Magnetic pinning strength for the new Sm-TM magnetic materials for use up to 550 degrees C

A new series of Sm(CowFevCuxZry)(z) alloys has been developed to produce ma gnets with high intrinsic coercivity H-i(c) at high temperatures for use up to 550 degrees C. The maximum use temperature is defined as T-M, which is the maximum temperature at which the extrinsic demagnetization curve is a s traight line. An important feature of the alloys with high T-M is a lower t emperature coefficient of H-i(c), beta. These magnets have a higher resista nce to demagnetization from increasing thermal agitation which occurs with increasing temperature. A study on magnetic pinning field H-p, which will b e explained in the text, vs T-M was conducted by measuring the initial magn etization curves of the magnets at 25 and 300 degrees C. The study shows th at as T-M increases, H-p increase at high temperatures. At 25 degrees C, al l magnets with T-M from 250 to 550 degrees C have H-p higher than 24 kOe, w hich is too high to be determined using a hysteresigraph. At 300 degrees C, the magnet with T-M=250 degrees C has H-p=7.0 kOe, and the magnet with T-M =550 degrees C has H-p=15.1 kOe. Higher pinning field at high temperatures (greater than or equal to 300 degrees C) provides a greater resistance to t hermal demagnetization, which leads to better performance at high temperatu res. (C) 2000 American Institute of Physics. [S0021-8979(00)24308-9].