Magnetic Properties of Cast and Hot-Pressed Pr-Fe-B Magnets

A new process has been developed to produce high-energy-product bulk Pr-Fe-B magnets without the handling of any magnetic powder or powder-like ribbons. This process consists of three main steps, casting, hot-pressing and annealing, and it minimizes the oxygen contamination of magnets. A typical composition of a cast alloy is Pr17Fe76.5B5Cu1.5. Using this type of alloy, crystal alignment along the c-axis is easily induced by hot-pressing. Copper plays two important roles in this process: its addition simultaneously achieves high coercivity and excellent magnetic alignment. The magnetic properties of hot-pressed Pr17Fe76.5B5Cu1.5 magnets are: Br = 12.5 kG, iHc = 10.0 kOe, and (BH)max = 36.2 MGOe. The cast alloy of this composition also has an iHc of 7.3 kOe and a (BH)max of 9.2 MGOe after annealing at 1000°C for 24 hours. The step rise in the initial magentization curve indicates a nucleation-controlled coercivity mechanism.