Analytical microscope studies of sintered Nd-Fe-B magnets

Various sintered Nd
15
Fe
77
B
8
permanent magnets supplied by different producers have been examined by analytical electron microscopy. An identical microstructure was found in all of the different magnets. Three phases were detected by means of high resolution electron microscopy, electron diffraction and x-ray microanalysis. Besides the hard magnetic boride phase Nd
2
Fe
14
B, a soft magnetic boride phase close to Nd
2
Fe
7
B
6
, and a Nd-rich sintering aid phase (d.h.c.p. structure) were identified. The Nd-rich phase preferentially occurs along grain boundaries as a thin layer with about 10 nm tickness. The soft magnetic phases determine the magnetization reversal and limit the coercivity of sintered Nd-Fe-B magnets.