obtain magnetically aligned, fully dense bulk materials.^79,80 With such efforts, the energy product has now been raised to the 40- to 45-MGOe level, shown in Figure 44 for the evolution of permanent-magnet alloys;⁸¹ there is no reason to believe that a limit has yet been reached. Other rare-earth/transitionmetal/metalloid intermetallic compounds now become attractive candidates for investigations along these lines. Additional research is also needed to attain higher Curie temperatures and better magnetic properties at elevated temperatures. But already the indications are that the high energy densities characteristic of these advanced magnetic intermetallic phases will spur new electronic-device designs toward greater efficiency and miniaturization— e.g., for electric motors, generators, actuators, and electroacoustical pick-ups.⁸¹ Strong permanent magnets have even been proposed in place of electromagnets for use in accelerators and in electron storage rings for synchrotron radiation.⁸² All these possibilities constitute another exciting prospect for front-line metallurgical research, development, and application.

Still another research and development sector for magnetic alloys lies in the magneto-optical recording of information.⁸³ Vacuum-deposited amorphous films of rare-earth/transition-metal alloys, such as GdCo, TbFe, GdTbFe,

FIGURE 44 Evolution of permanent-magnet alloys during the 20th century, according to the energy product (BH)_max as a figure of merit. From National Materials Advisory Board publication NMAB-426.⁸¹