Improved perpendicular anisotropy and permanent magnet properties in Co-doped Nd-Fe-B films multilayered with Ta

Multilayers of 200-nm thick Co-free or Co-doped Nd-Fe-B with 10-nm thick Ta were prepared by sputtering on heated glass substrates and investigated into the microstructure, texture and hard magnet properties. The perpendicularly textured Nd₂Fe₁₄B grains evolved in the multilayers with sizes neatly controlled by the thickness of the unit layer. Co was found to dissolve in the Nd₂Fe₁₄B grains, resulting in the enhanced c-axis texture possibly due to the modulated surface energy of the Nd₂Fe₁₄B phase. It was also found that Co boosts the crystallization and grain growth of the Nd₂Fe₁₄B phase, rapidly leading to the relatively stable multilayered structure where the dimension of the Nd₂Fe₁₄B grains is exactly defined by the thickness of the unit layer. Such effect of Co suppresses the local variation of the microstructure and minimizes the deterioration of the permanent magnet properties of the multilayer with an increased thickness of 10-μm.