Improving the hard magnetic properties by intragrain pinning for Ta doped nanocrystalline Ce-Fe-B alloys

To develop Ce based permanent magnets with high performance/cost ratio, Ta doping is was employed to enhance the magnetic performance of Ce-Fe-B alloys. For melt spun Ce₁₇Fe_78-xTa_xB₆ (x = 0–1) alloys, the coercivity H_c increases from 439 to 553 kA/m with increasing x value from 0 to 0.75. Microstructure characterizations indicate that Ta doping is helpful for grain refinement. A second phase of TaB₂ is observed in Ce₁₇Fe_77.25Ta_0.75B₆ alloy, which acts as the pinning center of the magnetic domains, resulting in the change of coercivity mechanism from nucleation type to nucleation + pinning type. The micromagnetic simulation confirms that non-magnetic particles within hard magnetic phase can increase the demagnetization field around them and it is crucial for preventing the further magnetization reverse by pinning effect. Take the advantage of Ta doping for enhancing the coercivity, Ce content of Ce-Fe-B alloy can be further cut down to increase the remanence J_r due to the reduced volume fraction of CeFe₂ phase and increased Fe/Ce ratio. As a result, a good combination of magnetic properties with H_c = 514 kA/m, J_r = 0.49 T, and the maximum energy product (BH)_max = 36 kJ/m³ have been obtained in Ce₁₅Fe_79.25Ta_0.75B₆ alloy. It is expected that the present work can serve as a useful reference for designing new permanent magnetic materials with low-cost.