Permanent magnet systems have some generic properties that, under some circumstances, make them not only mildly preferable over electromagnets, but make it possible to do things that can not be done with any other technology. After a general discussion of these generic advantages, some specific permanent magnet systems will be described. Special emphasis will be placed on systems that have now, or are likely to have in the future, a significant impact on how some materials research is conducted.

Many devices that employ magnetic fields are encumbered by massive solenoids with their equally bulky power supplies or by inefficient permanent-magnet structures designed for use with obsolescent magnet materials. This paper describes how the high-energy product materials are employed in several structures to afford mass and bulk reductions of an order of magnitude or more. Also discussed are novel designs that are not attainable with the older materials such as the alnicos. Substitution of solenoids with permanent magnets also eliminates considerable energy consumption and the attendant problems arising from generation of heat. In many cases, all this is accomplished within leakage-free systems. Among the designs described are: nuclear magnetic resonance imagers; cylindrical solenoidal field structures for klystrons and nonperiodic field TWT's; cylindrical field structures with arbitrary axial gradients for advanced gyrating beam sources; annular field sources for high harmonic gyrotrons; helical transverse field sources for circularly polarized radiation sources; miniature periodic permanent-magnet configurations; and clad permanent-magnet circuits for biasing fields in millimeter-wave filters. Where alternate designs exist, they are compared with regard to performance, bulk, and economy. All of the structures are in various stages of design and construction, and, for completed structures, comparisons are made between theoretical projections and actual performance.

The high remanence and coercivity of the new permanent magnet materials are of special interest in the static applications. High ordering temperature and large uniaxial anisotropy at the origin of their good permanent magnet properties are obtained in rare earth-transition metal compounds. Binary SmCo5 and Sm2Co17 and ternary Nd2Fe14B compounds are the basis materials of the best permanent magnets. New concepts of calculations of static devices with these magnets can be applied : the magnetization can be considered as rigid, the density of the surface Amperian current is constant, the relative permeability is approximately 1 and the induction calculations are linear. Examples of hexapoles with Sm-Co and NdFeB magnets are described and the performances are compared. The problems of temperature behaviour and corrosion resistance are underlined.

Nd-Fe-B and Sm-Co permanent magnets have been irradiated with fission neutrons and gamma rays. Irradiated samples were periodically removed for room temperature measurements of the open-circuit remanence. Hysteresis loops were measured before and after irradiation. For neutron irradiation, two Nd-Fe-B magnets showed a rapid loss of remanence, while a third magnet from another manufacturer decayed more slowly, suggesting that the radiation hardness of Nd-Fe-B magnets may depend on microstructural details. Irradiation in the Omega West Reactor at Los Alamos with fast neutrons caused the fast-decay samples to have an Wtial loss of remanence of 1% for irradiation at 350 K to a fluence of 1015 n/cm2. Both SmCo5 and Sm2Co17 magnets showed excellent resistance to radiatifg-induied loss of remanence for neutron irradiation to a fluence of 2.6×1018 n/cm2. Results for gamma radiation showed no loss of remanence for a dose of about 49 Mrad using a 60Co source. Possible mechanisms for radiation-induced loss of magnetic properties are discussed.

Magnetic Resonance Imaging technology has advanced on many fronts. Two important areas are the improvement of signal-to-noise levels and the understanding of imaging pulse sequence optimization. Based on these advances, low cost imagers using very low field permanent magnets are providing images of diagnostic quality.