Dresden High Magnetic Field Laboratory Research Articles

On the high-field characterization of magnetocaloric materials using pulsed magnetic fields

Magnetic refrigeration is a highly active field of research. The recent studies in materials and methods for hydrogen liquefaction and innovative techniques based on multicaloric materials have significantly expanded the scope of the field. For this reason, the proper characterization of materials is now more crucial than ever. This makes it necessary to determine the magnetocaloric and other physical properties under various stimuli such as magnetic fields and mechanical loads. In this work, we present an overview of the characterization techniques established at the Dresden High Magnetic Field Laboratory in recent years, which specializes in using pulsed magnetic fields. The short duration of magnetic-field pulses, lasting only some ten milliseconds, simplifies the process of ensuring adiabatic conditions for the determination of temperature changes, . The possibility to measure in the temperature range from 10 to 400 K allows us to study magnetocaloric materials for both room-temperature applications and gas liquefaction. With magnetic-field strengths of up to 50 T, almost every first-order material can be transformed completely. The high field-change rates allow us to observe dynamic effects of phase transitions driven by nucleation and growth as well. We discuss the experimental challenges and advantages of the investigation method using pulsed magnetic fields. We summarize examples for some of the most important material classes including Gd, Laves phases, La–Fe–Si, Mn–Fe–P–Si, Heusler alloys and Fe–Rh. Further, we present the recent developments in simultaneous measurements of temperature change, strain, and magnetization, and introduce a technique to characterize multicaloric materials under applied magnetic field and uniaxial load. We conclude by demonstrating how the use of pulsed fields opens the door to new magnetic-refrigeration principles based on multicalorics and the ‘exploiting-hysteresis’ approach.

Mode Conversion and Period Doubling in a Liquid Rubidium Alfvén-Wave Experiment with Coinciding Sound and Alfvén Speeds

We report Alfvén-wave experiments with liquid rubidium at the Dresden High Magnetic Field Laboratory. Reaching up to 63T, the pulsed magnetic field exceeds the critical value of 54T at which the Alfvén speed coincides with the sound speed. At this threshold, we observe a period doubling of an applied 8kHz cw excitation, which is consistent with the theoretical expectation of a parametric resonance between magnetosonic waves and Alfvén waves. Similar mode conversions are discussed as a possible mechanism for heating the solar corona.

Field-stepped broadband NMR in pulsed magnets and application to SrCu2(BO3)2 at 54 T

Pulsed magnets generate the highest magnetic fields as brief transients during which the observation of NMR is difficult, however, this is the only route to unique insight into material properties up to the regime of 100T. Here, it is shown how rather broad NMR spectra can be assembled in a pulsed magnet during a single field pulse by using the inherent time dependence of the field for the recording of field-stepped free induction decays that cover a broad frequency range. The technique is then applied to 11B NMR of the spin-dimer system SrCu2(BO3)2, a magnetic insulator known to undergo a series of field-driven changes of the magnetic ground state. At peak fields of about 54T at the Dresden High Magnetic Field Laboratory, 11B NMR spectra spanning a total of about 9MHz width are reconstructed. The results are in good accordance with a change from a high-temperature paramagnetic state to a low-temperature commensurate superstructure of field-induced spin-dimer triplets.

NMR shift and relaxation measurements in pulsed high-field magnets up to 58 T

Nuclear magnetic resonance (NMR) experiments at fields up to 58T in pulsed magnets at the Dresden High Magnetic Field Laboratory are reported. The challenge to resolve NMR shifts in these time-dependent fields is addressed for the first time, and it is shown that this can indeed be accomplished with high precision with an internal reference. As a result, signal averaging is possible during a single magnetic field pulse, but also for multiple pulses. Thus, even very weak signals can in principle be recorded and their shifts can be determined. In a second set of experiments, the measurement of nuclear relaxation is investigated. Using adiabatic inversion with the inherent time dependence of the magnetic field and small-angle inspection, it is shown that relaxation measurements are possible, as well. The shift experiments were performed with 27Al NMR on a mixture of aluminum metal and a Linde type A zeolite. For the relaxation studies, 27Al NMR and 69Ga NMR on the metals aluminum and gallium were preformed, respectively.

Observation of Anisotropic Exchange in a Spin Ladder by ESR

E. ƒiomara,∗, M. Ozerov, K.W. Kramer, Ch. Ruegg, S.A. Zvyagin Institute of Physics, Faculty of Sciences, P.J. ’afarik University, Park Angelinum 9, Ko2ice, Slovakia Dresden High Magnetic Field Laboratory (HLD), Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany Department of Chemistry and Biochemistry, University of Bern, Bern, Switzerland Laboratory for Neutron Scattering, Paul Scherrer Institut, Villigen PSI, Switzerland

CMR-B-Scalar Sensor Application for High Magnetic Field Measurement in Nondestructive Pulsed Magnets

In this paper, we present the investigation of the axial and radial magnetic-field distribution inside and outside of the bore of a nondestructive pulsed-field coil presently installed at the Dresden High Magnetic Field Laboratory (HLD). The array used for these magnetic-field measurements was made up of three CMR-B-scalar sensors based on nanostructured La-Sr-Mn-O films. The investigations were performed at a temperature of 270 K and at a peak field of 46 T. The experimental results fit well with calculations obtained using ANSYS code based on the finite element method (FEM). It is concluded that the CMR-B-scalar sensors can be successfully used for the investigation of the magnetic-field distribution in pulsed high magnetic field coils.

Magnet-Technology Development at the Dresden High Magnetic Field Laboratory

The Dresden High Magnetic Field Laboratory (HLD) is a user facility which provides scientists with the possibility to perform a broad range of experiments in pulsed magnetic fields. Recent progress in the magnet-technology development at the HLD has led to significant advances in achieving non-destructive pulsed magnetic fields close to the megagauss mark. Using 9.5 MJ dual-coil magnets with 16 mm bore, in 2011 a world-record field of 91.4 T has been achieved. Later 94.2 T have been reached. We report on the magnet design and performance of these magnets as well as on the design for the next generation of dual-coil magnets characterized by interchangeable inner sub-coils and improved control of the axial preload.

Status of the Pulsed-Magnet-Development Program at the Dresden High Magnetic Field Laboratory

The Dresden High Magnetic Field Laboratory (HLD) is a pulsed-field user facility which offers to researches a variety of experimental techniques combined with non-destructive pulsed magnetic fields. Recently a new, 9.5 MJ dual-coil magnet has been commissioned. This magnet has achieved magnetic field of 91.4 T in a 16 mm bore and it is available for users now. In this paper, we report on some key upgrades in the magnet design which have led to breaking the 90 T limit at the HLD. Further possible design improvements are discussed. In addition, we share our operational experience obtained with the pulsed magnets.

NMR signal averaging in 62 T pulsed fields

Nuclear Magnetic Resonance (NMR) experiments in pulsed high magnetic fields up to 62 T at the Dresden High Magnetic Field Laboratory ( Hochfeld-Magnetlabor Dresden) are reported. The time dependence of the magnetic field is investigated by observing various free induction decays (FIDs) in the vicinity of the maximum of the field pulse. By analyzing each FID’s phase and its evolution with time the magnetic field’s time dependence can be determined with high precision. Assuming a quadratic or cubic dependence on time near the field maximum its confidence is found to be better than ±0.03 ppm at low fields and ±0.8 ppm near 62 T. In turn, the thus obtained time dependence of the field can be used to demodulate and phase-correct all FIDs so that they appear phase-locked to each other. As a consequence signal averaging is possible. The increase in signal-to-noise ratio is found to be close to that expected theoretically. This shows that the intrinsic time dependence of the pulsed fields can be removed so that the NMR signals appear to be taken at rather stable static field. This opens up the possibility of performing precise shift measurements and signal averaging also of unknown, weak signals if a reference signal is measured during the same field pulse with a double-resonance probe.

Design and Performance of Non-Destructive Pulsed Magnets at the Dresden High Magnetic Field Laboratory

In this paper we consider various issues of design, fabrication, and performance of non-destructive pulsed magnets at the Dresden High Magnetic Field Laboratory. Currently, a variety of pulsed magnets are in operation in the laboratory. A 70 T/8.5 MJ magnet, having a 24 mm bore and generating field pulses of about 150 ms duration serves as a workhorse for external users and for in-house research. Smaller 60-65 T/1.5 MJ magnets with a bore of 20 mm and pulse duration of ~25 ms have been proven to be very reliable in operation. In addition, a new 90 T/9 MJ dual-coil magnet has recently achieved 87.2 T in a 20 mm bore. A 60 T/43 MJ longpulse magnet is currently tested. Questions of magnet longevity, coil monitoring, as well as magnetic-field measurements are addressed. Further magnet-technology developments and the route to 100 T are discussed.

Design of Non-destructive Pulsed Magnets at the HLD

In this paper, we consider several aspects of the design and construction of non-destructive pulsed magnets on the basis of work which is under way at the Dresden High Magnetic Field Laboratory (HLD). A number of pulsed magnets including 60 T/1.5 MJ and 70 T/8.5 MJ mono-coils have been successfully tested and are ready for operation. Some perspectives of the pulsed-magnet development are discussed. A way to achieve 100 T in non-destructive pulsed magnets and the role of various factors and challenges are addressed. Results of the finite element analysis (FEA) of the designed coils are presented.

Dresden pulsed magnetic field facility

We report on the status quo of the Dresden High Magnetic Field Laboratory (HLD) that is being set up at the Forschungszentrum Dresden-Rossendorf in Dresden, Germany. First pulsed-field coils reaching up to 71 T with a pulse duration of about 100 ms have been designed, constructed, and tested. A two-coil 100 T magnet and a long-pulse (1000 ms) 60 T magnet are under construction. Electrical-transport and magnetization experiments are running routinely in the pilot laboratory at the IFW Dresden. The feasibility of NMR experiments in pulsed-field environments has been proven.

Status quo of the Dresden High Magnetic Field Laboratory

We report on the recent progress made at the Dresden High Magnetic Field Laboratory (Hochfeld-Magnetlabor Dresden = HLD). This facility, under construction at the research center (Forschungszentrum) Rossendorf, is planned to open as user facility in 2007 offering access to various pulsed-field magnets. Besides the ultimate goal of constructing a multi-pulse magnet reaching 100T in a bore of 20mm with a peak-pulse duration of about 10 ms, further self-designed high-energy coils will be provided. For thermodynamic experiments, e.g., a pulsed coil for 60T in 40mm and 1 s is planned. The necessary energy of up to 50MJ for coil operation recently became available through a world-unique capacitor bank working at 24 kV. First user-type magnets for fields up to 71T for 100ms in a bore of 24mm have been tested successfully. As an outstanding feature of the laboratory, the bright light of a next-door free-electron-laser facility will allow dedicated high-field infrared spectroscopy. A broad range of experimental techniques is being developed both for user and in-house research in static and pulsed magnetic fields.

Pulsed-magnet design at the Dresden High Magnetic Field Laboratory

The current status of the pulsed-magnet program of the Dresden High Magnetic Field Laboratory (HLD) is reported. The non-destructive pulsed magnets for the HLD include a wide spectrum of coils designed for energies between 1 and 46MJ, magnetic fields of 60 - 100T, and pulse durations of 10 - 1000 ms. Various experimental techniques at pulsed magnetic fields will be available for external users soon. Some user magnets for first scientific experiments have been installed and tested. A 8.5MJ/70 T mono-coil magnet has been built and first test results for this magnet are presented. The design of a two-coil 46 MJ magnet for magnetic fields above 85T has been completed. This magnet is under construction now. Important issues of the coil design are numerical simulations of the pulsed-magnet performance. Both analytical approaches and finite-element analysis are used for these simulations at the HLD.

Coil Design for Non-Destructive Pulsed-Field Magnets Targeting 100 T

Progress and recent achievements in coil design are presented for the new Dresden High Magnetic Field Laboratory (HLD), which is under construction at the Forschungszentrum Rossendorf. This laboratory is planned to be open for external users in 2007. The facility is placed near a free electron laser which will offer the opportunity to perform infrared spectroscopy in pulsed magnetic fields. Implementation of various experimental techniques, such as transport, magnetization, specific heat, ultrasound, and magnetic resonance in pulsed magnetic fields up to 100 T are planned. Typical pulse durations will be in the range between 10 and 1000 ms with magnet bores ranging from 20 to 40 mm. The pulsed magnets will be energized by a 50 MJ/24 kV modular capacitive pulsed-power supply. With our newly designed coils, so far we were able to reach 65 T in a non-destructive manner. These coils are built using regular copper wire reinforced with an organic fiber (Zylon). Pulse durations for the various coils are between 20 and 50 ms. Different magnet failure modes have been analysed and possible improvements of the magnets are discussed. We also present numerical simulations of our pulsed magnets

The Dresden high-magnetic field laboratory – overview and first results

It is planned to build a 50 MJ pulsed field laboratory at the Forschungszentrum Rossendorf (near Dresden) to obtain magnetic fields up to 100 T with 10 ms pulse duration. This facility would provide the appealing possibility to have access to Zeeman energies in the energy range of the infrared free electron lasers (5–250 μm) that is now under construction at the radiation source ELBE in Rossendorf. For gaining experience in the construction and operation of pulsed magnets, a smaller pulsed field laboratory was established at the Institute for Solid State Physics and Materials Research Dresden (IFW Dresden) in 1999. The laboratory includes pulse magnets with peak fields up to 50 T in a 24 mm bore and a pulse length of about 11 ms, and a 40 T long pulse magnet with a 24 mm bore and a pulse length of about 130 ms. The coils are energized by a 1 MJ, 10 kV capacitor bank with thyristor switches. The bank is subdivided into four identical and independent units. A particular advantage is the possibility to reverse the polarity of the magnetic field pulse by means of a novel circuit with industrial circuit breakers. The design of the power supply is explained in detail. High-precision measurements of magnetization and magnetotransport in the temperature range of 1.5–300 K have been performed.