Nd₂Fe₁₇ nanograins effect on the coercivity of HDDR NdFeB magnets with low boron content

Relationships between the coercivity of hydrogenation disproportionation desorption recombination (HDDR) Nd_12.5Fe_81.5-xCo₆B_x bonded magnets and boron content were investigated. Nd₂Fe₁₇ phase with planar magnetic anisotropy is present in the microstructure when x=4at%-5.88at%, which does not reduce the coercivity of the bonded magnets. High-resolution transmission electron microscopy (TEM) images show that Nd₂Fe₁₇ phase exists in the form of nanocrystals in the Nd₂Fe₁₄B matrix. There is an exchange-coupling interaction between the two phases so that the coercivity of HDDR Nd_12.5Fe_81.5-xCo₆B_x bonded magnets is hardly reduced with a decrease in boron content.