Striking effect of Hf addition on magnetic properties and thermal stability of Nd13Fe81−xB6Hfx (x = 0-1.0) alloys

In order to improve the thermal stability of Nd2Fe14B-type rare earth permanent magnets, Nd13Fe81−xB6Hfx (x = 0-1.0) alloys are fabricated by a melt spinning technique. The magnetic properties, microstructure and thermal stability of Nd13Fe81−xB6Hfx (x = 0-1.0) alloys are investigated. When x = 0.5, a coercivity of 505 kA/m is obtained at 450 K, which is much higher than that of 290 kA/m for the sample without Hf. Curie temperature (Tc) decreases slightly from 588 K to 579 K. The temperature coefficients of remanence (α) and coercivity (β) of the ribbons are improved from −0.20 %/K, −0.48 %/K for x = 0 to −0.17 %/K, −0.34 %/K for x = 0.5 in the temperature range of 300-450 K, respectively. The betterment of the magnetic properties and thermal stability with Hf doping is discussed in terms of the grain refinement and a more uniform microstructure. Furthermore, it is found out that the domain wall pinning mechanism is responsible for enhancing the coercivity of Nd13Fe81−xB6Hfx alloys.