Magnetic micro-structural uniformity of die-upset Nd-Fe-B magnets

Magnetic micro-structural uniformity of die-upset Nd-Fe-B magnets" (2012). Si-Hwang Liou Publications. Paper 101. magnets have been prepared with height reduction (h) in the range of 60 to 88%. The energy product as high as 50.4 MGOe was obtained in the sample with h $ 70%. The magnetic domains of the samples are revealed by using magnetic force microscopy (MFM). The average domain widths of the die-upset samples with surface normal parallel (//) and perpendicular (\) to the loading direction are in the range of w // : 0.4-0.6 lm; w \ : 0.9-3.8 lm, respectively. These interaction domains are formed due to the strong inter-granular exchange interaction and magnetostatic interaction between grains. It was found that the ratio of / rms // to / rms \ is a good indicator for the quality of the magnet, where the / rms // and / rms \ are defined as the root-mean-square values of phase shift for the MFM images. The microstructures have been investigated by scanning electron microscopy (SEM), MFM and SEM results indicate the magnetic and crystalline microstructures are uniform for the sample with h $ 70%, giving rise to the highest magnetic performance among these samples.