Phase structure and magnetic properties of La/Ce substituted nanocomposite SmCo5/α-Fe magnets prepared by high energy ball milling and subsequent annealing

The phase structures and magnetic properties of isotropic nanocomposite permanent magnetic materials with the nominal composition of (Sm_1-xR_x)Co₅ (x = 0, 0.25, 0.5, 0.75, 1; R = La, Ce) + 25 wt% α-Fe prepared by high-energy ball milling and subsequent annealing have been investigated systematically. It is found that the phase structure of La-doped nanocomposite magnets is quite different from that of the Ce- doped. The hard phase of Ce-doped nanocomposite magnet is 2:7 phase and unchangeable with increasing the Ce content and annealing temperatures (≤650 °C), while that of La-doped nanocomposite magnets undergoes a phase transition from 2:7 phase to 1:7 and 2:17 hard phases with increasing the La content and annealing temperatures. Both magnetic performance of La and Ce doped nanocomposite magnets shows a tendency to decrease as La or Ce content increases. The analysis of hysteresis loop reveals that both La and Ce doped nanocomposite magnets exhibit the strong ferromagnetic exchange coupling between hard and soft magnetic phases. Surprisingly, the magnetic performance of La-doped SmCo₅/a-Fe is much superior to that of the Ce-doped although the Ce-doped Sm-Co hard phase has a relatively higher intrinsic magnetic property. The mechanism behind is found to be related to the change of Fe soft phase after adding La. Our results demonstrate that the substitution of Sm by La instead of Ce can produce the high-performance and low-cost SmCo₅/a-Fe nanocomposite magnets. Our study is of significance to balance the utilization of the rare-earth resource.