulsed high magnetic fields up to 35 T applied along the crystallographic $c$ axis. While our results confirm the magnetic structures at zero-field as well as those at the half- and full-magnetization plateaus, they offer new insight into the $\frac{2}{9}$- and $\frac{1}{3}$-magnetization plateaus observed in this system. A stripe model of polarized 4-spin-plaquettes whose stripe density proportionally increases with the macroscopic magnetization is in full agreement with the neutron diffraction data. Equally well suited alternative models exist which explain the observed Bragg peaks which are inherently limited in a pulsed high magnetic field experiment. We discuss the different intensity distribution in $Q$ space which can be used to distinguish these models in future experiments.