Temperature compensated magnets are referring in particular to the Samarium Cobalt magnets 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. μ0Ha at room temperature of these compounds are all larger than 10T due to the strong uniaxial anisotropy of Cobalt’s sublattice. NdCo5 has spin reorientation transition at 280K. Then its easy axis will deviate 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 superior uniaxial anisotropy in principle. Even SmCo5 already have relatively low temperature coefficient of remanence, it still unable to fulfil the requirements of travelling wave tube, gravity sensor, and gyroscope in aerospace or precision instrument. In order to reduce low temperature coefficient of remanence to 0.02%/degree Celsius or even close to zero, magnet manufacturers must utilize ferrimagnetic coupling characteristics which generated by antiparallel arrangement of heavy rare earth’s (HR) and Cobalt’s atomic magnetic moment, thus 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. 2:17 type Sm2(Co, Cu, Fe, Zr)17 temperature compensated magnets can also be prepared by the introduction of middle and heavy rare earth elements.
