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(w)Fe(v)Cu(w)Zr(y))(x) type magnets with linear demagnetization curves up to 550 degreesC 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, 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 (i)H(c) at high temperature. Thermal stability of these magnets at 300-550 degreesC has been studied, showing that the loss due to metallurgical changes is <2% for new magnets at 550<degrees>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.