The ThMn₁₂-type SmFe₁₂-based rare-earth permanent magnet has attracted widespread attention due to its excellent intrinsic magnetic properties and high-temperature stability. However, the challenge in realizing continuous non-magnetic or weakly magnetic grain boundary phases equilibrated with the SmFe₁₂ main phase hinders the enhancement in extrinsic magnetic properties of the SmFe₁₂-based permanent magnet, especially for the coercivity. In this work, by controlling the cooling rate, the uniform distribution of paramagnetic Fe₂Ti phases at grain boundaries is achieved in the SmFe₁₂-based alloy ribbon, resulting in a high coercivity of 7.95 kOe. This improvement is attributed to the elimination of the impurity phase within the SmFe₁₂ main phase and the magnetic isolation effect of the grain boundary phase composed of paramagnetic Fe₂Ti, which is directly observed by transmission electron microscopy and further confirmed by micromagnetic simulation. Moreover, first-principles calculations show that the V element can dope into Fe₂Ti and facilitate the transition of its paramagnetic state at room temperature. This study provides new insights into constructing weakly magnetic grain boundary phases for SmFe₁₂-based permanent magnets, offering a novel approach to enhance coercivity.

Due to the rare earth supply shortage, ThMn₁₂-type RFe₁₂-based (R is the rare earth element) magnets with lean rare earth content are gaining more concern. Most ThMn₁₂-type RFe₁₂ structures are thermodynamically metastable and require doping of the stabilizing element Ti. However, the Ti-doping effects on the hard magnetic properties of RFe₁₁Ti have not been thoroughly investigated. Herein, based on density functional theory calculations, we report the Ti-doping effects on the phase stability, intrinsic hard magnetic properties and electronic structures of RFe₁₁Ti (R = La, Ce, Pr, Nd, Sm, Y, Zr). Our results indicate that Ti-doping not only increases their phase stability, but also enhances the magnetic hardness of ground-state RFe₁₂ phases. Particularly, it leads to the transition of CeFe₁₁Ti and PrFe₁₁Ti from easy-plane to easy-axis anisotropy. Charge density distributions demonstrate that Ti-doping breaks the original symmetry of the R-site crystal field, which alters the magnetic anisotropy of RFe₁₁Ti. Projected densities of states reveal that the addition of Ti results in the shift of occupied and unoccupied f-electron energy levels of rare earth elements, affecting their magnetic exchange. This study provides an insight into regulating the hard magnetic properties of RFe₁₂-based magnets by Ti-doping.