Effects of Ti–V pair substitution and grain boundary modification on physical and magnetic properties of Sm(Fe0.8Co0.2)12 bulk magnet

We successfully fabricated high-density Sm(Fe0.8Co0.2)12–2xTixVx (0.6 ≤ x ≤ 1.0) bulk magnets with high-purity ThMn12-type phase through the bulking of amorphous powder and subsequent annealing process. Depending on the Ti–V pair concentrations, the physical and magnetic properties including lattice constants, crystallized phases, magnetizations (M), and coercivities (Hc) of the fabricated samples were investigated. The highest maximum energy product, (BH)max, of 7.293 MGOe was obtained with x = 0.6; however, its Hc was limited to 3379 Oe due to the absence of a grain boundary phase, despite the average grain size being within 81 nm, which is close to the single domain size. Thus, an intergranular phase was developed by introducing Cu–Ga additive, i.e., Sm(Fe0.8Co0.2)10.8Ti0.6V0.6 + y wt. % Cu–Ga (1 ≤ y ≤ 3), to enhance the Hc. Uniform grain boundaries with Sm-rich phases were crystallized for y ≥ 2, and their thicknesses increased with higher y; the thickness of the grain boundary for the sample with y = 2 was 12 nm. The Hc of the samples with uniform grain boundaries were significantly enhanced from 3379 Oe to 4054 and 4317 Oe for y = 0 and y = 2 and 3, respectively. This paper presents the results of Ti–V pair substitution and grain boundary modification in an effort to improve magnetic properties by controlling crystalline phases, grain sizes, and grain boundaries.