EVIDENCE OF DOMAIN-WALL PINNING IN W-DOPED (NDDY)(FECO)B SINTERED MAGNETS

Addition of tungsten (1-2 at. %) is very effective in improving coercivity of (Nd,Dy)-(Fe,Co)-B sintered magnets both at room temperature and elevated temperatures in addition to improving thermal stability. Transmission electron microscopy shows that there exists a WFeB precipitate phase inside the Nd 2Fe14B (2-14-1) matrix grain. The WFeB phase is plateletlike, and occasionally appears to have its largest dimension running parallel to the c axis of the 2-14-1 matrix phase. The orientation relationship between the WFeB precipitate and the matrix is found to be (102) WFeB∥(220)2-14-1, and [010]WFeB∥[002] 2-14-1. Domain walls jump from a position alongside the WFeB particles to a new position alongside others upon turning on magnetic field of the objective lens, as evidenced by Lorentz microscopy, denoting the ability of domain-wall pinning by the strain field around the WFeB precipitate. As a result, this provides extra hindrance to domain-wall motion and leads to enhanced coercivity and thermal stability, particularly at elevated temperatures.