Hot-pressed SmCo5/DyF3 composite magnets with high electrical resistivities

DyF3 powders have been milled in different processes and SmCo5 permanent magnets with DyF3 additions have been prepared by hot-pressing method. Influences of milling process, particle sizes, morphologies and amounts of DyF3 on the microstructures, electrical resistivities and magnetic properties of the hot-pressed SmCo5/DyF3 composite magnets have been investigated. The results show that DyF3 milled in ethanol has much smaller particle size and more concentrated size distribution than that milled in argon and obtained flake and rice shapes. The DyF3 powders milled in ethanol for 0.5 h obtained the smallest average size of 1.16 mu m. The DyF3 powders milled in argon agglomerated and their particle sizes increased. The SmCo5/DyF3 magnets with DyF3 milled in ethanol had higher electrical resistivities than those samples with the same amounts of DyF3 unmilled and milled in argon and obtained the highest resistivity of 120 mu S2 center dot cm when the milling time in ethanol was 2 h. With the increase of the milling times, the remanences of the SmCo5/DyF3 magnets with DyF3 milled in argon increased firstly and then decreased, and their coercivities decreased, thus their maximum magnetic energy products, (BH)max, had little changes. When the milling time was 0.5 h, the (BH)max of the SmCo5/DyF3 magnet with DyF3 milled in ethanol increased to 6.43 MGOe. With further increase of the milling times of DyF3 in ethanol, the (BH)max of the SmCo5/DyF3 magnets decreased. The electrical resistivities of the SmCo5/DyF3 magnets increased monotonously with the increase of the DyF3 amounts, but the excessive amounts of the DyF3 additions led to the deterioration of the magnetic properties of the SmCo5/DyF3 magnets. When the doping amount was 11 wt%, the SmCo5/DyF3 magnets obtained the highest resistivity of 186 mu S2 center dot cm, which is 129 % higher than that of the undoped SmCo5 magnet (81 mu S2 center dot cm). Whilst its remanences and (BH)max decreased from 5.78 kGs, 7.71 MGOe to 5.01 kGs, 3.84 MGOe, respectively.