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)(12-2x)TixVx (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 (H-c) 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 H-c 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)10.8Ti(0.6)V(0.6) + y wt. % Cu-Ga (1 = y = 3), to enhance the H-c. 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 H-c 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.