The recent rapid growth in the emerging areas of magnetic and magnet-related materials research and applications has led to worldwide recognition of the increased importance of research and technology using high magnetic fields. New high-field magnet facilities and major upgrades of existing facilities are being planned and implemented by a number of countries, among them Japan, Germany, France, the Netherlands, Belgium, Great Britain, Poland, Australia, and the United States. Over the next ten years, these developments will advance the state of the art in magnet-related materials science and technologies by a significant quantum jump. Support by many of the national agencies and a strong corporate commitment to stimulate rapid growth in the development of capabilities at higher magnetic fields and in related technologies results in part from an awareness of the impact these technologies will have in developing the new emerging industrial technologies of the 21st century.

The Francis Bitter National Magnet Laboratory (FBNML) at the Massachusetts Institute of Technology has been one of the pre-eminent facilities in developing and advancing science and technology in high magnetic fields. The new U.S. National High Magnetic Field Laboratory (NHMFL) at Florida State University, at the University of Florida, and at Los Alamos National Laboratory builds on the success of existing facilities. NHMFL will provide the necessary environment to develop the next generation of high magnetic fields: 30–50-tesla continuous fields, 60-tesla quasi-continuous fields, and pulsed fields from 60–1,000 tesla. The ability to develop broad user capabilities at these extreme fields is crucial for the advancement of the frontiers of science and of magnet-related industries.

The study of materials which have electronic phase transitions is a very active area. Such phase transitions include charge and spin density formation, as well the superconducting condensation in a rapidly expanding variety of materials. It is now common to lump these phenomena under the heading of correlated electron physics, involving as they do the essential role of electron-electron interactions in their occurrence. There are also materials in which there is found no electronic phase transition, but whose properties indicate strong electron-electron effects, such as a number of the so-called heavy fermion compounds. The part of condensed matter theory which addresses the particular physics of such materials is generally known as many-body physics. How to effectively treat strong electronic interactions theoretically is very much an unsolved problem, and theory does not give much more than limited guidance to the experimental research in this area. External magnetic fields have proved to be effective experimental probes of the properties of such systems, and the advent of increasingly strong pulsed fields is opening new possibilities for exposing and pulling apart the underlying electronic ground state of many such materials.

In single-crystal organic salts, we find a keen competition between superconducting, magnetic, insulating, and metallic states. The physics of these materials is further enriched by the sensitivity of these states to pressure, temperature, chemical formulation, and magnetic field. A growing international community of scientists have turned their attention to these materials, and are applying the techniques and theories of metal and semiconductor physics to probe these new systems. In this article we will explore these materials. We will discover that these materials have given us many new things: a renaissance in fermiology, new high-magnetic-field states of matter, a bulk quantum Hall effect, new challenges in the calculation of energy bands on a small energy scale, and elusive behavior which seems one step away from our present understanding of physics in low dimensions. Electron correlations probably play an important role in determining the phenomena, and should be considered in more microscopic theoretical treatments of these systems.

The spin-polarized phases of the quantum fluids and solids, liquid 3He, solid 3He, and spin-aligned hydrogen have generated considerable excitement over the past fifteen years. The introduction of high magnetic fields (B ∼ 10–30 T) in conjunction with low temperatures (T ≲ 100 mK) has given rise to opportunities for exploring some of the new phases predicted for these materials. There is a broad range of physical phenomena that can be accessed in this regime of parameter space—unconventional superfluidity, unusual magnetic ordering, Bose-Einstein condensation and Kosterlitz-Thouless transitions, to name a few. This is most surprising since this plethora of complicated states of matter are present in some of the most uncomplicated materials. The rich variety of phases found in these materials are all examples of collective phenomena of quantum many-body systems, and they serve as prototypes for developing an understanding of magnetism and order/disorder processes in other systems, and for the design and characterization of new materials.

In this article, we examine materials behavior in the magnetic field region from about 40 T to 500 T using pulsed magnet technology. Examples of materials science using two different pulsed magnet technologies are described in this article.

Semicontinuous Magnets

Since the late 1960s, the University of Amsterdam has operated a semicontinuous magnetic field installation that produces magnetic fields up to 40 T with typical time constants of about one second. The magnet coil is constructed from hard-drawn copper wire with a reinforcement cylinder of maraging steel positioned at roughly one third of the outer diameter. Before operation, the coil is cooled to 30 K by cold neon gas. The power for this installation is taken directly from a 10 kV connection to the public electricity grid. By means of a thyristor-based power control system, highly flexible field-time profiles can be realized: step-wise pulses can be generated with field levels constant within 10−4 during 100 ms; linearly increasing and decreasing fields as well as exponentially ripple-free decreasing fields are other examples of standard field-time profiles. Among the measuring techniques frequently used are magnetization, magneto-transport, quantum oscillations, relaxation phenomena, etc. Temperatures at which experiments can be performed range from 400 mK to room temperature. In the Netherlands, the Amsterdam High Field Facility has recently been combined with the High Magnetic Field Laboratory in Nijmegen, where static magnetic fields up to 30 T are produced in hybrid magnet systems, to form the Amsterdam-Nijmegen Magnet Laboratory (ANML). The high field research of ANML comprises semiconductors, magnetism in transition-metal compounds, heavy-fermion physics, superconductors, organic conductors, and magnetic separation. We present here a few selected topics.

A useful superconducting conductor must have several properties. Some of the key properties among these are illustrated by the cross section of a Nb-47wt%Ti/Cu composite (Figure 1) which was manufactured for the dipole magnets of the Superconducting Super Collider (SSC). It represents the state of the art for conventional conductor fabrication and is thus an excellent place to start in considering what is needed for any new conductor. First among the essential properties is a high critical current density (Jc); the lower limit of useful Jc is ~104 A/cm2, but really useful values lie between 105 and 106 A/cm2. The SSC conductor achieves this at fields up to 9 T at 4.2 K, the normal temperature used for magnets cooled by liquid helium.

A critical second requirement is that the superconductor be paralleled by an intimately connected good normal conductor, in this case high-conductivity Cu. One function of the Cu is to stabilize the superconductor against small temperature disturbances that lead to flux jumps that could result in local quenching of superconductivity. This requirement forces the subdivision of a given cross section of the superconductor into many filaments having a maximum diameter of no more than about 50 μm, since bigger filaments store more electromagnetic energy than can safely be deposited in the filament without locally heating it above its critical temperature (Tc). One advantage of high-temperature superconducting (HTS) materials is that they can operate at temperatures above ~10 K. Since the specific heat is a strongly increasing function at low temperatures, this permits the safe filament size to greatly increase too. The need to minimize hysteresis losses, however, often provides a separate drive to minimize the filament diameter, as in the conductor of Figure 1, where there are some 7,000 filaments which are only 6 μm in diameter. The overall Cu:Nb-Ti ratio is about 1.5:1. This represents a compromise between the need to minimize the dilution of the supercurrent density by Cu and the need to provide sufficient high-conductivity normal metal to pass the current when the magnet makes the transition from the superconducting to the normal state (a quench).

The development of high-field magnets for pulsed-field applications is the subject of considerable research activity throughout the world. Induced field strengths in excess of 30 T can be produced only as pulses generated by the discharge of energy, e.g., from a capacitor bank into a resistive solenoid. A variety of electromagnetic design issues relate to the pulse duration, field strength, and volume of the coil; however, from the viewpoint of materials selection and coil design, there are two salient property requirements: (1) high electrical conductivity to minimize the temperature rise due to the flow of current in the coil, and (2) high mechanical strength to resist the Lorentz forces exerted during the pulse. Such forces can result in catastrophic failure, as illustrated in Figure 1, because the coil is, in essence, stressed in the manner of an internally pressured cylindrical vessel. At lower stresses, plastic distortion of the coil is observed.