Crystal Structure and Lattice Constant of Nd-rich Phase in Nd-Fe-B Films

摘要

The coercivity and Nd-rich phase are changed in Nd-Fe-B films by oxidation and subsequently annealing. The strain induced at the interface of Nd_2Fe_(14)B/Nd-rich is thought to influence on the interfacial microstructure and the coercivity. In this study, lattice constant of Nd-rich phase is evaluated in the Nd-Fe-B films with several coercivity by HRTEM. The lattice constant of fcc NdO_x and C-Nd_2O_3 phases have variation about 5~10%. On the contrary, lattice constant of hcp Nd_2O_3 phase have hardly variation. Microstructural observation shows that the interface of Nd_2Fe_(14)B/C-Nd_2O_3 (or fcc NdO_x) is flat, however there is some defects at the interface of Nd_2Fe_(14)B/hcp Nd_2O_3. The interface of Nd_2Fe_(14)B/hcp Nd_2O_3 exists dominantly in the Nd-Fe-B films with low coercivity. Therefore, the strain induced at the interface of Nd_2Fe_(14)B/hcp Nd_2O_3 is thought to be larger than Nd_2Fe_(14)B/C-Nd_2O_3 (or fcc NdO_x) and that leads to decrease the coercivity.