Some Introduction of Samarium Cobalt Magnet

Temperature compensated Samarium Cobalt magnet is referring to the Samarium Cobalt magnet with extremely low temperature coefficient of remanence.

Besides Terbium and Dysprosium, RCo5 compounds composed by other rare earth elements can maintain uniaxial easy magnetization characteristics under room temperature and above room temperature. In the meanwhile, μ0Ha at room temperature of these compounds are all larger than 10T due to the strong uniaxial anisotropy of Cobalt’s sublattice. It should be noted that NdCo5 has spin reorientation transition at 280K, then easy axis deviates from c-axis and μ0Ha at room temperature is merely 0.5T. Therefore, rare earth except Neodymium, Terbium, and Dysprosium can substitute part of Samarium to constitute (Sm, R) Co5 alloy with excellent uniaxial anisotropy in principle. Even SmCo5 already have relatively low temperature coefficient of remanence, it still unable to satisfy the requirements of travelling wave tube, gravity sensor, and gyroscope in aerospace or precision instrument. In order to reduce αBr to 0.02%/degree Celsius or even close to zero, magnet manufacturers must utilize ferrimagnetic coupling characteristics which caused by antiparallel arrangement of heavy rare earth’s (HR) and Cobalt’s atomic magnetic moment, then decline of Ms (T) in SmCo5 will be compensated by HRCo5. Ms (T) of GdCo5 and ErCo5 increased with the increasing temperature in the range of -150~450 and -270~250 degrees Celsius, respectively. Therefore, substitute Samarium by moderate Gadolinium or Erbium will be able to prepare (Sm, R) Co5 magnet with extremely low temperature coefficient of remanence. Temperature compensated 2:17 type Sm2(Co, Cu, Fe, Zr)17 magnets can also be prepared by the introduction of middle and heavy rare earth elements.

Aerospace and military required magnets that operated at temperatures higher than 400 degrees Celsius. In response to this requirement, magnet manufacturers was developing a new class of ultra-high temperature Samarium Cobalt magnet for use at temperatures up to 550 degrees Celsius.

High temperature stability of permanent magnets has two implications, including low temperature coefficient of remanence and low irreversible flux loss of open circuit. For low αBr magnet, the varies of magnetic flux was little with the increase of temperature. For the latter, magnetic flux under room temperature and high temperature might vary widely, but both must change little with time. The Maximum Working Temperature Tw is belonging to the second implication, then have the strong connection as to whether magnets have high intrinsic coercivity and low temperature coefficient of intrinsic coercivity or not. The combination of these two parameters will ensure magnet to maintain high enough intrinsic coercivity under high temperature and avoid knee point appears in B-H curve. Reduce absolute value of αHcj can improve Tw effectively compared with the enhancement of intrinsic coercivity when the composition is basically determined.