Revealing high coercivity in Nd-Fe-B with gradient rare earth-rich phase sizes

Area of Science:

• Materials Science
• Physics
• Magnetism

Background:

• Conventional methods for enhancing permanent magnet coercivity often depend on expensive rare elements, limiting performance and recyclability.
• Microstructural engineering is key, but current approaches face cost and material limitations.

Purpose of the Study:

• To investigate a novel method for improving coercivity in sintered magnets by controlling rare-earth-rich phase (RERP) sizes.
• To achieve higher coercivity without compromising remanence in Nd-Fe-B magnets.

Main Methods:

• Fabrication of (Nd0.7Pr0.3)31Fe(ball)M1B0.95 (M = Cu, Co, Al, Ga, wt%) sintered magnets with controlled gradient RERP sizes.
• Application of top-down gradient stress (compressive to tensile) to induce RERP migration along grain boundaries.
• Utilizing micromagnetic simulations and magneto-optical Kerr effect measurements to analyze magnetization reversal behavior.

Main Results:

• A significant coercivity increase of up to 14.91 kOe (11.60% higher than control) was achieved without sacrificing remanence (14.21 kGs).
• Directional magnetization reversal was observed, driven by gradient RERP sizes and resulting in gradient demagnetizing fields.
• The study demonstrated that controlled RERP size gradients are crucial for enhanced magnetic properties.

Conclusions:

• The discovered directional magnetization reversal mechanism, linked to gradient RERP sizes, offers a pathway to high-performance permanent magnets.
• Regulating RERP size distribution is vital for optimizing coercivity in Nd-Fe-B magnets.
• This approach provides a cost-effective alternative to traditional methods, reducing reliance on precious elements.