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Magnetic and Structural Characterization of Nd-Fe-B Sintered Permanent Magnets

机译：Nd-Fe-B烧结永磁体的磁性和结构表征

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Magnetic, structural, and chemical characterization using a hysterisigraph, transmission electron microscope, scanning electron microscope, and x-ray diffractometer were carried out on sintered Nd-Fe-B permanent magnets of nominal composition Nd sub 14 Fe sub 78 B sub 8 . Applying a maximum field of 23 kOe, the following magnetic properties were measured: B/sub r/ = 11.37 kG, H/sub c/ = 9.62 kOe, /sub i/H/sub c/ = 12.19 kOe, and (BH)/sub max/ = 28.83 MGOe. BH loop studies suggested that these magnets were ''nucleation-controlled'' magnets, which reversed their magnetization by the nucleation and growth of reverse magnetic domains. This conclusion was supported by microstructural studies, which revealed the presence of domain walls within the grains. The general microstructure was found to consist of defect free grains about 5 mu m in diameter of the hard magnetic matrix phase Nd sub 2 Fe sub 14 B, surrounded by a highly defective Nd-rich fcc grain boundary phase with lattice parameter approx. =5.6 A. This grain boundary phase also contained significant amounts of oxygen, some dissolved iron, and no boron. Small amounts of a third highly defective boride phase with lattice parameters a approx. = 7.6 A and delta c approx. = 30.5 A was also observed. A fourth phase, a bcc surface phase with lattice parameter a approx. = 2.9 A was determined to be an artifact of ion milling. The compatibility of this microstructure with a nucleation-controlled magnet is discussed, along with some processing suggestions for improving the magnetic properties through microstructural design. 20 refs., 34 figs., 4 tabs. (ERA citation 13:022014)

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