Temperature Compensated Magnets

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. μ₀H_a 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 μ₀H_a 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 M_s (T) in SmCo₅ will be compensated by HRCo₅. M_s (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.