The Influence of Co and Nb Additions on the Magnetic Properties and Thermal Stability of Ultra-high Intrinsic Coercivity Nd-Fe-B Magnets

The effect of Co and Nb additions on the magnetic properties and thermal stability of ultra-high intrinsic coercivity Nd-Fe-B magnets has been investigated. The results show that the remanence (B r ) and maximum energy product (BH)max of sintered Nd-Fe-B magnets first increases, and reaches a maximum, then starts to decrease with increasing Co content. The intrinsic coercivity and temperature coefficients of remanence (α) decrease, and the temperature coefficients of coercivity (β) increase with increasing Co content. The minimum reversible magnetic flux loss, temperature coefficients of reversible magnetic flux, total magnetic flux loss and irreversible magnetic flux loss are obtained when the Co content is 7.5 at.%. The temperature coefficients of coercivity (β) and remanence (α) for sintered Nd9Dy6Fe79−x Nb x B6 magnets from 300 K to 513 K are 0.36 %/K and 0.127 %/K respectively when the content of Nb is 1.0 at.%. The reasons for the variation on magnetic properties and temperature coefficients were analyzed.