A New Class of Permanent Magnetic Materials for High Temperature Applications

A new class of Sm2TM17 type permanent magnetic materials has been developed to meet the needs of applications at high temperatures. These magnets have high to moderate energy product (BH)max, high intrinsic coercivity iHc with low temperature coefficient of iHc, and straight-line demagnetization curves up to 550°C. A straight-line demagnetization curve provides greater design flexibility and facilitates reduced size and weight of magnetic circuits. A straight-line demagnetization curve is even more important for dynamic and highly loaded applications where high demagnetization forces are encountered. Examples of dynamic applications include generators, motors, jet engine start generators, and electro-magnet actuators. Highly loaded applications include the periodic arrangement of magnets in traveling wave tubes. A new symbol, TM, is introduced, which is defined as the maximum temperature at which the demagnetization curve is a straight line. An important feature of these magnets with high TM is a lower temperature coefficient of iHc, β, which gives these magnets a great resistance to thermal demagnetization and leads to better performance at high temperatures. This paper reports the magnetic properties vs. temperature for this new class of magnets, and compares them to the best conventional magnets, in order to illustrate the improvements that have been made.