Permanent magnets, samarium-cobalt

The S -band system uses a samarium cobalt permanent magnet, with a fixed field of 1180 G that is swept by a coil over a narrow range of 135 G. This corresponds to a frequency of 3.5 GHz. The system (Figure 3.81) includes an integrated touch screen, internal computer, thermoelectric cooler, and power supply. The instrument is available in an x-band version (9.5 GHz 3480 200 G). 

In the early 1970 s when samarium-cobalt magnets were first being proposed as a replacement for platinum-cobalt in microwave tubes, few could have anticipated the success that was to follow. Notwithstanding the traumas brought about by a quadrupling of cobalt prices, their use has grown steadily to the point where they now command a vitally important position in the permanent magnet market. 

The sealing of a rotating shaft under low leakage conditions is extremely difficult, therefore the stirrer shaft was built completely encapsulated by austenitic material and the transmission of the torque was realised using a permanent magnetic coupling. The magnets were based on samarium-cobalt and are able to transmit a torque of 135 Nm. 

New permanent magnet materials, such as samarium-cobalt and, a fortiori, neodymium-iron-boron alloys, are also of special interest in the design of static devices with specific magnetic-field configurations. Apart from high remanence and coercive force values of magnets made of these materials, Chavanne et al. (1987) emphasize the presence of large anisotropy fields in the conception of these devices. 

Alnico alloys in permanent magnets with e.g. 10% Al, 18% Ni, 12% Co, 6% Cu and 54% Fe. See further samarium-cobalt magnets in chapter 17 Rare Earth Metals ... 

Permanent magnets having properties several times superior to any other known materials were developed in 1967. Praseodymium, yttrium, samarium, lanthanum, and cerium are alloyed with cobalt in the range... 

Among the rare-earths, samarium is the most commonly used because it provides the best permanent-magnet property. Other rare-earth elements are sometimes employed in combination with samarium to meet special requirements. The compounds SmCos and Sm2Coi7 are the most important magnetic materials among the cobalt-lanthanide alloys. 

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