Realizing a non-ferromagnetic intergranular phase for the ThMn12-type Sm(Fe,Co,Ti)12 compound is a prerequisite for developing high coercive magnets. In this work, we demonstrate that the addition of Ga into the Sm-(Fe,Co)-Ti system results in the formation of non-ferromagnetic Sm–Ga-rich intergranular phases with good wettability on Sm(Fe,Co,Ti)12 grains. In the Sm-(Fe,Co)-Ti system, when the alloy composition was varied to the Sm-rich region as Sm1+w(Fe0.8Co0.2)11Ti (w = 0–0.7), soft ferromagnetic C15-type Sm(Fe,Co)2 intergranular phase and TbCu7-type Sm(Fe,Co,Ti)~7 phase formed along with the ThMn12-type main phase in the as-cast alloy. We demonstrated that by introducing Ga, the formation of these secondary soft ferromagnetic phases can be hindered as the excess Sm and Ga formed non-ferromagnetic Ba5Si3-type Sm5Ga3 and TII-type SmGa intergranular phases with an excellent wettability on Sm(Fe,Co,Ti)12 grains. Fine Sm(Fe,Co,Ti)12 grains of 1–2 µm, well isolated by the Sm–Ga-rich intergranular phase, were realized by melt-spinning the Ga-doped alloy and the maximum coercivity obtained was 0.5 T. According to the detailed microstructure characterizations, the weak-links to the coercivity of this novel microstructure of well-isolated and fine Sm(Fe,Co,Ti)12-based grains is the presence of defects at the interfaces which could lead to a locally reduced magneto-crystalline anisotropy.
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