Abstract
英 文 摘 要 Single- and multi-layer NdFeB films were prepared by sputtering with or without a buffer layer or a spacer layer. Multi-layer (NdFeBx/Nbz)n films showed enhanced coercivity significantly due to the reduced grain size. For a (NdFeB25nm/Nb)16 film, room temperature coercivity is up to 23 kOe being much larger than the coercivity of NdFeB single-layer film (9 kOe) with the same thickness of 400nm prepared under the same conditions. The average grain size changes from 24nm to 167nm. Some Nd2Fe14B grains are enriched by Nb and isolated as the thickness of spacer layer Nb increases, at annealing temperature 628oC. Perpendicular anisotropic Nd-Fe-B film can be obtained as deposited at high temperature. High deposition temperature enhances the growth of columnar grain structure. Texture of films can be changed with different underlayer such as W, Mo, Cr, or Pt. Isotropic Nd-Fe-B films can be obtained by depositing at room temperature followed by post annealing at high vacuum. Coercivity mechanism of Nd-Fe-B, (NdFeB/Nb)n films were discussed by modified micromagnetic models. That is to say the testimony of the microstructure parameters of the Nd-Fe-B, (NdFeB/Nb)n films. According to the fitted results, the range of aK, describing the inhomogeneities of anisotropy at grain surface and boundary varied from 0.37-0.70. The value of aK larger than 0.3 and exhibit the nucleation mechanism of NdFeB films under the assumption of temperature independent aK. Microstructure parameter was also related to the observed microstructure. Interdiffusion, distortion of grain boundary or second phase precipitation contribute to the value of microstructure parameters aK and Neff . Minor loops of NdFeB films exhibit the mixed type magnetization behavior. Neither exactly the pinning type nor nucleation type mechanism. Therefore the pheno- menological model was used to understand the formation of reversed domain. Domain pattern was investigated by MFM and found to be in the dimension about 50-100nm.