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 Pr
17
Fe
76.5
B
5
Cu
1.5
. 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 Pr
17
Fe
76.5
B
5
Cu
1.5
magnets are: B
r
= 12.5 kG, iH
c
= 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.