磁石・半導体 不可逆減磁率の改善された低Ｎｄ系希土類ボンド磁石

Abstract

Isotropic bonded magnets made of rapidly quenched Nd-Fe-B powder (MQP-B powder) are widely used in various applications because of their superior magnetic properties and shape flexibility. However, it is not so easy to obtain fully magnetized magnets when a multipole magnetizing is necessary. Bonded magnets made of row rare-earth Nd-Fe-B powder (MQP-Q powder) show superior magnetizability to that of those made of MQP-B powder, because of the lower value of Hci . Therefore, the magnets seem to be suitable for applications where full magnetization is difficult. However, the irreversible flux losses of the bonded magnets made of MQP-Q powder are higher than that of bonded magnets made of MQP-B powder. Therefore, it is necessary to improve the irreversible flux loss in order to adapt these magnets to various applications. The effects of Nb addition on magnetic properties and irreversible flux loss were studied on bonded magnets with composition of Nd8Fe86-xB6Nbx , where x= 0 - 3. An irreversible flux loss was measured at Pc = 2 after exposure at 393 K for 3.6 ks in air. It was found that the Nb addition of 2 at.% or more decreased the irreversible flux loss. The value was less than 5 %, similar to that obtained with MQP-B magnets. B r decreased with the increase in Nb content. The effect of Nd content on the magnetic properties and irreversible flux loss was also studied on the bonded magnets with compositions of NdxFe92-xB6Nb2 , where x = 6 - 8. The bonded magnet with the optimum composition of Nd6.5Fe85.5B6Nb2 had Br similar to that of MQP-Q magnets that did not contain Nb, and the value of irreversible flux loss was comparable to that of MQP-B magnets. A multipole magnetizability test on the bonded magnets with the above optimum composition was