A new class of Sm-TM magnets for operating temperatures up to 550°C

A breakthrough has been made for magnets to be used at high temperatures. A new class of Sm(Co_wFe_vCu_x Zr_y)_z type magnets with linear demagnetization curves up to 550°C has been developed. A new symbol, T_M, is introduced, which is defined as the maximum temperature at which the induction demagnetization curve of a magnet is a straight line. A magnet in this class can be made with its own unique T_M. There is a direct relationship between the optimum Co content and T_M. An equation has been established to relate the Co content and the T_M. Using the equation, magnets can be provided with the best combination of highest (BH)_max and a linear demagnetization curve for any application with a specified operating temperature. These magnets have high resistance to thermal demagnetization because of their low temperature coefficients of _i H_c which result in a higher _iH_c at high temperature. Thermal stability of these magnets at 300-550°C has been studied, showing that the loss due to metallurgical changes is <2% for new magnets at 550°C for 360 hr. Experiment confirms that coated magnets can be expected to have considerable life expectancy and relatively low magnetic losses at the intended T_M. Experiment also shows that, at high temperatures, the magnetic pinning strength in the magnets increases as the T_M increases. TEM microstructures for some magnets have been studied. Magnets with higher T_M have smaller cell sizes and larger volume of cell boundaries than conventional 2:17 magnets. It is believed that the large volume of cell boundaries plays a role in the high resistance to thermal demagnetization