Submicron R2Fe14B particles

Mechanochemical synthesis of submicron R2Fe14B particles with R = Dy, Nd, Pr has been performed successfully via high energy ball milling of rare-earth oxides, iron oxide and boron oxide in the presence of a reducing agent (Ca) and a dispersant material (CaO), followed by annealing at 800 - 900 degrees C. In the R = Nd system, we were able to fabricate particles embedded in a CaO matrix with coercivity (H-c) of 10.3 kOe after annealing at 900 degrees C for 5 min. After washing off the dispersant, the H-c was decreased to below 1 kOe because of hydrogen absorption that leads to the formation of the hydrated R2Fe14BHx phase that has a lower anisotropy. Upon removal of the hydrogen the coercivity was increased to 3.3 kOe. The average size of the Nd2Fe14B particles increases from 100 nm in a sample synthesized at 800 degrees C to 158 nm at 900 degrees C. The isotropic Dy2Fe14B particles showed a higher coercivity of 21 kOe in washed samples after annealing at 900 degrees C for 5 min. An average size of 71 nm is measured in samples synthesized at 800 degrees C and 107 nm at 900 degrees C. Fitting the high field M(H) measurements in Nd2Fe14B to the law of approach to saturation gave values for the magnetocrystalline anisotropy for the washed sample 2.23 x 10(7) erg/cm(3) and for the vacuum annealed sample 4.15 x 10(7) erg/cm(3), both of which are lower than the bulk values. This would explain the lower values of H-c observed in the particles. (C) 2016 Author(s).