Magnetic Properties and Magnetic Domain Observation of Nd–Fe–B Sintered Magnets Treated by Grain Boundary Diffusion Process with Dy–Al Co-Sorption

Abstract

Effective grain boundary diffusion (GBD) process with Dy–Al co-sorption is applied to enhance the coercivity of Nd–Fe–B sintered magnets. The coercivity of the magnet (H_cJ = 1789 kA·m⁻¹) subjected to the present GBD treatment was observed to be superior to that of the untreated magnet (H_cJ = 1003 kA·m⁻¹) and the conventional GBD magnet (H_cJ = 1661 kA·m⁻¹) treated with DyAl alloy. In the present GBD magnet, the Dy–Al co-sorption process facilitated Dy diffusion into the center region of the magnet (thickness: 3.5 mm), resulting in high coercivity. Further, magnetic domain observations were made using magnetic force microscopy (MFM) to observe the thermal demagnetization behavior of the present GBD magnet. The present GBD magnet suppressed the continuous domain reversal of adjacent grains; thus, the partially persistent single-domain structure remained, even at 453 K.