Transformation of coercivity mechanism and evolution of microstructure in high performance Nd-Dy-Fe-Co-B thick films

• Published in: Journal of alloys and compounds 2022-11, Vol.923, p.166477, Article 166477
• Main Authors: Ye, Z.X., Zhao, X.T., Liu, W., Liu, L., Wu, J.X., Li, Y., Ma, J., Ju, H.Z., Song, Y.H., Zhang, Z.D.
• Format: Article
• Language: English
• Subjects: Buffer layers; Cobalt; Coercivity; Coercivity mechanism; Columnar structure; Crystal growth; Crystal structure; Crystals; Dysprosium; Evolution; Extrusion; Film thickness; Iron; Magnetic anisotropy; Magnetic films; Magnetization reversal; Microstructure; Nd elements accumulate; Nd-Dy-Fe-Co-B thick film; Neodymium; Nucleation; Permanent magnets; Pinning; Rare earth elements; Thick films
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2022.166477

It is important to understand the relationship between coercivity and microstructure for the development of high performance rare-earth permanent magnets. In this paper, the effects of film thickness on perpendicular magnetic anisotropy, coercivity mechanism, magnetization reversal process and microstructure of Nd-Dy-Fe-Co-B thick films are systematically investigated by varying film thickness from 1 to 12 µm. It is found that the coercivity mechanism transforms from a mixed type dominated by pinning to another mixed type dominated by nucleation. In addition, the evolution of grain shape from irregular spherical crystals to columnar ones occur at film thickness of 3 µm. The columnar crystals form on the capping layer and grow toward the buffer layer. When the film is thicker than 6 µm, Nd elements accumulate on the Ta buffer layer. With increasing the film thickness, the columnar crystal structure can grow throughout the whole thick film, and the Nd-rich phase is extruded onto the buffer layer, while the pinning effect weakens and the nucleation mechanism is dominated. This work can help us better understand the relationship between coercivity mechanism and microstructure of thick rare-earth permanent magnetic films. •The c-axis orientation of Nd-Dy-Fe-Co-B thick film tends to be disordered.•Coercivity mechanism transforms from pinning to nucleation dominated.•The evolution of grain shape from irregular spherical crystals to columnar ones.•Nd elements aggregate in the buffer layer due to the stress in the film.•Reveals the relationship between coercivity mechanism and microstructure.