Magnetic properties and microstructure of ultra-high operating temperature hot deformed Nd-Dy-Fe-Co-B magnets

The magnetic properties and microstructure of melt-spun ribbons and hot-deformed Nd-Dy-Fe-Co-B magnets with ultra-high operating temperature were systematically investigated. Coercivity increased with Dy content, from 906 kA/m in Dy-free magnets to 2197 kA/m in the Dy-10% magnets. The temperature coefficient of remanence ( α ) improved from −0.123%/K to −0.063%/K, and the temperature coefficient of coercivity ( β ) enhanced from −0.62% to −0.44%/K over the temperature range of 300 K to 400 K. The operating temperatures at which the irreversible magnetic flux loss ( h irr ) reached −5% increased from 362 K for Dy-free magnets to 534 K for the Dy-10% magnets, significantly expanding the application range of these magnets under ultra-high operating temperatures. Microstructure observations revealed that the grain size and aspect ratio decreased after adding Dy, which lowered the magnets' effective demagnetization factor ( N eff ) and enhanced coercivity and thermal stability. The addition of Dy also resulted in the formation of large cluster grains inside the magnet, inhibiting the alignment of adjacent grains along the c-axis and having a negative impact on the remanence.