High coercivity in mechanically milled ThMn12-type Nd–Fe–Mo nitrides

Starting from carefully homogenized Nd10Fe90-yMoy (y=12, 10, 7) alloys and by appropriate mechanical milling, the as-milled microstructure consisting of a nanoscale mixture of severely distorted 1:12 phase and substitutional α-Fe-based solid solution was obtained. This kind of as-milled microstructure was thought to have a critical effect on the formation of iron-free nanocrystalline 1:12 phase during subsequent annealing. Upon nitrogenation, the sample of Nd10Fe78Mo12Nx exhibited a record-high coercivity of 13.1 kOe at 293 K. Measurements of initial magnetization curve and a family of demagnetization curves engendered under different maximum applied fields Hm were carried out, and the results revealed the domain-wall pinning at grain boundaries as the coercivity mechanism. A low Mo-content sample of Nd10Fe83Mo7Nx with iHc∼5.8 kOe, Br∼6.8 kG, and (BH)max∼7.0 MG Oe was made by optimizing the preparation conditions.