Rare earths in space communications

I have enjoyed reading several items on the rare-earth elements in Physics Today over past few years. David Kramer’s most recent piece focused topic (February 2021, page 20) was about neodymium-based magnets, but readers might be interested to learn of another class magnets based samarium. Among their applications are traveling wave tubes (TWTs), which form backbone world’s entire space communications system.The core feature TWTs is a stack samarium–cobalt (SmCo5 or Sm2Co17) magnetic rings, each magnetized opposition its neighbor. One design uses 25 cm 16 rings that 4 diameter. The can amplify and transmit millimeter waves frequency ranges 300 MHz 50 GHz. They bandwidths as high two octaves, power gains 40–70 dB, output powers watts megawatts. also exhibit excellent reliability. Voyager 1, launched 1977, has SmCo TWT produced by Watkins-Johnson still broadcasting from more than 23 billion kilometers away Earth!The large satellites geosynchronous orbit around 20–50 provide many essential services. Complete world coverage requires polar orbits. Fortunately, Iridium Communications now maintains constellation 66 low-Earth-orbit geosynchronous-orbit satellites, taken together, with access space-based because discovery development SmCo5 Sm2Co17 late 1960s.In 1966 Karl Strnat Gary Hoffer reported finding promising properties yttrium–cobalt compound YCo5. following year, they colleagues new family cobalt-based permanent magnet materials.11. K. et al., J. Appl. Phys. 38, 1001 (1967). https://doi.org/10.1063/1.1709459 researchers substituted other rare earths for Y determined optimal choice practical applications. Alden Ray continued line study ultimately discovered Sm2Co17, even impressive properties. That research possible only separation process developed Department Energy’s Ames Laboratory Manhattan Project made pure available first time.SmCo5 superior platinum–cobalt replaced terms properties, cost, size, weight. At present, remain choices applications, particularly those require very low operating temperatures. Uses include gyros launch vehicles, brushless high-torque motors dental medical tools, aircraft radar, computer disk drives.SmCo an extremely coercive force, measure ability resist demagnetization, energy product (the maximum B H fields during demagnetization), do work. products 20 megagauss oersteds (160 kJ/m3) 32 MGOe (250 kJ/m3), respectively. appropriate at temperatures absolute zero (−273 °C) °C 350 Sm2Co17.Importantly, field produce parallel c-axis hexagonal unit cell never flips easy basal plane any temperature. phenomenon, known magnetocrystalline anisotropy, gives application designers great flexibility shape.Neodymium-iron-boron 1984, far better ordinary Their 55 (440 useful temperature range between −138 150 °C. Therefore, NdFeB moderate-temperature such electric car MRI devices. already superconducting used older MRIs, mitigating claustrophobia size issues. however, neodymium-iron-boron TWTs. Thus, technologies will coexist peacefully areas not overlap.ReferenceSection:ChooseTop pageReference <<1. https://doi.org/10.1063/1.1709459, Google ScholarCrossref, ISI© 2021 American Institute Physics.