Abstract
Nd2Fe14B-type permanent magnets have been widely applied in various fields such as wind power, voice coil motors, and medical instruments. The large temperature dependence of coercivity, however, limits their further applications. We have systematically investigated the magnetic properties, thermal stabilities and coercivity mechanisms of the (Pr0.2Nd0.8)13Fe81-xB6Hfx (x=0, 0.5) nanocrystalline magnets fabricated by a spark plasma sintering (SPS) technique. The results indicate that the influence of Hf addition is significant on magnetic properties and thermal stabilities of the (PrNd)2Fe14B-type sintered magnets. It is shown that the sample with x = 0.5 at 300 K has much higher coercivity and remanent magnetization than those counterparts without Hf. The temperature coefficients of remanence (α) and coercivity (β) of the (Pr0.2Nd0.8)13Fe81-xB6Hfx magnets are improved significantly from -0.23 %/K, -0.57 %/K for the sample at x = 0 to -0.17 %/K, -0.49 %/K for the sample at x = 0.5 in the temperature range of 300-400 K. Furthermore, it is found out that the domain wall pinning mechanism is more likely responsible for enhancing the coercivity of the (Pr0.2Nd0.8)13Fe81-xB6Hfx magnets.
Highlights
Nd2Fe14B-type permanent magnets have been widely applied in various fields such as wind generators, voice coil motors (VCM) and medical instruments since they were invented in 1984.1,2 Nd-Fe-B magnets, have a low Curie temperature and their temperature dependence of coercivity is large
This paper summarizes the results of our systematic investigation of Hf influence on the high temperature magnetic properties, thermal stabilities and coercivity mechanisms of the Pr-Nd-Fe-B-based sintered magnets
The grinded ribbons were placed in a cylindrical graphite die with a diameter of 20 mm in vacuum followed by spark plasma sintering
Summary
Nd2Fe14B-type permanent magnets have been widely applied in various fields such as wind generators, voice coil motors (VCM) and medical instruments since they were invented in 1984.1,2 Nd-Fe-B magnets, have a low Curie temperature and their temperature dependence of coercivity is large. The thermal stability of the magnets is decreased drastically with increasing temperature so that ordinary Nd-Fe-B magnets cannot operate at elevated temperatures.[3,4,5] The low Curie temperature of the magnets and large temperature dependence of coercivity severely limit their further applications, especially in high-tech and new resources energy areas such as aerospace and hybrid electric vehicle (HEV). Rare earth elements are extracted from associated ore. The relative abundance of the Nd:Pr ratio in rare-earth ore is in the range of 3-4:1.13 To investigate the effect of Hf addition on the sintered magnets, the (Pr0.2Nd0.8)13Fe81-xB6Hfx magnets were prepared. This paper summarizes the results of our systematic investigation of Hf influence on the high temperature magnetic properties, thermal stabilities and coercivity mechanisms of the Pr-Nd-Fe-B-based sintered magnets
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